Slutrapport/Final report VINNOVA SIO IoT – Dnr 2014-05164

DokID: Slutrapport SIO IoT Dnr2014-05164_Acreo_offentlig_160209.docx

Date/Datum

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Approved/Godkänd

Type of document/Dokumenttyp

REPORT

Issued by/Utfärdare

Peter Dyreklev

Reference/Referens

Distribution

VINNOVA

For information only/För kännedom

HiQ, LiU/LOE

Slutrapport/Final report VINNOVA SIO IoT – Dnr 2014-05164

Introduction

The present document is the final report from the VINNOVA SIO IoT project “energikällor för IoT” Dnr

2014-05164. The report is written in English, since the work has partly been done by non-swedish speak-

ing researchers.

The project was carried out during the period 141201-150930. The project partners are Acreo Swedish

ICT in Norrköping (Acreo), Laboratory of Organic Electronics, Linköping University in Norrköping

(LiU) and HiQ in Norrköping/Linköping.

Background

Internet (Internet of things/IoT) is already today a reality in which more objects get connected and begin

to communicate with the surrounding world. In many applications, the new IoT functionality must have a

sufficiently low cost to be realized and become attractive to the product owner and the end user. The low

manufacturing cost in large volumes can be accomplished by using new manufacturing methods that use

printed electronics combined with traditional silicon technology. Common to basically all applications is

the need for electrical energy to power the devices. The energy supply for the IoT object is today a large

challenge and is limiting the development and thus the use and spread of IoT. Batteries (primary or sec-

ondary) are often used, but the cost and environmental impact (need for recycling) calls for other alterna-

tives.

This project has had the aim to understand the requirements for energy sources for IoT-applications and

identify limitations in presently available solutions and suggest future needed research and development.

Outline

In the present work Acreo and LiU have reviewed available energy sources from a printed electronics

point-of-view. Together with an analysis of HiQ’s customers’ needs, a matching of energy sources and

system requirements has been done. The IoT applications has been chosen as three different cases repre-

sentative for more applications.

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Energy sources

This section of the report summarizes energy sources that possibly could be useful for IoT applications.

Besides energy sources, also supercapacitors are considered since energy harvesting often requires energy

storage.

Printed Batteries

There are different types of flexible batteries, with Li and rechargeable Li ion batteries as the commercial-

ly dominant ones. There are just a few commercially available printed batteries, and they mostly utilize

Zn as anode material. Prices for printed batteries are relatively high and processes are immature and their

performance are not ideal. The competition from technologies like flexible Li and Li ion batteries is

strong. Still, judging by the potential for further development and the advantage of safety and material

cost, it is optimistic to speculate that a breakthrough with printed Zn battery is desirable and viable.

Commercially available printed batteries

There are a few commercially available printed batteries. They are listed in Table 1.

Manufacturer Type Capacity (mAh)

Thickness (mm)

Size (mm)

Printing method

Enfucell Zn-MnO2 10-90 0.7 36x46; 60x72; 60x42 Screen print + lamination

Bluespark Zn-MnO2 5-37 0.5 26x63; … 79x47 Stencil?

Rocket Zn-MnO2 1.5-40 0.6-1.3 20mm; … 55x55 Lamination

Solicore Li-MnO2 10-25 0.45 25,75x29; 48,75x23 Screen print; digital printing

Table 1 Commercially available printed batteries

Comments and references to Table 1.

http://files.kotisivukone.com/enfucell.kotisivukone.com/kuvat/softbattery/enfucell_softbattery_specifications_nov2014_2.pdf

http://www.bluesparktechnologies.com/images/PDFs/Blue_Spark_UT_Series_Batteries_Jan_14_1.pdf

http://www.solicore.com/

http://www.rocket.co.kr/english/r_d/0battery.asp

http://www.rocketpoland.com/en/text/6,13-BATERIE_PAPIEROWE.php

http://www.rocketpoland.com/en/text/6,14-LITHIUM_FLEXIBLE_BATTERY.php

.

Competing commercial thin and flexible/bendable battery technologies

A general overview is available in e.g., “A review of the present situation and future developments of

micro-batteries for wireless autonomous sensor systems”: http://onlinelibrary.wiley.com/doi/10.1002/er.2949/abstract

Examples of commercially available batteries are compiled in the table below.

Manufacturer Battery type Performance References

GM Battery

Thin Lithium battery Nominal capacity：18mAh

Rated voltage：3.0V

Max. continuous current ：9mA

Max. peak current ：40mA

Mass ：0.5g

Thickness：0.45mm

http://www.gmbattery.com/

Cymbet

Powerstream

Rechargeable flexible thin

Lithium ion battery

2mAh/cm2

3,6V

3 USD/pc in large volumes

http://www.cymbet.com/products/enerchip-solid-state-batteries.php

http://www.powerstream.com/thin-

http://files.kotisivukone.com/enfucell.kotisivukone.com/kuvat/softbattery/enfucell_softbattery_specifications_nov2014_2.pdf

http://www.bluesparktechnologies.com/images/PDFs/Blue_Spark_UT_Series_Batteries_Jan_14_1.pdf

http://www.solicore.com/

http://www.rocket.co.kr/english/r_d/0battery.asp

http://www.rocketpoland.com/en/text/6,13-BATERIE_PAPIEROWE.php

http://www.rocketpoland.com/en/text/6,14-LITHIUM_FLEXIBLE_BATTERY.php

http://onlinelibrary.wiley.com/doi/10.1002/er.2949/abstract

http://www.gmbattery.com/



http://www.powerstream.com/thin-lithium-ion.htm

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lithium-ion.htm

Cymbet

Seiko Instruments Inc

Chip battery Typical capacity 10-50 uAh @

area 0,5 cm2. Voltage 3,8V. http://www.cymbet.com/products/enerchip-solid-state-batteries.php http://www.micross.com/pdf/Cymbet_EnerChip_CBC050.pdf

http://www.sii.co.jp/en/me/battery/support/selectguide/

Seiko Instruments Inc Coin batteries

Type MS412FE

Nominal Voltage (V) 3

Nominal Capacity(mAh) 1.0

Internal Impedance(Ω) 100

Standard Charge Discharge

Current(mA) 0.010

Maximum Discharge Current

(Continuous)(mA) 0.10

Size Diameter(mm) 4.8

Size Height(mm) 1.2


Research on flexible/thin/printed batteries:

Patent search on “Printed battery” gives more than 9000 hits in google patent search, and the oldest regis-

tered patents dates back to 1951. https://www.google.se/search?tbm=pts&hl=sv&q=printed+battery

Zn-MnO2 primary batteries

Fraunhofer ENAS

At Fraunhofer ENAS Baumann et al. has developed printed batteries.

The batteries are of the Zn-MnO2 type and has the following performance

http://www.enas.fraunhofer.de/content/dam/enas/de/documents/Downloads/datenblaetter/PrintedBatteries_EN_web.pdf

HDM and Varta collaboration

Varta and Hochschulen der Media has collaborated on printed battery development. Their work is e.g.

reported here https://www.hdm-stuttgart.de/international_circle/circular/issues/11_01/ICJ_04_32_wendler_huebner_krebs.pdf

As far as we know, no commercialisation has yet been done.

http://www.powerstream.com/thin-lithium-ion.htm



http://www.micross.com/pdf/Cymbet_EnerChip_CBC050.pdf

http://www.micross.com/pdf/Cymbet_EnerChip_CBC050.pdf





https://www.google.se/search?tbm=pts&hl=sv&q=printed+battery

http://www.enas.fraunhofer.de/content/dam/enas/de/documents/Downloads/datenblaetter/PrintedBatteries_EN_web.pdf

https://www.hdm-stuttgart.de/international_circle/circular/issues/11_01/ICJ_04_32_wendler_huebner_krebs.pdf

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Flexible Alkaline Batteries

Various approaches to alkaline batteries are found in research literature. Below follows a few examples.

With Multiwalled Carbon Nanotubes and Copolymer Separator:

http://onlinelibrary.wiley.com/doi/10.1002/adma.201304020/abstract

Highly Flexible, Printed Alkaline Batteries Based on Mesh-Embedded Electrodes


Intrinsically stretchable and rechargeable batteries for self-powered stretchable electronics

http://pubs.rsc.org/en/Content/ArticleLanding/2013/TA/c3ta00019b#!divAbstract

Highly Stretchable Alkaline Batteries Based on an Embedded Conductive Fabric


Air-stable, high energy density printed Zn-AgO2 battery

A printed high energy density silver oxide battery produced by stencil printing has been reported. A pho-

topolymerized polyacrylic acid separator layer enables a printed flexible battery capable of high rates of

discharge. The batteries show no difference in discharge upon flexing at a bend radius of 1.0 cm, indicat-

ing their potential in flexible applications. The fabricated batteries have demonstrated high energy densi-

ties of 10 mWh/cm3 and areal capacities of 5.4 mAh/cm2.

http://www.eecs.berkeley.edu/Pubs/TechRpts/2015/EECS-2015-33.html

Biological energy sources

Brief description

Biological power sources that provide electrical energy come in a few different forms. We have found the

following:

Bio-batteries (enzyme batteries), where enzymes break down glucose to release electrons.

If fuel can be refilled, we instead have enzymatic biofuel cells.

Microbial fuel cells (MFCs), where electricity is produced from organic materials using

living bacteria as the electrode catalyst

Soil current (soil bacteria producing current from sugar, which in turn is produced by

plants, e.g. grass)

Bio-batteries

Enzyme batteries and enzymatic biofuel cells work according to the same principle as shown in Figure 1

below. Enzymes are used as catalysts to produce electrons and protons from sugar (typically glucose), and



http://pubs.rsc.org/en/Content/ArticleLanding/2013/TA/c3ta00019b#!divAbstract


http://www.eecs.berkeley.edu/Pubs/TechRpts/2015/EECS-2015-33.html

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the charges are harvested at electrodes to produce an electric current. More information at

http://en.wikipedia.org/wiki/Enzymatic_biofuel_cell. If glucose can be added, we have a fuel cell. If the

system is closed, including a fixed amount of glucose, we call it an enzyme battery.

Figure 1 Enzymatic biofuel cell

Sony published a press release in 2007: http://www.sony.net/SonyInfo/News/Press/200708/07-

074E/index.html#r=s where they show a “bio-battery” that runs on glucose and delivers 50 mW.

VTT claims to have tested a printable bio-battery: http://www.vttresearch.com/services/digital-

society/wearable-technology/autonomy-of-energy/printed-and-custom-shape-power-sources .

The battery is activated by moisture. It is unclear whether this bat-

tery is fully printed or if only the printing of the different layers has

been demonstrated.

Microbial Fuel Cells

Basic definition can be found at

http://en.wikipedia.org/wiki/Microbial_fuel_cell

The concept is similar to enzyme batteries/fuel cells, but in MFCs the conversion of fuel occurs in living

cells (typically bacteria) instead of enzymes.

General BES (bioelectrochemical system) concept (from [4]) is shown below.

http://en.wikipedia.org/wiki/Enzymatic_biofuel_cell

http://www.sony.net/SonyInfo/News/Press/200708/07-074E/index.html#r=s

http://www.sony.net/SonyInfo/News/Press/200708/07-074E/index.html#r=s

http://www.vttresearch.com/services/digital-society/wearable-technology/autonomy-of-energy/printed-and-custom-shape-power-sources

http://www.vttresearch.com/services/digital-society/wearable-technology/autonomy-of-energy/printed-and-custom-shape-power-sources

http://en.wikipedia.org/wiki/Microbial_fuel_cell

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Soil current

Soil current is a special case of MFCs, where the fuel is provided by a plant growing on top of the fuel

cell and the bacteria and electrodes are placed in the soil below the plant.

Power/Energy output

Sony has reported 50 mW power output from a bio-battery, approximately cube-shaped with 39 mm

sides. This corresponds to 0,84 kW/m3.

In ref [5], an enzymatic fuel cell is reported that produces 1,1 µW in a space of 0,01 mm3. This corre-

sponds to 110 kW/m3.

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VTT does not give any figures for the printed bio-battery [6] but a short video clip indicates that a voltage

of 1.3 V is obtained [7].

Sediment-based MFCs: Example in [3] gives 312 mW/m2 (in a 10 cm thick device) at 0.32 V. In constant

operation (days), around 225 mW/m2 (in a 10 cm thick device) at 0.30 V. Values up to 800 mW/m2 have

been reported by other groups.

Soil power: 500 mW/m2 (2012), aim 1,6 W/m2 [2]

Generally, bioelectrochemical systems (BESs) are claimed to be able to supply around 0.1 kW/m3 [4] as

compared to, e.g., conventional Li-ion batteries with 90 kW/m3.

Ref [4] is useful with several tables summarizing state-of-the-art.

Energy input

Soil power: Solar energy – sugar – bacteria – electrons – current. “Plant generators continue to work after

dark.”

Enzyme batteries: Run on glucose, that needs to be supplied.

Both enzyme and microbial fuel cells need the enzymes/microbes to work efficiently, which places limi-

tations on the operating conditions. Enzymes are more stable than microbes, with operating conditions

typically between 20-50 °C and pH 4.0 to 8.0.

Form factor

MFCs: Rather bulky because of the thickness.

Enzyme batteries: Can be printed according to VTT [6] and made very small [5].

According to the video material available from VTT, the printed enzyme batteries seem to be around 4x6

cm in size for the full battery, with electrodes being around 4x4 cm. Including substrates, the fully assem-

bled battery is probably 1-2 mm thick.

Cost

No cost analysis available. The only printed solution in this report, the VTT enzyme battery, involves

standard printing methods but the materials are undisclosed and therefore costs cannot be estimated. VTT

states that “production costs should be reasonable” [6].

Production

Carbon/graphite electrodes are used in some MFC applications and should be printable.

Enzyme batteries can be fully printed according to VTT, who claim to have demonstrated “R2R pro-

cessability (including drying) of the biologically active materials and the manufacturing of anodic and

cathodic layers by means of rotary screen printing”. Humidity/water is needed for operation, though, and

has to be added at the time when the battery is required to start producing power.

No special enclosures or heating/cooling equipment is visible in the VTT videos of enzyme battery print-

ing, so we conclude that these materials can be printed at room temperature and atmosphere.

Environment

Generally good for the environment; MFC will even reduce CO2 emission. Bio-batteries should be possi-

ble to recycle entirely.

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Technology readiness, R&D needs

MFCs have been known for a long time and are commercially used since ~2000 in wastewater treatment.

Bio-batteries are heavily researched, and even the US army has shown interest, but no commercial prod-

ucts are sold as far as we can find.

The major benefit of enzyme batteries in printed electronics applications is probably the possibility to

produce an entirely bio-degradable power source, where the fuel source is renewable.

Major limitations for use in printed electronics applications include bulkiness (MFCs in general), limited

printability (MFCs) and the need to activate the power source with moisture (enzyme batteries). However,

in some applications it may be easy to provide this moisture, or even desirable to have a power source

that starts working when moisture is applied. Applied research should focus on these types of applica-

tions. For MFCs, more fundamental research into materials and mechanisms is needed before competitive

alternatives on small-size scales can be launched [4].

References

[1] Soil current: http://www.plantpower.eu/

[2] Soil current: Popular science article in New Scientist, Feb 11, 2012, page 46

[3] A single sediment-microbial fuel cell powering a wireless telecommunication system:

http://www.sciencedirect.com/science/article/pii/S0378775313007933#

[4] 100 years of microbial electricity production: three concepts for the future

http://onlinelibrary.wiley.com/doi/10.1111/j.1751-

7915.2011.00302.x/abstract;jsessionid=6C947C0CDF29D004DD2C881D78393C64.f01t03

[5] Michael J. Moehlenbrock; Shelley D. Minteer: Extended lifetime biofuel cells. Chemical Society Re-

views , May2008, Vol. 37 Issue 6, p1188-1196

[6] VTT printed bio-battery:

http://www.vtt.fi/files/services/ele/Biobatteries_convert_sugar_to_electricity.pdf

[7] VTT printed bio-battery, video of battery voltage(?) measured by DVM:

https://www.youtube.com/watch?v=pIpHpn4RCLE

Photovoltaics

Introduction

There are many possibilities for converting solar energy into electrical power for IoT applications. How-

ever, the physical reality is a difficult choice in terms of cost, size, form factor, reliability and energy-

transfer efficiency. The light-to-electricity conversion efficiency () for most popular solutions is summa-

rized in Figure 2.

http://www.plantpower.eu/

http://www.sciencedirect.com/science/article/pii/S0378775313007933

http://onlinelibrary.wiley.com/doi/10.1111/j.1751-7915.2011.00302.x/abstract;jsessionid=6C947C0CDF29D004DD2C881D78393C64.f01t03

http://onlinelibrary.wiley.com/doi/10.1111/j.1751-7915.2011.00302.x/abstract;jsessionid=6C947C0CDF29D004DD2C881D78393C64.f01t03

http://www.vtt.fi/files/services/ele/Biobatteries_convert_sugar_to_electricity.pdf

https://www.youtube.com/watch?v=pIpHpn4RCLE

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Figure 2 Best research-cell efficiencies by NREL (for 1 sun, AM1.5, solar cell with 1m² surface area producing 100 watts

of power is measured at 10% power conversion efficiency ()

Following requirements for solar energy sources were taken under account when preparing this summary:

1. Availability of commercial solutions

2. Impact of low light and angle of incident light on solar cell performance (in-door applications)

3. Diversity of sizes (low thickness)

4. Device flexibility/bendability

5. Simplicity of technological implementation

6. Integration ability with printed electronics

Multijunction solar cells

Brief description

Multijunction solar cells feature layers, each tuned to different wavelength bands in the solar spectrum. It

is like few different solar cells stacked together. The main manufacturer is MicroLink Devices

(www.mldevices.com, USA). Photographs and simplified structures of these devices are presented in

Figure 3. However, typical multijunction solar cell contains 10 - 20 layers (Poortmans & Arkhipov,

2006)(Tanabe, 2009).

http://www.mldevices.com/

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a)

b)

c)

d)

Figure 3 Photograph and structure of MicroLink’s: a) dual-junction cell, b) triple-junction cell, c) solar sheet (single, dual

or triple) and d) concentrator photovoltaics

Power/Energy output

The performance of MikroLink’s multijunction is summarized in

Table 2.

Parameter dual- junction triple-junction

= 26.2 % 30 %

P = 200 W/m2 250 W/m2

areal mass density = 250 g/m2 250 g/m2

specific power = 800 W/kg 1000 W/kg

JSC = 13.43 mA/cm2 12.7 mA/cm2

VOC = 2.34 V 2.83 V

Table 2 MikroLink solar cell performance

Energy input

The spectrum of light is effectively divided into bands and absorbed by constituted junction. Therefore

the device captures blue, visible and infrared light. More specifically, dual-junction cell harvests light in

the range of 350 - 900 nm, while triple-junction cell harvests light in the range of 350 - 1250 nm

Form factor

Microlink cell are produced in following dimensions: 66 x 31 mm, 20 x 20 mm, 10 x 10 mm. Other di-

mensions are available on request. These cells are thin, less than 40 µm, and flexible to use on curved

surfaces.

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Cost

Costs are reduced because GaAs substrate can be reused for subsequent growths of additional solar cells.

However, these PV devices are still the most expensive on the market and used mainly in military, satel-

lites and drones.

Production

MicroLink grows cells using metal organic chemical vapor deposition (MOCVD). These devices are

manufactured using epitaxial lift-off technology, in which the solar cell is removed from the substrate on

which it is grown. It is not compatible with printed techniques.

Environment

PV manufacturers using MOCVD currently employ sophisticated engineered systems to isolate hazardous

materials from the workplace and to monitor for potential employee exposures.


The technology is already establish. Multi junction cell can be fabricated either by mechanical stacking of

various layers or each semiconductor layer can be monolithically grown on top of the other molecular

organic chemical vapor deposition (MOCVD).

References

Poortmans, J., & Arkhipov, V. (2006). Thin film solar cells: fabrication, characterization and

applications. Solar Cells. John Wiley & Sons

Tanabe, K. (2009). A review of ultrahigh efficiency III-V semiconductor compound solar cells:

Multijunction tandem, lower dimensional, photonic up/down conversion and plasmonic

nanometallic structures. Energies, 2, 504–530. doi:10.3390/en20300504

Single-junction GaAs based solar cell

Brief description

Gallium Arsenide (GaAs) is the highest performance solar technology currently available, boasting con-

version efficiencies in excess of 40% (at lab scale), nearly double those of crystalline silicon. The main

manufactures of these devices (see Figure 4) are Alta Devices (www.altadevices.com, USA), MicroLink

Devices (www.mldevices.com, USA) and NanoFlex (www.nanoflexpower.com, USA).

a)

b)

http://www.altadevices.com/

http://www.mldevices.com/

http://www.nanoflexpower.com/

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Figure 4 Gallium arsenide flexible solar cell from a) Alta Devices and b) MicroLink

Power/Energy output

The performance of GaAs solar cells manufactured by Alta Devices and MikroLink are summarized in

Table 3. It is worth to mention that GaAs PV cell from Alta Devices holds a world-record cell and mod-

ule efficiencies.

Parameter Alta Devices MikroLink

= 25% 21 %

P = 150 W/m2

Pmax = 214 mW

areal mass density = 250 g/m2

specific power = 600 W/kg

JSC = 233 mA/cm2 27.41 mA/cm2

VOC = 1.09 mV 0.99 V

Vmax = 0.9 V

Imax = 223 mA/cm2

FF = 0.84

Table 3 Alta Devices and MikroLink solar cells performance

Energy input

Single-junction GaAs cell harvests light in the range of 350 - 900 nm.

Form factor

The gallium arsenide based cells are thin, flexible and lightweight, enabling a broad range of mobile

power applications. Standard Alta Devices cell dimensions are presented in Figure 5. Standard MicroLink

cell dimensions are 66 x 31 mm, but other dimensions are available on request. MicroLink cell is thin,

less than 40 µm, and flexible to use on curved surfaces.

Figure 5 Sample products dimensions of flexible GaAs PV cells from Alta Devices

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Cost

High fabrication costs have made GaAs-based solar cells prohibitively expensive for mass markets and

have limited their application to space-borne and military sectors. Current price of Alta Devices solar

cells is $100/W because they are in low rate production. They plan to enter full-rate production in Q4

2015 - Q1 2016 and expect the price to fall. By the end of 2016, they expect the price to be around

$30/W. By the end of 2017, expect around $10/W.

Production

GaAs cells are manufactured using metal organic chemical vapor deposition (MOCVD) using epitaxial

lift-off technology, in which the solar cell is removed from the substrate on which it is grown.

Environment

GaAs PV manufacturers currently employ sophisticated engineered systems to isolate hazardous materials

from the workplace and to monitor for potential employee exposures.


The technology is already establish. A basic technique for GaAs single-junction cell is MOCVD.

References


Multijunction tandem, lower dimensional, photonic up/down conversion and plasmonic nanometallic

structures. Energies, 2, 504–530. doi:10.3390/en20300504

Nanostructured silicon solar cells

Brief description

It this approach Si NPs are manufactured on a rigid silicon, combined in cells and released from the sub-

strate creating ultrathin nanostructured microcells, as it is presented in Figure 6.

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Figure 6 Schematic illustration of fabrication steps of ultrathin ( 8µm), nanostructured silicon microcells (Lee et al.,

2014)

Power/Energy output

= 12.4% (for large scale)

ISC = 40.1 mA/cm2

VOC = 473 mV

Energy input

Cells exhibit good performance for incident angle of solar irradiation normal to the surface as well as for

angular dependence (bending).

Form factor

Very thin microcells (8µm). Lightweight and flexible construction.

Cost

Potentially low cost due to the reduced consumption of active materials and low requirements for materi-

als purity. However as PVD, CVD and lithographic techniques are involved, the throughput is low.

Production

Ultrathin silicon solar microcells integrated with engineered photonic nanostructures are fabricated direct-

ly from wafer-based source material via PVD, CVD and photolithography. Released microcells are then

integrated with any substrate patterned with electrodes for current collection (preferably metal for low

transfer resistance).

Environment

PV manufacturers using PVD and CVD techniques employ sophisticated engineered systems to isolate

hazardous materials from the workplace and to monitor for potential employee exposures.

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Concept developed so far only at a lab-scale.

References

Lee, S., Biswas, R., Li, W., Kang, D., Chan, L., Yoon, J., & Al, L. E. E. E. T. (2014). Printable

Nanostructured Silicon Solar Cells for High-Performance , Large-Area Flexible Photovoltaics. ACS

Nano, 8(10), 10507–10516. doi:10.1021/nn503884z

Lee, C. H., Kim, D. R., Zheng, X., Engineering, M., States, U., Engineering, M., & Science, N. (2014).

Transfer Printing Methods for Flexible Thin Film Solar Cells : Basic Concepts and Working Principles,

(9), 8746–8756.

Non-silicon thin film inorganic solar cells

Brief description

In CIGS PV cell which is known as the most successful case among all non-silicon thin film inorganic

cells the light passes through the ZnO layer, it is absorbed by the CIGS, creating electron-hole pairs. An

electric field created at the CIGS/CdS junction draws negatively charged electrons to the ZnO layer,

which generates a flow of positive charges in the opposite direction, producing an electric current. This

concept has been commercialized in a flexible form (see Figure 7) among others by Global Solar

(www.globalsolar.com, USA), International Solar Electric Technology (ISET, www.isetinc.com) which

produces printable cells and Solarion (www.solarion.net, Germany) in uses R2R processing.

a)

b)

c)

Figure 7 Flexible CIGS PV cell manufactured by a) Global Solar, b) ISET and c) Solarion

One of the potential suppliers for non-silicon thin film inorganic solar cells is www.natcoresolar.com

Power/Energy output

The performance of CIGS solar cells manufactured by Global Solar and ISET are summarized in Table 4.

Parameter Global Solar PowerFLEX ISET Solarion

= 12.6 % 14 %

P = 300 W/m2

http://www.globalsolar.com/

http://www.isetinc.com/

http://www.solarion.net/

http://www.natcoresolar.com/

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specific power = 1500 W/kg

PMAX = 8.3 W

JMAX = 475 mA

VMAX = 17.4 V

Table 4 Example of CIGS solar cells performances

Energy input

CIGS cell harvests light in the range of 375 - 1250 nm.

Form factor

A CIGS absorber film requires only 1-2µm of material to convert sunlight into electricity. Global Solar

PowerFLEX module has a format of 5.75 x 0.5 m. The smallest CIGS PV module from ISET in 305 x

305 mm.

Cost

Potentially low material costs. Nanosolar claimed that the costs of making electricity from sunlight is

around 30 cents per watt. However, the company bankrupted in 2013.

Production

CIGS PV cells are manufactured by depositing a thin layer of copper, indium, gallium and selenide on

glass or plastic backing, along with electrodes on the front and back to collect current. CVD has been

implemented in multiple ways for the deposition of CIGS and it is current main deposition technique.

Other techniques applied in CIGS PV manufacturing are sputtering, and co-evaporation.

A non-vacuum-based alternative process deposits nanoparticles of the precursor materials on the substrate

via printing techniques, electrodeposition or electrospray.

Environment

H2Se used in CVD is highly toxic and is classified as an environmental hazard.

ISET claims that films deposited using non-vacuum-based process are processed in an open-air environ-

ment as the printed materials do not exhibit toxicity.


Production of CIGS solar cells via CVD is well established. However, printing methods are still under

development and the solution provided by ISET is not widely available. It seems that ISET unsuccessful-

ly attempted to scale up printing process and their modules are still co-evaporated.

Perovskite thin film solar cells

Brief description

This type of solar cell includes a perovskite absorber, most commonly a hybrid organic-inorganic lead or

tin halide-based material, as the light-harvesting active layer as presented in Figure 8. This concept is

being commercialized by Oxford PV (www.oxfordpv.com, UK) which is planning to produce attractively

http://www.oxfordpv.com/

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colored and semi-transparent glass, which works as a solar cell and could be integrated into the facades of

buildings and windows.

a)

b)

Figure 8 Schematic structure of perovskite-based a) hybrid solar cell structure (Conings et al., 2014) and b) Mesosu-

perstructured Solar Cells (MSSCs) developed by Oxford PV

Power/Energy output

The performance of perovskite-based hybrid devices is the following (Conings et al., 2014):

= 10.8 %

ISC = 21.3 mA/cm2

VOC = 0.932 mV

FF = 0.544

Prototypes of printed Meso-Superstructured Solar Cells (MSSC) developed by Oxford PV have achieved

a conversion efficiency record for the technology of 17% (February 2014).

The performance of perovskite solar cell developed by VTT is roughly five times better than that of a

typical organic photovoltaic cell, but no specific value is provided.

Energy input

Perovskite-based hybrid device harvest sun energy in a range of 300 – 800 nm.

Form factor

The active film of perovskite cell has typically a thickness of 100-300 nm.

Cost

Perovskite absorber materials such as methylammonium or formamidinium lead halide are extremely

cheap to produce and simple to manufacture. According to VTT experience, material costs can be ten

times lower than in case of organic solar cells.

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Production

Can be printed or spin-coated directly onto glass with the assistance of vapor deposition techniques to

produce a transparent, colored coating. Both processes hold promise in terms of scalability. However, the

predictions says that first commercial perovskite solar cell will be available in 2017.

Environment

Due to the instability of CH3NH3SnX3 when exposed to oxygen and moisture, all material and device

processing has to be conducted in a nitrogen-filled glovebox. However, resent report shows a lead-free

and non-toxic alternative to current perovskite solar cell technology (Noel et al., 2014).


VTT is currently examining how well the roll-to-roll printing methods are suited to the manufacturing of

inorganic solar panels made from perovskite materials. The first perovskite solar cells manufactured in

the laboratory using solution-based processes have been promising. VTT is also developing a method to

utilize light in wireless data transfer by using solar cells as data receivers. This will open new application

possibilities to utilize printable solar cells e.g. in IoT type applications.

References

Conings, B., Baeten, L., De Dobbelaere, C., D’Haen, J., Manca, J., & Boyen, H. G. (2014). Perovskite-

based hybrid solar cells exceeding 10% efficiency with high reproducibility using a thin film

sandwich approach. Advanced Materials, 26, 2041–2046. doi:10.1002/adma.201304803

Wang, J. T. W., Ball, J. M., Barea, E. M., Abate, A., Alexander-Webber, J. a., Huang, J., … Nicholas, R.

J. (2014). Low-temperature processed electron collection layers of graphene/TiO 2 nanocomposites

in thin film perovskite solar cells. Nano Letters, 14, 724–730. doi:10.1021/nl403997a

Noel, N. K., Stranks, S. D., Abate, A., Wehrenfennig, C., Guarnera, S., Haghighirad, A.-A., … Snaith, H.

J. (2014). Lead-Free Organic-Inorganic Tin Halide Perovskites for Photovoltaic Applications.

Energy & Environmental Science, 7, 3061–3068. doi:10.1039/C4EE01076K

Flexible silicon solar cells

Brief description

Rapid prototyping of IoT systems can be powered via hybridization with flexible PV cell (see Figure 9)

manufactured for example by PowerFilm Solar (www.powerfilmsolar.com, USA). The broader source of

such devices is www.flexsolarcells.com . It offers OEM components, rollable and foldable panels.

Figure 9 OEM a-Si PV components manufactured by PowerFilm Solar and distributed via www.flexsolarcells.com

Another potential supplier of flexible a-Si solar cells is Natcore Technology (www.natcoresolar.com,

USA). Crystalline silicon (c-Si) and polycrystalline (poly-Si) solar cells are also commercially available

from Solbian (www.solbian.eu, Italy).

http://www.powerfilmsolar.com/

http://www.flexsolarcells.com/

http://www.natcoresolar.com/

http://www.solbian.eu/

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Power/Energy output

An example a-Si PV device from PowerFilm Solar: SP3-12 Flexible Solar Panel (the smallest offered

device) has the following nominal performance:

P = 0.0255 W

U = 3.0 V

I = 8.5 mA

ISC = 10.7 mA

VOC = 4.5 V

Flexible a-Si cells are reaching = 6.5% while c-Si PV solar cells from www.solbian.eu are reaching =

22.5%. poly-Si have slightly lower performance.

Energy input

a-Si has a higher bandgap (1.7 eV) than c-Si (1.1 eV), which means it absorbs the visible part of the solar

spectrum more strongly than the higher energy infrared portion of the spectrum.

Form factor

An example device from PowerFilm Solar presented in Figure 10, model: SP3-12 Flexible Solar Panel

(the smallest offered device) has the following dimensions:

Thickness = 0.2 mm

Size = 12.7 x 64 mm

Aperture size = 12.7 x 50.8 mm

Weight = 0.24 g

Figure 10 The smallest OEM PV cell manufactured by PowerFilm Solar model: SP3-12

Cost

Prices for the smallest PowerFilm Solar OEM PV cell provided by www.flexsolarcells.com are summa-

rized in Table 5.

Table 5 Prices of example OEM PV cell

http://www.solbian.eu/

http://www.flexsolarcells.com/

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Production

The production of Si thin films is based on the deposition a very thin layer of silicon by plasma-enhanced

chemical vapor deposition (PECVD) using silane and hydrogen gas. In case of flexible cells such as the

ones from PowerFilm Solar, each cell is created by depositing Si on a thin plastic substrate and then en-

capsulating the cells in either a Polyester coating or heavy duty Tefzel, a DuPont product.

Environment

Thin film Si PV manufacturers using PECVD currently employ sophisticated engineered systems to iso-

late hazardous materials from the workplace and to monitor for potential employee exposures.


The technology of producing thin film Si solar cells is well establish. These PV cells are commercially

significant in utility-scale photovoltaic power stations, building integrated photovoltaics or in small stand-

alone devices.

References

Konagai, M. (2011). Present status and future prospects of silicon thin-film solar cells. Japanese Journal

of Applied Physics, 50. doi:10.1143/JJAP.50.030001

Dye-sensitized solar cells (DSSCs)

Brief description

DSSC uses interpenetrating network of nanoscale metal oxide covered with monolayer of sensitizing dye

molecules. This type of PV is being scaled-up by G24 Power (www.gcell.com, UK), Sony

(www.sony.net, Japan), Oxford PV (www.oxfordpv.com, UK) and EXEGER (www.exeger.com, Swe-

den). So far only G24 Power is able to provide fully functional products (see Figure 11).

Figure 11 GCell Sample DSSC module from G24 Power

Power/Energy output

A confirmed record of = 14.1% of was achieved by Professor Michael Graetzel and his team at École

Polytechnique Fédérale de Lausanne (EPFL) at lab-scale. Some of the first pre-industrial prototypes have

the following performance:

http://www.gcell.com/

http://www.sony.net/

http://www.oxfordpv.com/

http://www.exeger.com/

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= 7.17% (NREL certified)

ISC = 14.49 mA/cm2

VOC = 0.7 V

FF = 0.70

Commercially available GCell Sample DSSC module has the following nominal performance at 1000

W/m2 solar irradiation:

Pmax = 0.5 W

Imin = 100 mA

U = 5.5 V

active aperture size = 200 x 150 mm

Sony Corporation also claims that has developed DSSC with =10% and is preparing for commercializa-

tion.

Energy input

DSSC operates in visible range of sun spectra. The main limitation of these devices comes from poor

optical absorption characteristics in near infrared region.

Form factor

DSSCs at lab scale are typically developed on a two 1-3 mm thick glass substrates. The thickness of opti-

cally active dye-synthesized semiconductor usually does not exceed 10 µm, while the thickness of elec-

trolyte is of several micro meters. Commercial products of G24 Power has a thickness of few millimeters.

Cost

Commercially available GCell Sample DSSC module cost 50 £ inc. VAT

Production

Printing techniques are applied in manufacturing of DSSCs at industrial scale. However, fully printed

DSSC processed at low temperature is still out of reach.

Environment

DSSCs can be produced with no toxic emissions as freely obtainable components. They are largely recy-

clable and environmentally friendly to run.


DSSCs are so far only capable of 12.3% efficiency at lab scale. If DSCs can be pushed up to 15% effi-

ciency, then they should become a cost-effective alternative.

References

Mehmood, U., Rahman, S., Harrabi, K., Hussein, I. a., & Reddy, B. V. S. (2014). Recent Advances in

Dye Sensitized Solar Cells. Advances in Materials Science and Engineering, 2014, 1–12.

doi:10.1155/2014/974782

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Polymer solar cells

Brief description

The material used to absorb the solar light in polymer solar cells, is an organic material such as a conju-

gated polymer. The most efficient solution up to date is presented in Figure 12. There are few companies

and research centers developing scalable production technology for printed plastic solar modulus: Eight19

(www.eight19.com, UK), mekoprint (www.mekoprint.dk, Denmark), Riso DTU National Laboratory for

Sustainable Energy (www.energy.dtu.dk, Denmark).

a)

b)

Figure 12 Schematic illustration of the example polymer solar cells: a) currently leading configuration of materials in

terms of efficiency (You et al., 2013), b) structure used in large area organic PV (Kang, Hong, Back, & Lee, 2014).

http://www.eight19.com/

http://www.mekoprint.dk/

http://www.energy.dtu.dk/

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The best performing industrially produced printed organic cell was announced in 2013 by Victorian Or-

ganic Solar Cell Consortium together with CSIRO (www.csiro.au, Australia), The University of Mel-

bourne and Monash University. A screen-printed singe PV panel has a nominal power of 10-50 W/m2 and

size of A3 format (see Figure 13).

a)

b)

c)

Figure 13 Printed organic PV panel from a) CSIRO’s, b) Riso DTU National Laboratory for Sustainable Energy (Ander-

sen et al., 2014) and c) VTT

Frederik Krebs and his research team at the Technical University of Denmark have also demonstrated the

successful roll-to-roll manufacture of tandem OPV modules, each comprised of a stack of 14 discrete

layers, which are rapidly printed, coated or deposited one on top of another by a machine reminiscent of a

printing press

Power/Energy output

The performance of polymer solar cell is summarized in Table 6 and Table 7.

Low area (≤20 mm2) tandem cell Single-layer devices High area

= 10.6% (You et al., 2013)

ISC = 10.1 mA/cm2

VOC = 1.53 mV

FF = 0.68

= 6.5% (Dou et al., 2012)

ISC = 13.5 mA/cm2

VOC = 0.74 mV

FF = 0.65

= 6.2% (Kang et al., 2014)

ISC = 4.82 mA/cm2

VOC = 0.68 mV (one cell)

FF = 0.63

Table 6 Performance of lab-scale organic solar cells

Printed panel: VOSCC-CSIRO R2R Printed panel: Riso DTU R2R Printed decorative panel: VTT

W = 10-50 W/m2

Size = A3

= 1.76%

active surface area = 52.2 m2

W = 10.4 W (200 panels, 1m2)

I = 3.2 A

Table 7 Performance of organic solar cells developed at pre-industrial scale

http://www.csiro.au/

http://www.dtu.dk/english/Service/Phonebook/Person?id=3454&tab=2&qt=dtupublicationquery

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Energy input

Organic solar cells operates in visible spectrum of 350-650 nm. In order to broader the harvested range of

solar radiation a tandem structure can be used (up to 900 nm). Moreover, tandem structure minimize a

thermalization loss of photon energy (You et al., 2013).

Form factor

Typically 100-300 nm thick devices.

Cost

Polymer solar cells are an attractive approach to fabricate and deploy roll-to-roll processed solar cells that

are reasonably efficient (total PV system efficiency>10%), scalable and inexpensive to make and install

(<100 $/m2). At a cost of less than 1$/Wp, PV systems are potentially able to generate electricity in most

geographical locations at costs competitive to coal's electricity (at 5-6 cents/KWh).

Production

The main advantage of polymer solar cells is their ability to be produced from solution. So far a fully

printed cells is out of reach due to the necessity of ITO electrodes. The quality (conductivity) of that film

is critical for cell performance as it may impose significant ohmic loss. However in 2014 (+3 years) a big

project has been lunched between MERC and German Federal Ministry of Education and Research aim-

ing at fully printable organic (ITO-free) solar cell. The project is managed by KIT, Alexander Collsman.

Other materials for organic PV cells can be deposited using gravure-printing, screen-printing, slot-die and

spray in R2R processing (Krebs, 2009b)(Krebs, 2009a)(Andersen et al., 2014). However, the highest effi-

ciencies has been obtained via spin-coating. In order to limit aperture loss in large area devices a metal-

filament nanoelectrodes (vertically formed) can be applied (Kang et al., 2014).

Environment

An important aspect of large-scale fabrication of organic solar cells is the replacement of the commonly

used hazardous solvents. These solvents work well on lab-scale to investigate the fundamental working

principles of organic solar cells. However, on large-scale, eco-friendly materials are mandatory as the use

of toxic solvents would blow any budget due to expensive safety precautions.


Organic PV cells have finally reached efficiencies of about 10% at lab scale, which has been considered

as a barrier to the commercialization of this class of photovoltaics. It is expected that in the near future it

will reach 15% as there is a strong research activity on new donor and acceptor materials.

References

Andersen, T. R., Dam, H. F., Hösel, M., Helgesen, M., Carle, J. E., Larsen-Olsen, T. T., … Krebs, F. C.

(2014). Scalable, ambient atmosphere roll-to-roll manufacture of encapsulated large area, flexible

organic tandem solar cell modules. Energy & Environmental Science, 7(9), 2925–2933.

doi:10.1039/C4EE01223B

Dou, L., You, J., Yang, J., Chen, C.-C., He, Y., Murase, S., … Yang, Y. (2012). Tandem polymer solar

cells featuring a spectrally matched low-bandgap polymer. Nature Photonics, 6(February), 180–185.

doi:10.1038/nphoton.2011.356

Kang, H., Hong, S., Back, H., & Lee, K. (2014). A new architecture for printable photovoltaics

overcoming conventional module limits. Advanced Materials, 26, 1602–1606.

doi:10.1002/adma.201304235

Krebs, F. C. (2009a). Fabrication and processing of polymer solar cells: A review of printing and coating

techniques. Solar Energy Materials and Solar Cells, 93, 394–412. doi:10.1016/j.solmat.2008.10.004

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Krebs, F. C. (2009b). Polymer solar cell modules prepared using roll-to-roll methods: Knife-over-edge

coating, slot-die coating and screen printing. Solar Energy Materials and Solar Cells, 93(4), 465–

475. doi:10.1016/j.solmat.2008.12.012 You, J., Dou, L., Yoshimura, K., Kato, T., Ohya, K., Moriarty, T., … Yang, Y. (2013). A polymer tandem

solar cell with 10.6% power conversion efficiency. Nature Communications, 4, 1446.

doi:10.1038/ncomms2411

In-house solution

Outcome of the Tail of the Sun in which we are aiming at polymer-sensitized solar cell which is:

printed,

processed at low temperature (compatible with heat sensitive substrates),

all-solid-state,

optically active at IR spectra of the sun ,

stand-alone or coupled with dye-sensitized solar cell in a tandem

If we are able to reach all these requirements, we will have a perfect power source for IoT applications.

Project has started in January 2015 and will be executed for next 5 years. Preliminary results are going to

be presented within couple of months.

Resume

A photovoltaic cell converts the energy of light directly into electricity by the photovoltaic effect. The

range of absorbed wavelengths depends on the absorber on which a particular cell is based (see Figure

14).

Figure 14 The absorption spectra for various selected solar cells

Photovoltaic devices are available in large variety of sizes ranging from several mm2 (so-called micro-

cells) up to several m2 (PV panels). In terms of thickness the lower dimensions are achieved for devices

manufactured via thin film technology including: multijunction, nanostructured Si, non-Si thin inorganic

film, perovskite, a-Si, and polymer solar cells. Cells manufactured on Si wafer and DSSCs based on glass

are rather thick devices.

Cost of solar cells strongly depends on applied technology and materials. The potential/real cost hierarchy

is presented in Figure 15.

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Figure 15 Costs hierarchy for various selected solar cells

It seems to be essential for IoT application that the source of energy has ability to be manufactured solely

via solution processing, preferably printing. However, so far that goal has not been achieved. An over-

view of technologies applied in manufacturing of selected solar cells is presented in Figure 16.

Figure 16 Technologies applied in manufacturing of selected solar cells

PV manufacturers using PVD and CVD currently employ sophisticated engineered systems to isolate

hazardous materials from the workplace and to monitor for potential employee exposures. PV devices

based on thin printed films are usually processed in an open-air environment as the printed materials basi-

cally do not exhibit toxicity. Hoverer, there are some exceptions such as devices based on perovskite ma-

terials, which contain lead. Another important aspect of large-scale fabrication of solar cells is the re-

placement of the commonly used hazardous solvents, especially in case of polymer solar cells. These

solvents work well on lab-scale to investigate the fundamental working principles of solar cells. However,

on large-scale, eco-friendly materials are mandatory.

The technology for manufacturing single-, dual- and triple-junction solar cells as well as a-Si, c-Si and

poly-Si photovoltaics is already established. Solar cells manufactured using printing techniques are still

under development and the methods and procedures are not widely available. The concept of nanostruc-

tured Si solar cells is so far only developed at lab-scale.

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References




doi:10.1039/C4EE01223B






doi:10.1038/nphoton.2011.356



doi:10.1002/adma.201304235





475. doi:10.1016/j.solmat.2008.12.012



Nano, 8(10), 10507–10516. doi:10.1021/nn503884z





applications. Solar Cells. John Wiley & Sons, Ltd. Retrieved from

http://books.google.com/books?hl=en&lr=&id=SvVYBK6YAxAC&oi=fnd&pg=PR15&dq=Thin+F

ilm+Solar+Cells+Fabrication+,+Characterization+and+Applications&ots=09tFzNJp-2&sig=M-

DnhFcSWPMFuDJwinaAPm4_J3s\nhttp://books.google.com/books?hl=en&lr=&id=SvVYBK6YA

xAC&oi=fnd&pg=PR15&dq=Thin+film+solar+cells:+fabrication,+characterization+and+applicatio

ns&ots=09tFzNJq-5&sig=Y7weu4Yw4d3ZN_UcjU-sgVHAPNo




You, J., Dou, L., Yoshimura, K., Kato, T., Ohya, K., Moriarty, T., … Yang, Y. (2013). A polymer tandem



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doi:10.1039/C4EE01223B






doi:10.1038/nphoton.2011.356



doi:10.1002/adma.201304235





475. doi:10.1016/j.solmat.2008.12.012



Nano, 8(10), 10507–10516. doi:10.1021/nn503884z





applications. Solar Cells. John Wiley & Sons, Ltd. Retrieved from

http://books.google.com/books?hl=en&lr=&id=SvVYBK6YAxAC&oi=fnd&pg=PR15&dq=Thin+F

ilm+Solar+Cells+Fabrication+,+Characterization+and+Applications&ots=09tFzNJp-2&sig=M-

DnhFcSWPMFuDJwinaAPm4_J3s\nhttp://books.google.com/books?hl=en&lr=&id=SvVYBK6YA

xAC&oi=fnd&pg=PR15&dq=Thin+film+solar+cells:+fabrication,+characterization+and+applicatio

ns&ots=09tFzNJq-5&sig=Y7weu4Yw4d3ZN_UcjU-sgVHAPNo




You, J., Dou, L., Yoshimura, K., Kato, T., Ohya, K., Moriarty, T., … Yang, Y. (2013). A polymer tandem



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Piezoelectric

Brief description

Piezoelectric energy harvesting devices are often based on either a cantilever design or a surface design.

In the first case the d31 piezoelectric coefficient is of interest and in the latter case the d33 piezoelectric

coefficient, where the first subscript indicates polarization direction and the second subscript indicates

direction of the stress. An applied mechanical stress causes the piezoelectric material to generate a short

voltage pulse (on the order of milliseconds). The devices can be resonant, non-resonant or rotational de-

vices/operation modes.

Table 8 lists some of the most common piezoelectric materials, mainly piezoceramics (that are polarized

ferroelectric ceramics [26]), such as PZT [30] and barium titanate [31]. Out of them, Anton and Sodano

[32] and Shen and colleagues [33] report PVDF polymer and micro-fiber composites (MFC) as highly

flexible materials. MFCs are composites that combine the energy density of piezoceramic materials with

the flexibility of epoxy [34]. In [33], the authors compared PZT with PVDF and MFC, they showed that

although PZT shows the highest power density, it is not well suited for high g-vibrations because of its

lower yield strength that results in lower robustness, leading to fracture. Furthermore, zinc-oxide (ZnO) is

an interesting material that is pushing the piezoelectric field to a nanometric scale. It is used to grow one

dimensional hair-like nanowires, with diameters in the sub-one hundred nanometer scale and lengths

ranging from several hundreds of nanometers to a few centimeters. Zinc exhibits both semiconductor and

piezoelectric properties, it is relatively biosafe and biocompatible, so it can be involved in biomedical

applications with little toxicity [35]. In [36] a strain coefficient of ~10 pC/N was reported for zinc oxide

nanowires.

In order to attain piezoelectric effect (in the case of piezoceramics) the polycrystal is heated to the Curie

point along with strong electric field (on the order of 10 MV/m).

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Table 8 Piezoelectric coefficients for various materials

Power/Energy output

Table 9 below shows power output in watts per volume for different piezoelectric resonant devices and

also the load resistance used in the measurements, thus voltage and current can be calculated. Power is

generated in pulses based on the frequency of the external stimuli of the device. The power factor pre-

sented in the rightmost column of the table is a way to compare the devices normalized with the input

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acceleration.

Table 9 Piezoelectric device performance

Table 10 shows examples of materials used in different applications, including dimensions, power and

energy/power density [3].

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Table 10 Examples of piezo devices

Energy input

Conversion of mechanical to electrical energy. Frequency and amplitude of external force are important

factors in terms of how much power that can be generated. In the table above frequencies are reported in

the range from 100 to 107 Hz.

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It has been found that accelerations of 2.5 m/s2 at 120 Hz are typical of many low level vibrations [4].

Form factor

Range from ZnO nanowires and ZnO nanoribbons and up. Thickness can be limited by the polarization

electric field strength required for thicker devices. Too thin devices can also experience shortcuts when

poling, thus limiting the strength of the electric field that can be used which will lower the piezoelectric

coefficient of the device. Two common designs are cantilever and thin surface, where the latter is compat-

ible with printing and a thin flexible format.

Figure 17 Examples of devices. Left to right, top to bottom: THin layer UNimorph DrivER (THUNDER), Active Fiber

Composite, MacroFiber Composite, Radial Field Diaphragm, QuickPack, Bimorphs [4].

Sohn et al. have investigated the feasibility of using PVDF films of thickness 9–110 μm for powering the

Bio-MEMS using the FE analysis package MSC/NASTRAN. The results showed that square (cross-

section—10×10 mm2, thickness=28 μm) and circular (radius=5.62 mm, thickness=28 μm) piezo-films

when stressed under pressure of 5333 N/m2 (or 5,333 mN/mm2) at 1 Hz frequency produce electrical

power levels of 0,25 and 0,33 μW, respectively. This result showed the possibility of utilizing the piezo-

films for powering the DNA telecommunications chip implanted in the human body which requires total

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power of 10 mW. Based on the normal blood flow conditions it was found that a time period of 8–10 h

will be required for one complete operation. PVDF has the advantage that it is mechanically strong, is

resistant to wide variety of chemicals, including acids and it can be manufactured on a continuous reel

basis. However, PVDF has a relatively low value of d31 (3,3×10−11 pC/N) resulting in lower power.

This prompted research on electrostrictive polymers where it is possible to induce large piezoelectric

effect by applying high DC bias field due to Maxwell stress. Electrostrictive polymers recently have been

discovered that generate large strain (above 5%) under moderate electric field intensity (400–800 V on a

20 μm film). Poyl(vinylidene fluoride-trifluoroethylene), or P[VDF:TrFe] copolymers have been shown

to exhibit d31 of 8,0×10−11 pC/N, and polyurethane has d31 of 1,7×10−10 pC/N. A theoretical investiga-

tion conducted by Liu et al. has shown that the energy densities of the order of 0,221 J/cm3 is possible in

the constant field condition using polyurethane material. In future it is expected that the piezoelectric and

electrostrictive polymers will assume significant importance owing to their flexible nature which allows

integration with almost any structure [4].

MicroGen (microgensystems.com) commercializes a 1 cm2 piezogenerator that outputs 58 uW for a 100

Hz input and 900 uW for 600 Hz.

Cost

There are several challenges remaining in the implementation of the low profile piezoelectric energy har-

vesting system including (1) power density (power per unit volume of total device structure), (2) reliabil-

ity (maximum number of cycles before mechanical or electrical breakdown), and (3) costeffectiveness

(total dollar cost for fabrication and installation of the system). The major factor which hinders the im-

plementation of energy harvesting devices in practical applications is higher cost as compared to that of

batteries. As the research in this area continues it will be important to realize scenarios where the high

cost of energy harvesting devices could be overlooked [4].

Figure 18 Costs for different energy sources

Figure 18 above shows an estimated cost of implementing a piezoelectric harvesting system in California

roadways. The estimate is prepared for the California Energy Commission by an independent organiza-

tion (DNV KEMA). The estimated cost is also compared to vendor claims and other energy sources [5].

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Production

Mainly ceramic materials used, but PVDF and ZnO can possibly be used in printed electronics. Ceramic

microparticles can be mixed in polymer binder and then be screen printed. A device based on PZT parti-

cles in polymer binder was manufactured by screen printing and curing at 130 degrees Celsius [2].

The major benefits of using printed electronics is the low production cost and the flexible substrates. A

limitation for using printed electronics could be that some device configurations are cantilever designs.

This could be difficult to produce using only printing techniques. The easiest way to bypass this is to put

the emphasis on producing simple devices, i.e. surfaces. In some cases the cantilever design might also be

possible to produce.

Environment

One of the most popular materials used is PZT (lead zirconium titanate) which contains lead.


Piezoceramics are widely used today, but mainly for other applications than energy harvesting. Though

piezoelectric energy harvesting has been thoroughly investigated since the late 1990s, it still remains an

emerging technology and critical area of interest. Energy harvesting application fields so far mainly fo-

cused on low power devices due to their limited transduction efficiencies.

To date, researchers are following distinct ways in developing piezoelectric energy harvesting technolo-

gy. New materials, configuration approaches and operating modes are under study, and some of these

valuable solutions were proposed in order to achieve large bandwidth harvesters that are able to scavenge

energy from diverse environments.

Resonant cantilever beams need optimization, but several interesting solutions and approaches that were

published can push forward the research. Harvesters are still too complex to be fabricated, but exhibit

great potential.

Considering nanoscale harvesters, they represent a promising but still emerging technique that requires to

be consolidated. Non-resonant solutions, as well as frequency tuning methods, are powerful instruments

to push forward the growth of vibration harvesting techniques. However, though several non-resonant

solutions were demonstrated, new roads can be explored. As an example, in electromagnetic vibration

harvesting a well-known technique to achieve bistability involves mechanical bumpers. Furthermore, all

these piezoelectric harvesting research branches could be merged. Likely, a bistable harvester involving a

high efficiency material, equipped with a proper conditioning circuitry, would achieve significant results.

The limit in terms of harvested energy density has still to be overcome. This has been the main technolog-

ical challenge so far. A well-integrated roadmap was designed in the framework of the Guardian Angels

Coordination Action within the Future and Emerging Technologies Flagship initiative funded by the

European Commission. In this framework, research efforts are focusing on the transducer and also on

the integration with the downstream conditioning circuitry, power management circuits and applica-

tion devices.

Below are some circuit solutions for piezoelectric energy harvesting shown. The circuits without

inductors have a possibility to be accomplished by printing technology, while the inductance of a

printed coil is limited to small values (~H) due to the inherent two-dimensionality of a printed de-

vice.

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References

Caliò, R. et al. Piezoelectric Energy Harvesting Solutions. Sensors 2014, 14, 4755-4790;

doi:103390/s140304755

Note: References marked "[ref x]" in text are cross-referenced to the review article mentioned above.

[2] Almusallam, A. et al. Screen-printed piezoelectric shoe-insole energy harvester using an improved

flexible PZT-polymer composites. PowerMEMS 2013, Journal of Physics: Conference Series 476.

doi:10.1088/1742-6596/476/1/012108

[3] Cook-Chennault et al. Piezoelectric Energy Harvesting: A Green and Clean Alternative for Sustained

Power Production. Bulletin of Science, Technology & Society, Vol 28-6. 2008. pp 496-509. doi:

10.1177/0270467608325374

[4] Shashank, P. Advances in energy harvesting using low profile piezoelectric transducers. J. Elec-

troceram (2007) 19:165-182. doi: 10.1007/s10832-007-9043-4

[5] Hill, Davion, Nellie Tong, (DNV KEMA). 2013. Assessment of Piezoelectric Materials for Roadway

Energy Harvesting. California Energy Commission. Publication Number: CEC-500-2013-007.

Pyroelectricty

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Brief description

Similar to the charge generation in piezoelectric materials, a pyroelectric material generates charge when

exposed to a temperature change. This is described by equation (1) below which defines the relationship

between pyroelectric charge (Q), generated current (ip), rate of temperature change (dT/dt), surface area

of the material (A) and pyroelectric coefficient (p) under short circuit conditions with electrodes that are

orientated normal to the polar direction.

𝑖𝑝 =𝑑𝑄

𝑑𝑡= 𝑝𝐴

𝑑𝑇

𝑑𝑡 (1)

The pyroelectric coefficient of an unclamped material, under a constant stress and electric field, is defined

by eqn (2),

𝑝𝜎,𝐸 = (𝑑𝑃𝑠

𝑑𝑇)

𝜎,𝐸 (2)

where Ps is spontaneous polarization and subscripts σ and E correspond to conditions of constant stress

and electric field respectively. While the pyroelectric coefficient is a vector quantity, the electrodes that

collect the charges are often normal to the polar direction and so the measured quantity is often treated as

a scalar. To maximize the pyroelectric current under short-circuit conditions, clearly the pyroelectric

should have a large surface area, large pyroelectric coefficient and a high rate of temperature change. Eqn

(1) implies that the generated current (but not necessarily power) is independent of thickness and propor-

tional to area since the current is simply associated with the surface charge. By integrating eqn (1) with

respect to time, the net charge developed due to a temperature change (T) is:

𝑄 = 𝑝𝐴∆𝑇 (4)

As pyroelectric materials are typically dielectric in nature, the equivalent capacitance (C) is given by:

𝐶 =𝐴𝜀33

𝜎

ℎ (5)

where 𝜀33𝜎 is the permittivity in the polarization direction at constant stress. The open circuit voltage (V)

and electric field (Efield) developed across the electrodes, from Q = CV, can be expressed as:

𝑉 =𝑝

𝜀33𝜎 ℎ∆𝑇 (6)

𝐸𝑓𝑖𝑒𝑙𝑑 =𝑝

𝜀33𝜎 ∆𝑇 (7)

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It can be seen from eqn (6) that the voltage developed across the electrodes is influenced by the thickness

of the material (h) and is invariant with respect to the area of the electrodes. Since the total energy (E)

stored in a capacitor is 1/2CV2, this represents the amount of energy stored in the material at the end of

the temperature change and is expressed as:

𝐸 =1

2

𝑝2

𝜀33𝜎 𝐴ℎ(∆𝑇)2 (8)

Power/Energy output

Figure 19 shows (a) Ashby diagram for relevant materials properties. Ferroelectric indicated by solid

circles and non-ferroelectric are open-circles, (b) examples of heat source temperatures and harvested

energy for a variety of materials. As pyroelectric devices typically operates at frequencies below 1 Hz an

indication of the upper limit of power generated can be estimated by replacing the mJ/cycle with mW.

A pyroelectric generator based on PZT thin film (175 µm thick, 21 mm length, 12 mm width) exhibited a

pyroelectric coefficient of approximately -800 µC/m2 K1. For a temperature change of 45 K at a rate of 0,2

K/s the output open-circuit voltage and short-circuit current reached 22 V and 171 nA/cm2, respectively,

corresponding to a maximum power density of 0.215 mW/cm3.

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Figure 19: (a) Ashby diagram showing materials properties. (b) Harvested energy vs temperature.

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Energy input

Pyroelectric materials generate power by temperature fluctuations over time, i.e. dT/dt. Pyroelectric har-

vesters tend to operate at low frequency, typically <1 Hz, due to the slow temperature oscillations in sys-

tems of large thermal mass and heat transfer inertia. Since temperature oscillations are often slow, efforts

to transform a temperature gradient into a time variable temperature include the use of cyclic pumping.

The power consumed by the pumping process can be a relatively small fraction of the harvested energy

(<2%), which can make the process feasible. Naturally occurring temperature changes for harvesting are

rare but examples include changes in ambient temperature, the human body, exhaust gases and natural

temperature variations due to convection and solar energy [ref 36].

Different pyroelectric cycles for energy harvesting exists, e.g. Carnot cycle, resistive cycles, synchronized

electric charge extraction (SECE), synchronized switch damping on inductor (SSDI) and Olsen cycle. The

most efficient is the Olsen cycle, but it’s restricted to operation between two specific temperatures and the

operation cycle is quite complex so it has been mainly considered for larger systems.

Form factor

Macro- to nano-scale. However, complicated cycling schemes (temperature and electric field) have to be

utilized in order to achieve high efficiency which is then limited to larger systems (i.e. not IoT compati-

ble).

Production

PZT films can be screen printed, perhaps curing requires high temperature resistant substrates.


Compared to other forms of energy harvesting and thermal harvesting such as thermoelectric generators,

the use of pyroelectric harvesting to generate electrical energy from temperature fluctuations is less well

studied. While the efficiencies can be high for specific thermal and electric cycles, especially Olsen-based

cycles, the inability to induce high frequency temperature fluctuations currently limits the amount of

power that can be harvested, this is in contrast to mechanical oscillations where mechanical vibrations

over 102 Hz are relatively easy to implement. With regards to potential harvesting cycles, resistively load-

ing the pyroelectric element is relatively simple and can operate in a range of operating environments and

temperatures although the material must clearly maintain its polarized nature. The use of natural tempera-

ture fluctuations to generate a pyroelectric current as surface charges are released on heating a pyroelec-

tric is generally of low efficiency. Other methods, such as employing the Olsen thermal cycle with corre-

sponding changes in capacitance and material phase changes can increase both the efficiency and the

quantity of the power generated compared to simple resistive loading. Such systems are often designed to

operate within specific temperatures and electric field ranges and as a result Olsen-type systems tend to

be designed to operate in specific locations and manufactured from bulk materials for larger-scale har-

vesting systems, rather than low power systems for wireless sensor systems. Limited systems have em-

ployed the Olsen-type cycle at the micro to nano-scale. In an effort to improve power capability attempts

to increase the operational frequency are often undertaken, such as the generation of mechanical oscilla-

tions from a temperature gradient. The creation of pyroelectric harvesting materials and systems at the

nano-scale may also offer opportunities for operation at higher frequencies. This can be coupled with the

development of new materials with improved pyroelectric coefficients especially for harvesting applica-

tions. Materials and material architectures with improved heat transfer are of interest to increase rates of

temperature change or improved FOMs. Composite material systems or design of materials with high

FOM to tune the pyroelectric response and mechanical and thermal properties are also potential future

avenues of research. Since the pyroelectric effect originates from spontaneous polarizations within the

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material, all pyroelectric materials are also piezoelectric, therefore hybrid pyro-piezo harvesting systems

are of interest. In the design of such systems care must be taken to ensure both harvesting mechanisms are

working in phase to enhance power generation. Novel systems that use thermal fluctuations or thermal

gradients to generate a mechanical stress to enhance the secondary or tertiary pyroelectric coefficients are

also of interest.

The low efficiency of resistive and synchronised electric charge extraction cycles and low frequency of

operation may often result in pyroelectric harvesting being a less favourable harvesting option compared

to vibration harvesters or photovoltaics for low power applications. However in locations with low levels

of mechanical vibrations or light it is an intriguing option to generate useable power. It can also be used

to enhance the power generation capability of mechanical energy harvesting systems.

References

C.R. Bowen et al. Pyroelectric materials and devices for energy harvesting applications. Energy Environ.

Sci., 2014, 7, 3836; doi:10.1039/c4ee01759e

RF-harvesting

Brief description

RF-harvesting can use either ambient RF-energy or dedicated energy sources. This summary will focus

on the available “energy density” to be able to judge whether RF-energy harvesting is a viable technique

to power a certain IoT-application. In general an RF-energy harvesting circuit have these basic compo-

nents. (Figure 20 from ref [3]). The available output power will depend on all three components; antenna,

matching network, voltage multiplier.

Figure 20 Schematic RF-harvesting circuit

Power/Energy output

Available power is in the W/cm2 range as an average power density in an urban environment. From a

dedicated RF-source, like a NFC-reader in a mobile phone, approximately 200 mW can be generated in

the near-field.

Energy input from Ambient RF-energy

Pinuela et al [1] have studied the conditions for RF-harvesting from ambient sources in an urban envi-

ronment (London). They have excluded inductive or near-field powering, leaving only radiative harvest-

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ing. The largest RF contributors are found in five frequency bands within the ultrahigh frequency (0.3–3

GHz). The sources are DTV, GSM900, GSM1800, 3G and Wifi. Contributions from 4G could probably

be an additional source but is not detected in this work which was done 2012. New results are not availa-

ble at www.londonrfsurvey.org, but no thorough search has been done. The power levels was measured

during daytime, 10-15. The power spectrum shown in Figure 21 shows the contributions. The power den-

sity is denoted in dBm/cm2, where 0 dBm corresponds to 1 mW. This gives for example -60dBm = 1 nW.

Figure 21 Ambient RF power spectrum

The table below shows average and maximum power density in the different frequency bands.

One can note that the being close to a mobile base station is favorable since the base transmit (BTx) is

always larger than mobile transmit (MTx). Since these measurements are done outdoors the Wifi-

contribution is likely to be larger indoors.

At the locations with largest power density the following numbers were recorded.

http://www.londonrfsurvey.org/

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Here one can see that power levels approaching W/cm2 seems to be available.

As a comparison the maximum allowed power levels from a health perspective can also be studied. The

maximum exposure levels to the public [2] in the frequency range 10 MHz- 2 GHz is 2-10 W/m2 = 200 –

1000 W/cm2 . At power levels in the range 5-60 mW/cm2, a prolonged exposure has been shown to in-

duce damage in rabbit’s eyes. The conclusion is that power densities exceeding hundreds of W/cm2 is

not realistic for the general public.

Even though the power levels are low, enough power can be harvested to power simple electronic cir-

cuits. Examples in [3] reports power in the range 10-100 W from ambient sources (e.g. TV-tower)

Energy input from Dedicated sources – RF near-field

Near Field Communication (NFC) is one example where a dedicated source can be used to power an elec-

tronic circuit. In a study conducted by Univ. Washington and Intel [4] it was shown that a mobile phone

NFC reader can give an output of 200mW at 13,56 MHz. In a dedicated receiver circuit it was possible to

harvest 17 mW (12.3 mA at 1.44 V).

RFID readers have 3-4 W maximum power radiated. If this could be used in a practical application is

unknown and needs further investigation.

Form factor

The form factor will typically be determined by the antenna size. At low frequencies (e.g. 13,56 MHz) a

larger coil will give a larger power input. At higher frequencies (UHF) the antenna will probably be a

half-wave dipole antenna, with size determined by the frequency.

Cost

The better antenna, matching network and rectifier you have the better energy harvesting you can get.

E.g. the diodes in a charge pump circuit will benefit from a low forward voltage drop. Better components

will increase the cost.

Production

Antennas with Rs below 50 mOhm/sq is probably needed, i.e. metallic. Printed Ag or Cu could be possi-

ble. Rectifying diodes operational in the GHz region will be needed.

This means that printed components (diodes and capacitors) probably could be used in these circuits.


The technology is available today with traditional electronics and antennas. It is important to explore in

more detail how much printed components and antennas could be used for this purpose.

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References

1. Manuel Piñuela, Paul D. Mitcheson, and Stepan Lucyszyn, Ambient RF Energy Harvesting in

Urban and Semi-Urban Environments, IEEE TRANSACTIONS ON MICROWAVE THEORY

AND TECHNIQUES, VOL. 61, NO. 7, JULY 2013.

2. RADIATION PROTECTION STANDARD - Maximum Exposure Levels to Radiofrequency

Fields — 3 kHz to 300 GHz. Australian Radiation Protection and Nuclear Safety Agency. 2002.

3. Ufuk Muncuk, “Design optimization and implementation for RF energy harvesting circuits.”

Thesis at Northwestern University, 2012.

4. Artem Dementyev et al., Wirelessly Powered Bistable Display Tags, Proceedings from

UbiComp’13, September 8–12, 2013, Zurich, Switzerland.

Fuel cells

Brief description

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical

reaction with oxygen or another oxidizing agent. There are many types of fuel cells, but they all consist of

an anode, a cathode and an electrolyte that allows charges to move between the two sides of the fuel cell.

Electrons are drawn from the anode to the cathode through an external circuit, producing direct cur-

rent electricity. As the main difference among fuel cell types is the electrolyte, fuel cells are classified by

the type of electrolyte they use followed by the difference in startup time ranging from 1 second

for proton exchange membrane fuel cells (PEM fuel cells, or PEMFC) to 10 minutes for solid oxide fuel

cells (SOFC). Fuel cells come in a variety of sizes. Individual fuel cells produce relatively small electrical

potentials, about 0.7 volts, so cells are "stacked", or placed in series, to increase the voltage and meet an

application's requirements. Fuel cells come in a variety of sizes. Individual fuel cells produce relatively

small electrical potentials, about 0.7 volts, so cells are "stacked", or placed in series, to increase the volt-

age and meet an application's requirements. In addition to electricity, fuel cells produce water, heat and,

depending on the fuel source, very small amounts of nitrogen dioxide and other emissions. The energy

efficiency of a fuel cell is generally between 40–60%, or up to 85% efficient in cogeneration if waste heat

is captured for use.

In general a fuel cell needs a handling system for the fuel, in gas or liquid form. Often a supply of hydro-

gen gas or a generation of hydrogen from another source close to the fuel cell needs to be obtained. The

requirements for handling H2 gas is not readily compatible with printed flexible devices and has not been

further investigated here.

Electrical generators

Brief description

The energy generated through wind, geothermal, nuclear, wave or coal is generated electromechanically.

Generators are indeed the backbone of the electric power grid. Alternators and dynamos achieve efficien-

cies around 90%. Compared to a thermodynamic limit of 37% for internal combustion engines and a more

realistic efficiency of 20%.

Piezoelectric generators have been demonstrated with up to 70% efficiency. They are printable and well

suited for miniaturization. However, they might not be used in shielded environments and applications

where a noise is undesirable.

A wankel engine MEMS has also been demonstrated.

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Electrolyte

http://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cell

http://en.wikipedia.org/wiki/Solid_oxide_fuel_cell

http://en.wikipedia.org/wiki/Solid_oxide_fuel_cell

http://en.wikipedia.org/wiki/Nitrogen_dioxide

http://en.wikipedia.org/wiki/Cogeneration

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Proper electric generators (rotor/stator configuration) are not compatible with printing techniques. Mi-

cromachining them is possible but would cost too much.

Power/Energy output

- 0.278 mW for millimiter sized thin film (harvesting a 1.2 mm in plane 20 Hz oscillation). Tsutsumino et

al. PowerMEMS 2006.

Energy input

Ambient vibrational energy.

Mechanical energy

Form factor

Alternators are harder to shrink because of the moving parts.


Demonstrators commercially available.

References

A Millimeter-Scale Electric Generator. Senesky, IAS, 2004

Invited talk, IEEE Int. Symp. Micro-NanoMechatoronics and Human Science (MHS2008), Nagoya,

(2008), pp. 180-183.

Micro Seismic Electret Generator for Energy Harvesting, T. Tsutsomino, PowerMEMS2006

http://www.microgensystems.co/default.asp

Microfibre-nanowire hybrid structure for energy scavenging, Qin, Nature 2008

Thermo Electric Generators

Thermoelectric generators are devices that convert heat into electrical energy. The device requires a tem-

perature difference and the physical phenomenon used is the Seebeck effect. The table below shows vari-

ous material systems used for TEGs and their performances. A general challenge when building a TEG-

system is to find materials with high electrical conductivity and low thermal conductivity.

http://www.microgensystems.co/default.asp

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References

1. Kouji Suemori, Satoshi Hoshino, Toshihide Kamata, Flexible and lightweight thermoelectric generators com-

posed of carbo nnanotube–polystyrene composites printed on film substrate, Appl. Phys. Lett. 103, 153902

(2013)

2. Ju Hyung We, Sun Jin Kim, Byung Jin Cho, Hybrid composite of screen-printed inorganic thermoelectric film

and organic conducting polymer for flexible thermoelectric power, Energy 73 (2014) 506-512.

3. Sun Jin Kim, Ju Hyung We and Byung Jin Cho, A wearable thermoelectric generator fabricated ona glass fab-

ric, Energy Environ. Sci., 2014, 7, 1959–1965

4. Qingshuo Wei,* Masakazu Mukaida,* Kazuhiro Kirihara, Yasuhisa Naitoh and Takao Ishida, Polymer ther-

moelectric modules screen-printed on paper, RSC Adv., 2014, 4, 28802–28806

5. Ziyang Lu , Michael Layani , Xiaoxu Zhao , Li Ping Tan , Ting Sun , Shufen Fan , Qingyu Yan , Shlomo Mag-

dassi , and Huey Hoon Hng, Fabrication of Flexible Thermoelectric Thin Film Devices by Inkjet Printing,

small 2014, 10, No. 17, 3551–3554

Supercapacitors

Brief description

A supercapacitor is a device used to store electrical charge and energy similar to that of a battery. It com-

prises two electrodes with electronic conductive materials separated by an ion conductor (electrolyte).

CNT–polystyrene composite

PEDOT:PSS and inorganic thermoe-lectric film

Bi2Te3 (n-type) and Sb2Te3 (p-type)

PEDOT:PSS Sb 1.5 Bi 0.5 Te 3 and Bi 2 Te 2.7 Se 0.3

Nanoparticles

Power/Energy output

55 mW/m2 at a ΔT of 70

output voltage of 85.2 mV, 1.2 mW cm-2 at a 50 K 12.1 mV at 5k

141 mV K-1 and 98 mV K-1, 3.8 mWcm-2 and 28 mW g-1 at a ΔT= 50 K, 120 cycles

18 mV K-1 and 25 mWm-1 K-2, at 25 25 mV K-1 and 34 mWm-1 K-2 at 200 .

at 100 for over 100 h without any encapsulation

341 ± 4 μV/K at 50 , 77 μWm −1 K −2 at 75 °C

Energy input heat Body heat (poten-tially)

Body heat heat heat

Form factor composed of 1985 individual thermoelectric devices, each being 1.5mm wide, 0.8mm long, and 0.15mm thick

40 μm thickness 500 μm thick-ness fabric No restriction for area 0.13 g cm-2

Substrate: 300 μm thick paper; PEDOT:PSS layer: 20-30 μm thick

Substrate: 30-50 mm Material: 150 layers

Production Print and deposite screen-printed, spin-coating and infiltration process.

screen printing printing Ink-jet printing

Environment No specific need No specific need No specific need

High humidity and high temperature

High temperature

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The electrodes usually comprise a porous material with large specific surface area and a current collector.

The electrode typically has an ion-permeable separator membrane that prevents electrical short circuit.

Figure 22 Cross section of a supercapacitor with the electric field distribution (left) and a wide range of commercial su-

percapacitors (right) [7].

There are two classes of supercapacitors: Electric Double Layer Capacitors (EDLCs) and Pseudocapaci-

tors. The EDLC uses only electrostatic storage over a large area (porous) electrode. The pseudocapacitor

uses a redox reaction with capacitor like characteristics. EDLCs are often based on carbon while pseudo-

capacitors can be based on conductive polymers. Figure 23 shows the different types.

Another class of materials that can be used for supercapacitor applications are metal oxides.

Figure 23 Different classes of capacitors [7]

Device specifications

Function Supercapacitor Lithium-ion (general)

Charge time 1–10 seconds 10–60 minutes

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Cycle life

Cell voltage

Specific energy (Wh/kg)

Specific power (W/kg)

Cost per Wh

Service life (in vehicle)

Charge temperature

Discharge temperature

1 million or 30,000h

2.3 to 2.75V

5 (typical)

Up to 10,000

$20 (typical)

10 to 15 years

–40 to 65°C (–40 to 149°F)

–40 to 65°C (–40 to 149°F)

500 and higher

3.6 to 3.7V

100–200

1,000 to 3,000

$0.50-$1.00 (large system)

5 to 10 years

0 to 45°C (32°to 113°F)

–20 to 60°C (–4 to 140°F)

Typical values of commercial supercapacitors compared to lithium-ion batteries [10].

Electrode materials

Refrences: [1, 2, 3 ,4, 5].

Carbon:

Specific capacitance: 100-500 F/g

Power density: ~100 kW/kg (sprayed carbon nanotubes)

Energy density: ~10 Wh/kg (sprayed carbon nanotubes)

Area specific capacitance: ~30 mF/cm2 (~10µm thick sprayed carbon nanotube electrodes)

Cycle life: ~1,000,000

Carbon is the most commonly used material in commercial supercapacitors, largely due to its low cost.

Activated carbon is often used, but also carbon nanotubes, graphene, nanoporous carbon and carbon aero-

gels has been investigated as the electrode material.

Conductive polymers:

Specific capacitance: 50-150 F/g (PEDOT); <400 F/g (Polypyrrole); <480 F/g (PANI)

Cycle life: 1,000-10,000

Conductive polymers typically have shorter lifetime in supercapacitors due to the large volume changes

that occur during the charging cycle. They are typically more expensive than carbon electrodes.

There are no/few commercial supercapacitors based on conductive polymers.

Metal oxides:

Specific capacitance: 50-1300 F/g (RuO2); 140-1300 F/g (MnO2)

Although there has been a lot of research on metal oxides in supercapacitors there are no/few commercial

examples. Metal oxides are more expensive than carbon which is one possible reason for why they are

rarely used. Another reason is that many metal oxides (such as MnO2) have low conductivity which re-

sults in large ESR-values for thick films. The high capacitance values reported in literature is often the

result of thin metal oxide layers.

Electrolytes

References: [6, 8, 9].

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Many of the properties of a supercapacitor are highly dependent on the choice of electrolyte. The electro-

lyte limits the electrical potential window to <4V. At higher voltages the devise will degrade due to elec-

trochemical reactions. This can be due to electrode degradation or the production of gases at the elec-

trode. With aqueous electrolytes the capacitors typically operate at voltages below 1V. With organic elec-

trolytes the capacitors can operate up to 3.5V. With ionic liquids it is possible to reach even higher volt-

ages (4-6 V or higher). However, due to the hygroscopic nature of ionic liquids they will quickly absorb

water when exposed to ambient conditions which will lower the electrochemical window.

The electrolytes can be in liquid, gel or solid form. Supercapacitors with liquid electrolytes often suffer

from leakage-problems. A polymer matrix filled with a solvent with a solvated salt can comprise a gel

electrolyte. Polyelectrolytes are similar to gel electrolytes but have fixed ionic groups along the polymer

backbone.

The choice of electrolyte also influences the temperature- and humidity-limitations of the capacitor. Typi-

cally a supercapacitor with an organic electrolyte can operate between -40 and 70°C, although the per-

formance can vary considerably over this range. By using ionic liquids it is possible to make supercapaci-

tors operating at up to 200°C. The performance can also be influenced by humidity if the device lacks

sufficient barriers.

The equivalent series resistance (ESR) of a supercapacitor is highly dependent on the choice of electro-

lyte. A small ESR is desirable since it maximizes the current density and minimizes losses. The more ions

that can be solvated into a certain solvent the lower the ESR will be. Aqueous electrolytes can solvate

ions better than most organic solvents and typically have an ionic conductivity between 100 and 1000

mS/cm. Organic solvents are typically in the range 10-60 mS/cm. Solid electrolytes has lower conductivi-

ty than liquid electrolytes but are less prone to leakage. With a solid electrolyte it is possible to omit the

separator membrane.

The prize of most commercially available ionic liquids is in the range of $100-$10,000 per kilogram. The

large cost is mainly due to small-scale production. With increasing demand on ionic liquids the prize is

going down. In 2014 the cost of some ionic liquid, produced in large quantities, was down to $1/kg.

Electrolyte type Electrochemical window

Conductivity Temperature range Cost

Aqueous 1.2V 100-1000 mS/cm -40 - 70°C Low

Organic 3.5V 10-60 mS/cm 0 - 70°C Low

Ionic liquids 6V 1-70 mS/cm -60 - 200°C High (but dropping)

Table 11 Comparison between different types of electrolytes.

Form factor

Carbon and polymer based supercapacitors has no limiting dimensions. For flexible supercapacitors the

carbon layers are typically 10-100µm thick [11]. Metal oxides are best suited for thin-film supercapaci-

tors [1]. Density: 0.5-2 g/cm3 (activated carbon); ~1g/cm3 (conductive polymers)

Cost

$20 (typical value of commercial supercapacitors) [10].

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Production

The layers comprising a supercapacitor are usually laminated together and then rolled up and put in a

container. Electrodes of carbon and conductive polymers can be printed onto flexible collector electrodes

(such as aluminum coated PET). Metal oxide particles can be mixed with a carbon ink or a polymer to

become printable. Fully printable capacitors (no lamination) have also been realized. This is easiest done

with a lateral structure [5, 11].

Figure 3: Laminated supercapacitor with printed electrodes [11].

The table below contains an example of specifications for flexible supercapacitors with printed electrodes

produced by VTT Technical Research Centre of Finland [11]:

Printed supercapacitors

Electrodes: Aluminum coated PET with 10-20 µm graphite followed by 70-90 µm activated carbon

Electrolytes: Liquid/solid, Aqueous/organic/ionic liquids

Area specific capacitance: 25-125 mF/cm2

Operating voltage: 1.2V (aqueous electrolyte) and 2.7V (organic electrolyte)

Current density: 2.5-12.5 mA/cm2

Leakage current density: ~2.5 µA/cm2

Shelf life: 10 years with proper sealing

Cycle life: 40,000-60,000 (aqueous electrolyte) and >100,000 (organic electrolyte)

Environment

Nanomaterials such as carbon nanotubes, graphene nanosheets and metal oxide nanoparticles as well as

certain solvents used in organic electrolytes can be toxic/carcinogenic and environmentally hazardous.


There are many commercially available supercapacitors. Many of them based on carbon, such as activat-

ed carbon or carbon aerogels. Graphene and carbon nanotubes are close to commercial applications.

Much research is done on composites between carbon, conductive polymers and metal oxides.

References

[1] Guoping Wang, Lei Zhang and Jiujun Zhang, Chem. Soc. Rev., 2012,41, 797-828 .

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[2] Shen-Ming Chen, Rasu Ramachandran , Veerappan Mani , Ramiah Saraswathi, Int. J. Electrochem. Sci., 9

(2014) 4072 – 4085.

[3] Zenan Yu, Laurene Tetard, Lei Zhai and Jayan Thomas, Energy Environ. Sci., 2015, Advance Article.

[4] Milana Lisunova, Yuliya Lisunova, Sora Lee, Jaemyung Kim, Kyunam Joo,Yoonjin Kim, Dongsik Zang,

Heesung Moon, C A R B O N ,47 (2009) 1119-1125.

[5] Martti Kaempgen , Candace K. Chan , J. Ma ,Yi Cui and George Gruner, Nano Lett., 2009, 9 (5), pp 1872–1876.

[6] Raquel S. Borges, Arava Leela Mohana Reddy, Marco-Tulio F. Rodrigues, Hemtej Gullapalli, Kaushik Bala-

krishnan, Glaura G. Silva & Pulickel M. Ajayan, SCIENTIFIC REPORTS, 2013, 3 : 2572

[7] Supercapacitors: http://en.wikipedia.org/wiki/Supercapacitor

[8] Ionic liquids: http://en.wikipedia.org/wiki/Ionic_liquid

[9] Long Chen, Mahdi Sharifzadeh, Niall Mac Dowell, Tom Welton, Nilay Shah and Jason P. Hallett, GreenChem.,

2014, 16 ,3098-3106

[10] Commercial supercapacitors: http://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor

[11] “Printed supercapacitors, project report”, VTT Technical Research Centre of Finland, 2014.

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Internet of Things application – three use cases

Monitoring “health” of industrial machinery

Background

Before each mechanical component fails, its operational characteristics changes. It may generate different

sounds (vibrations), increase its temperature (higher friction) or exhibit changes in its working cycle

(slow down or accelerates). The consequence of unnoticing or ignoring that syndromes usually results in

shutting down an entire plant or vehicle immobilization, which may cause serious costs. Therefore, it

seems critical to pinpoint the problems and propose solution before they lead to costly shutdowns.

Many operation crew members still rely on obvious syndromes such as noise or significant increase in

heat of mechanical components. Others implement advanced solutions and smart instrumentation which

unfortunately implies severe costs. Therefore, these smart solutions are targeted at machines ranked as

essential to highly critical only and the weight of each system is ranging between several up to over a

dozen of kilograms.

What we propose here is a lightweight printed sensor tag powered via alternative sources of energy such

as thin film battery, thermoelectric module, piezo element, RF energy harvesting devise or photovoltaics

(outdoor machinery such as wind turbines). Figure 24 demonstrates main concept of sensor tag monitor-

ing temperature and frequency of an electric motor.

Figure 24 Demonstration of a sensor tag concept; the device is adhered to an electric motor

Presented case scenario describes a method of continuous monitoring of the status of critical mechanical

components of machinery, vehicles and plant equipment. Proposed system presented in Figure 25, not

only supplies real-time information on the operational state of mechanical components but also analyzes

characteristics and informs operating crew about replacement needs.

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Figure 25 Operation diagram of the system

Functionality:

1. Real-time information on the operational state (temperature, vibrational frequency) of mechanical

components using display.

2. Notifications (displaying and sending to the hub) in case of needed adjustments or replacements. Im-

plemented electronics automatically associate pre-defined frequency patterns and temperature fluctuation

profile (recorder during label installation) with measured signal and request a specific action in case of

detecting significant change in pattern.

3. Centralized machine-monitoring system provides the ability to monitor large amount of installed de-

vices. It provides a real-time support and troubleshooting if issues arise with a machine. In the event of a

problem, the system notifies operating crew.

Thanks to its low costs and simplicity, system could be applied either at large (e.g. difficult-to-access

plant machinery, wind turbines, pipelines) or small (e.g. an electric engine in a single section of conveyor

belt, pump or valve in industrial process plant) scales devices.

Use case

The proposed application is intended to work in industrial environment or large scale outdoor mechanical

installations (e.g. wind turbines, pipelines). A typical industrial environment contains many sources of

various signals which have potential not only to provide information about such environment, but can

also efficiently power up electronic devices. Signal of interest for proposed system are the following:

vibrations (acoustic),

heat,

solar/light irradiation,

magnetic field,

However, in the same time both industrial and outdoor environment impose many constraints on proposed

system, which are

uncontrolled temperature,

broad range of humidity,

exposure to mechanical damage,

exposure to industrially used gases and sources of light

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Market analysis

Industrial wireless sensors have the potential to be a major contributor to increased efficiency of machine

health monitoring, and the use of harvester-powered industrial wireless sensors represents a huge oppor-

tunity for cost savings and process efficiency improvements.

The total revenue of the global machine health monitoring market is expected to reach $2.50 Billion at a

Compound Annual Growth Rate of 7.16% from 2014 to 2020. 1

Manufacturing companies are increasingly aware of the value of predictive maintenance systems (as op-

posed to reactive and preventive maintenance). So much so that General Electric has acquired a leading

provider of machinery protection and monitoring, Bently Nevada, whose product portfolio comprises

monitoring systems, sensors and transducers, software, test and calibration equipment, custom products,

and more.

Predictive monitoring is normally performed through permanently mounted sensor systems which are

costly to install, and expensive to maintain. Wireless sensors can potentially address this cost issue, by

simplifying sensor installation, reducing maintenance associated with wiring faults, permitting new sensor

locations that would otherwise been inaccessible with wired sensors, and offering greater flexibility in

that sensors can be easily installed, or removed, as required.

There are, however challenges related to battery life and to battery replacement which is an additional

maintenance activity that can offset the savings provided by wireless sensors.

Some examples of current battery-powered solutions show 5-7 years operation with a coin cell battery, or

battery-powered systems that are programmed to skip a measurement in order to conserve battery power.

Some systems boast of “running on a high energy lithium battery with a life expectancy of more than

three years”.

Potential users consider energy harvesting as an interesting solution to one of the challenges facing bat-

tery-powered wireless sensor networks. The development of low power sensors with energy harvesting

technologies is therefore something which Swedish companies such as Siemens Industrial Turbomachin-

ery, Gränges, Electrolux and SKF, are interested in, and all have expressed an interest in possible partici-

pation in future field testing.

Energy budget

As a first case we consider a sensor tag for intermittent sensing, that has one low-power microcontroller

and one Bluetooth (BT) chip. Assumptions about operation:

Sensor readings will be taken at certain intervals. This might vary hugely, from maybe 1 h down

to less than 10 s. We investigate two examples, 1 h and 10 s intervals.

External communication to report readings: Assumed to occur with intervals between 1 min and

24 h. We investigate two examples, 1 min and 24 h intervals.

A low-power microcontroller uses 3V, 150 µA during 1 s to perform a sensor reading. This

equals 450 µJ.

1 Machine Health Monitoring Market by Product (vibration monitoring, thermography, ultrasound emission, lubri-

cating oil analysis, corrosion monitoring, motor current signature analysis), Component, Application and Geography

– Global Forecast to 2014 - 2020

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BT device uses 10-500 mW during 3 ms to send a data package, depending on distance. We as-

sume a rather long distance and a power use of 100 mW. We also assume one data package is

enough to send the needed data. This works out to 300 µJ per transmission event.

In the idle phase, the label (basically the microcontroller) uses 3V, 20 nA. This sums up to 5 mJ

per 24 h.

Summing all these contributions up: we get the following:

Sensing/communication interval of 10 s/1 min uses 4300 mJ for 24 h of operation.

This converts to an average power of 50 µW. Maximum power is 100 mW.

Sensing/communication interval of 1 h/24 h uses 16 mJ for 24 h of operation.

This converts to an average power of 0,2 µW. Maximum power is 100 mW.

An activity level of 20% of the maximum would mean a sensing/communication interval of 50

s/5 min

This converts to an average power of 10 µW. Maximum power is 100 mW.

If energy harvesting is used, and energy is accumulated in a supercapacitor or rechargeable battery, the

capacity of this storage needs to be enough for one sensing operation and one communication event,

which is 450+300 µJ = 750 µJ. With a bit of margin, the storage capacity needs to be 1 mJ.

The printed supercapacitor from VTT (see section about supercapacitors) can store 25 mF per cm2 at a

voltage of 2,7 V, which translates to a stored energy of 91 mJ for a 1 cm2 device. Thus, a really small (a

few mm2) supercapacitor should be able to handle the need in this circuit.

Possible Energy sources

Proposed system could be powered via battery (see Table 12) or one of the following alternative sources

of energy (see Table 13):

thermoelectric module (TEG),

piezo element,

RF energy harvesting devise,

Photovoltaics (outdoor machinery such as wind turbines).

Battery Operation time in

intended

application* type model

(manufacturer)

voltage capacity Operational

temperature

Conventional

“knappcell”

CR2032 3V 220 mAh -20 to 70 °C 7 years

printed Enfucell 3V 10 mAh -35** to 50 °C 4 months

Table 12 Possible battery implementations

*Battery power: 10 µW average power translates to 30 mAh per year with a 3V battery.

** Limited performance below 0.

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Form of energy Energy harvesting

type typical range device available power

vibrations 100 – 300 Hz trapezoid piezoe-

lectric module

20 – 150 W

temperature gradient 20 – 90 C Thermoelectric

module

10-190 µW/mm2

RF frequencies 3 kHz – 300 GHz RF harvesting mod-

ule

10-40 µW

solar/light 300 – 1100 nm Solar cell up to 300 W/m2

Table 13 Possible alternative energy source implementations

A commercially available Bi2Te3-based TEG from Micropelt gives around 0,6 µW/mm2 at T=5 K,

meaning that an area of 17 mm2 would yield the needed 10 µW at 5 K. At T=20 K, output power is 9,6

µW/mm2 and at T=90 K, output power is 194 µW/mm2.

System design

Proposed system presented schematically in Figure 26 is based on traditional electronic components. It

uses sensors that continuously acquire data on vibrational frequency and temperature. After amplification

the signal is provided at the input of microcontroller which store it in a memory, or/and drives the display

(user interface), or/and transfer data to the hub via communication module. Power management module is

responsible for energy harvesting and storage.

Figure 26 Schematic representation of the sensor tag system design

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Manufacturing methods

System can be potentially manufactured using printed techniques (passive circuit elements and sensors)

and hybridized with silicon components (active components such as C, memory, communication module

and power management module) and energy harvesting module.

Research needs

Research that is needed concerns mainly stability testing of components under tough conditions such as

broad range of temperature,

vibrations

broad range of humidity,

exposure to mechanical damage,

exposure to industrially used gases and sources of light

Another aspect of research needed concerns the integration of components on flexible or rigid substrates.

Environmental monitoring (forest monitoring)

Background

Today there is a large interest in early forest fire detection for quick response [1]. There is also an interest

in monitoring the health of forests, for example pH levels or the presence of pollutants in streams or the

ground [2]. Both problems could be solved by wireless sensor networks.

There are existing pilot tests of forest monitoring systems, but the devices used are typically bulky and

require batteries to operate. Therefore, both the number of devices and their lifetime are limited. To min-

imize the response time during forest fires and to get accurate data in environmental monitoring, as high

sensor density as possible is desirable.

Use case

The wireless sensors will be placed in the forest and could be spread over large areas. If a large number of

such sensors are being used, replacing batteries would be difficult due to the remote locations. Therefore,

it would be necessary to harvest energy from the surrounding either to power the device or to prolong the

battery lifetime. The sensor devices would send data to central RF receivers which in turn can send the

signal via GPS to the user.

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Figure 27 Illustration of the forest monitoring system.

Market analysis

Forestry companies are naturally interested in solutions that can help them monitor and detect forest fires.

In general, they are very concerned by the potential risk of fires and are therefore interested in improving

systems of proactive preventive monitoring.

Today forest fire monitoring and detection is primarily done through manual observations - by patrols,

from towers, aircraft, and satellites. Recently various crowdsourcing solutions have been developed,

whereby the general public is able to report fires via smartphone apps and the mobile phone network.

A number of fire monitoring systems using cameras to detect smoke or flames exist, but have not per-

formed successfully in field tests.

There also exist systems that use wireless sensor networks that attempt to detect forest fires, however

there is no common, simple, established method which has proven successful in the determination of

whether or not a fire has started.

A system from Libelium is available commercially, using gas boards to measure temperature, humidity,

carbon monoxide (CO), and carbon dioxide (CO2) as a way of detecting fire. This system can also use

solar panels for power scavenging. However, the system is bulky in size, and has considerable power

consumption, which affects both the ease of installation and the system’s life span.

It is generally agreed that the best available solution for forest fire detection is through the use of smart

wireless sensor networks.

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While wireless networks are considered the future of forest fire detection, the issue of battery life is still a

potential issue for the system. In large-scale deployment it is virtually impossible to go back to each node

in the forest for recharging or battery replacement, this makes the use of energy-harvesting systems a

viable alternative.

Holmen Skog in Norrköping & Örnsköldsvik, and SCA Skog in Sundsvall have both expressed interest in

the development of further research, and are keen to participate in future field testing.

Energy budget

For early fire detection, the detectors need to be continuously operating since a fire can spread large dis-

tances in a matter of minutes. In the case of environmental sensing measuring one a day, once a week or

even once a month might be sufficient. The largest energy consumption is in the wireless signal. Sending

a satellite signal requires around 0.5-5 W. Using a short range RF signal, such as VHF, the power con-

sumption could be cut considerably to around 10 mW [3]. VHF has a maximum detection radius of 10 km

which would require a transmitter every 20 km in the sensor network. This receiver could in turn send the

signals using GPS to the end user. In forest fire detection, the signal need only to be sent once a fire

breaks out. This energy could be stored in a battery while the continuous operation of the sensor could be

powered by surrounding energy. Another possibility is to have the heat from the fire generate all the nec-

essary energy which will activate the device and send a signal. This could be done with pyroelectrics or

thermoelectrics. Environmental monitoring requires a signal to be sent at regular time intervals. This en-

ergy could be harvested between transmissions and stored in a supercapacitor to be used when needed.

A battery containing molten salts as the electrolyte could comprise both sensor and energy source for the

signal. These batteries can only operate at very high temperatures when the salt becomes liquid. The heat

of a forest fire could provide the necessary temperature to activate the battery and thus activating the de-

vice.

Energy consumption and production:

RF signaling: 10 mW using VHF and 0.5-5 W using GPS. For the VHF signaling, a 1s signal eve-

ry 24h would require 10 mJ. This would require an average power generation of ~100 nW being

stored in a supercapacitor or rechargeable battery.

Sensors and microcontroller [4]:

o 60 nW during idle phase.

o Forest fire detection: 30-300 µW during a measurement cycle require 0.5-5 µW average

power generation for a sensor making a 1s readout every 1 minute.

o Environmental monitoring: 30-300 µW during a measurement cycle require 0.3-3 nW

average power generation for a sensor making 1s readout every 24h.

The required total average energy production is 0.5-5 µW for the fire detection system and 90-270 nW for

the environmental monitoring.

A commercial ceramic thermoelectric generator can produce 600 nW/mm2 from a temperature difference

of 5 °C [5]. A 3x3 mm2 thermoelectric generator would be able to supply both systems with sufficient

energy if the temperature difference used (for example between the air and the ground) is never smaller

than 5 °C.

Commercial silicon solar cells produce roughly 10-100 µW/mm2 [6]. A 1 mm2 solar cell is therefore suf-

ficient to power the device. However, there are only a limited number of sun hour per day and the light

conditions in the forest could be poor. A larger solar cell might be necessary to ensure sufficient power.

Another possibility is to combine a solar cell with a thermoelectric generator. The solar cell produces

more energy than the thermoelectric generator under ideal conditions, but the energy supply of the ther-

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moelectric generator could be more constant and reliable.

A supercapacitor with the electrode weight of 1 mg is sufficient to store the energy needed for transmis-

sion [7].


Solar power

Thermoelectric power from air/ground/water

Pyroelectric or thermoelectric power from forest fires

RF energy of an antenna is close by

Battery to store energy for sending the signal

Supercapacitor that stores energy harvested from the surrounding

System design

The system comprises:

Sensors (temperature, pH, relative humidity, etc.)

Microcontroller

RF transmitter

Energy harvesting device (solar, thermoelectric, pyroelectric)

Supercapacitor/battery

The sensors for forest fires could be IR sensors, temperature sensors, humidity sensors or carbon dioxide

sensors. The sensors for environmental monitoring could include pH sensors and humidity sensors for air,

water and soil. The system could be constructed with classical electronics, but if a large number of such

devices are needed then the cost could become an issue. By manufacturing some of the parts using printed

electronics the total cost could be minimized. Sensors, energy harvesters and supercapacitors/batteries

could potentially be printed.


The system could be produced using only classical electronics, but to minimize the cost, some parts of the

device could be manufactured using printed electronics.

Printable parts:

Sensors (temperature, pH, humidity, etc.)

Batteries and supercapacitors

Thermoelectric generators and solar cells

Research needs

For printed devices to be used in the system there is a need for improved stability and lifetime. A forest

monitoring system should have a lifetime of at least 10 years which could be a challenge for current

printed batteries, supercapacitors and energy harvesting devices.

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References:

[1] The Online Journal on Electronics and Electrical Engineering (OJEEE) Vol. (3) – No. (2)

[2] https://www.fraunhofer.de/en/press/research-news/2011/may/microclimate-forest.html

[3] https://www.cs.ox.ac.uk/files/2112/ThesisSubmitv2.pdf

[4] http://ww1.microchip.com/downloads/en/DeviceDoc/39927c.pdf

[5] JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 13, NO. 3, JUNE 2004

[6] http://www.josh.com/Solar/CellsCompared.htm

[7] http://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor

Smart homes

Background

A smart label including sensor, energy harvesting, energy storage, wireless communication for multiple

uses in a smart home. An example application is a wireless alarm sensor that sends a signal if a door or a

window is opened. Most alarms used today uses wires to connect to the sensors placed at doors and win-

dows, which leads to a large installation cost. Alarms are usually also not owned by the customer but by

the company providing the service. If the customer decides to change provider of the service the installa-

tion and wiring has to be done again. A wireless sensor system greatly facilitates installation and change

of service provider and also reduces the cost.

It is important to point out that the system is made out of different modules, enabling large variations in

the functionality by simply replacing a module. Just by exchanging the sensor type one can have an en-

tirely different application. It is also possible to change the energy harvesting source or use multiple har-

vesting devices.

Use case

A smart label will be placed on or in the vicinity of doors and windows. This gives the possibility to uti-

lize several energy sources for harvesting of energy: motion of door or window opening and closing,

movement of people, temperature gradient between indoor and outdoor environment, temperature fluctua-

tions over time (e.g. day/night), ambient light, RF energy.

Market analysis

After many years of slow adoption, the concept of the smart home has recently entered the mainstream.

The age of mobile devices, cloud connectivity, and the internet of things means that solutions for home

automation have been reinvented for the digital age.

The smart home market is forecast to grow from $3.6 billion in worldwide hardware, services, and sub-

scriptions revenues in 2012, to $14.7 billion by 2017.

The smart home market was once almost entirely reliant on the construction of new homes. However, the

growth of wireless connectivity over the last decade has changed the way home automation systems are

now installed.

Instead of building a new home with cables running throughout the building, or tearing down walls to do

install cabling in an existing one, sensor devices are now able to communicate with each other wirelessly.

This has meant that installation of smart home systems can be carried out with much less disruption,

much more easily and at a fraction of the cost than was previously possible.

https://www.fraunhofer.de/en/press/research-news/2011/may/microclimate-forest.html

https://www.cs.ox.ac.uk/files/2112/ThesisSubmitv2.pdf

http://ww1.microchip.com/downloads/en/DeviceDoc/39927c.pdf

http://www.josh.com/Solar/CellsCompared.htm

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The fastest growing part of this new smart home market is the do-it-yourself segment. This segment is

fuelled by a wave of new products that consumers purchase, install and manage themselves. Solutions

range from window contacts, to temperature, light, or humidity sensors; from presence detectors, and

CO2 metering devices, to thermal-powered heating radiator valves, or complete smart home systems.

Most residential alarm providers now offer wireless solutions for the installation of different sensors

throughout homes. Virtually all of these companies also employ a wide range of wireless trips and trig-

gers due to their low cost, ease of installation, and reliability. For these systems, reliability is a major

factor, as a system failure can often imply serious consequences. It is estimated that in today’s residential

alarm market, more malfunctions are caused by battery failures than by the electronics themselves.

Thus, one area of potential future improvement lies within the area of power supply. Replacing traditional

battery-powered energy supplies with energy-harvesting systems can improve the reliability of sensors

deployed in smart home systems.

To further illustrate the potential market for home automation, we need look no further than to some of

the companies currently powering the consumer digital revolution:

Apple has followed the home automation trend, and late in 2014 announced a new platform

called HomeKit. HomeKit will enable consumers to have full wireless and electronic control of

their homes, household features, activities, appliances, and more.

Google was somewhat quicker to see the potential within the smart home segment and ac-

quired Nest Labs for $3.2 billion in January 2014. The high price tag of the acquisition (coupled

with Google’s newcomer status to the smart home market) made headlines and confirmed the

company’s interest in home automation.

Samsung acquired a company called SmartThings in august 2014, for a reported $200 mil-

lion. SmartThings turns your smartphone into a remote to control for smart devices in your

home.

So, while the smart home has traditionally been a market for early adopters, the growth of key technolo-

gies such as mobile, cloud computing and the Internet of Things has widened the appeal of the connected

home in recent years. Momentum for the smart home is expected to increase further during 2016, as

products compatible with Apple’s HomeKit, Google’s Nest, Samsung's SmartThings, and industry-driven

efforts such as the AllSeen Alliance and Universal Plug and Play (UpnP) all compete to establish them-

selves with manufacturers and consumers alike.

As a means to facilitate maintenance of these wireless systems, and at the same time increase their relia-

bility, energy harvesting technology is an attractive option. Energy harvesting also means reduced opera-

tional costs if we can avoid the replacement of the billions of power cells potentially required to power

sensors in smart home installations.

Energy budget

A central control unit connected to power outlet should be able to activate and deactivate the smart labels

wirelessly. Provided that the alarm is active energy will be needed if a door or window is opened in a

burglary attempt. The energy required is for sensor readout, microcontroller, wireless communication (eg.

http://www.smartthings.com/product/

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bluetooth low power). A signal should be sent via bluetooth from the smart label to the central control

unit, likely located within 1-50 m of each other. To send a signal using low power bluetooth a power of

10-500 mW is typically needed, where the power level depends on the distance the signal should be sent.

To send 1 data package takes 3 ms. The power needed for a low power microcontroller to read the sensor

can be in the range of 30-450 µW (10-150 µA, 3 V) for a duration of around 1 second.

The energy needed to send a data package via low power bluetooth is estimated to 500mW*3ms=1.5mJ.

One activation of the microcontroller and sensor readout is estimated to 0.45mW*1s=0.45mJ. This gives

an energy consumption of around 2mJ.

Based on a reported device[1] the harvested power can be at least 5µW. This means that the device can be

activated roughly every 400 seconds.


There are a lot of possible choices that can be made regarding which type of energy source to be harvest-

ed. Some examples are piezoelectric harvester for motion, thermoelectric harvester for temperature gradi-

ents, pyroelectric harvester for temperature fluctuations, photovoltaic harvester for light, RF energy har-

vesting of ambient radiation. Since a smart home is likely located in an urban or semi-urban environment

the levels of ambient RF radiation can be high enough to make harvesting of this type of energy source a

good choice.

System design

A smart label system will include a sensor capable of detecting if a door or a window is opened (or bro-

ken in case of a window). This can for example be based on a contact being opened or closed, or a micro-

phone recognizing the sound of a broken window. A harvesting device can be based on harvesting of

ambient RF radiation. The harvesting part of the device will include an antenna, a matching network, an

RF-DC charge pump, and a charge storage. The charge storage will be connected to a microcontroller,

powering it during sensor read-out operations. Communication with a central control unit can be made via

low power bluetooth. The system can be made using traditional electronics, but many parts can be manu-

factured by printing: antenna, parts or all of matching network and RF-DC charge pump, charge storage

in the form of a supercapacitor.

This type of system has been reported[1], where the source was UHF digital TV band 512-566 MHz , dis-

tance to source 6.3 km. The measured peak carrier power level captured by the antenna was 0.32 µW

while the net harvested wireless power was 126.2 µW. The maximum RF-DC conversion efficiency was

5.5% and 15% respectively for 1 MΩ load and 18 MΩ load.

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Figure 28 Operation of embedded MCU powered by ambient wireless power at the UHF digital TV band in Tokyo, Japan

(channel power:-8.99 dBm = 126.2 µW): (a) power-up mode, (b) sleep/charge mode, (c) active/discharge mode, and (d)

transition from active to charge mode.


Antennas, resistors, super capacitors and conductive tracks can all be printed. Capacitors and diodes can

also be printed but care must be taken to ensure that the performance meets the requirements. Printed

inductors would likely not have the required performance, in this case a better option is to use a tradition-

al commercial inductor.

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Research needs

Further research is needed for printed capacitors, supercapacitors, diodes and inductors in order to enable

printed components with sufficient performance.

References

[1] Kim, S. et al., Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless

Sensor Platforms, Vol. 102, No. 11,pp. 1649-1666, November 2014, Proceedings of the IEEE. doi:

10.1109/JPROC.2014.2357031

Summary and conclusions

The prestudy reported here shows the potential for finding energy sources as alternatives to batteries.

Numerous energy sources are available but not all would be possible to implement in an IotT application

accomplished with printed electronics.

Three typical cases for IoT applications have been analyzed; industrial, outdoor and home environment.

In all cases it is likely that an implementation of a printed (or produced with printlike methods) could be

possible.

The present review and overview of energy sources is an important tool for further development.

The project has also meant a closer collaboration between Acreo Swedish ICT and HiQ with an identifi-

cation of common interests and possible joint future work. One example is the “smart home” sector where

HiQ is engaged in discussions with Norrköpings kommun and local property owners for development of

future technology for the home.

Slutrapport/Final report VINNOVA SIO IoT – Dnr 2014-05164

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Transcript of Slutrapport/Final report VINNOVA SIO IoT – Dnr 2014-05164