Mobile driving energy efficiency in Managing Power in off-grid homes

Ashok Jhunjhunwala, Prabhjot Kaur, Anusha Ramachandran, Sai Ram Mannar, Mrinalini Ramakrishnan, Sree Hari Nagarajan

IIT Madras

ashok@tenet.res.in

Power for Indian Homes: A dilemma

• 50 million homes not connected to grid

• About 100 million homes have load-shedding between 4 hours a day to 16 hours a day

• 50% of Indian homes can not afford power even at subsidizedrate of ₹5 per unit

– At this tariff all DISCOMS lose money

ITS Cambridge 2

$1 = ₹66

September, 2016

Power of 125W Solar Panel

In first week of December 2015• When whole of IITM had no power for 75 hours

– Even 1 MW solar plant at IITM failed to provide any power

– one home which continued to have two tube-lights+ a bulb and a fan + laptop charged / discharged fully 15 times + cell phone charging• 125W solar panel + 0.5 kWh effective battery

– Solar DC Inverterless• Full DC wiring, all Loads DC, solar and battery connected on DC

line, input grid power converted to DC • Avoided 45% losses due to three converters

– Also, DC-powered DC loads save power• LED lights, fans with BLDC motors

TVs and all electronics arepreferably powered on DC line

ITS Cambridge 3September, 2016

AC Load

DC-AC

Battery

AC-DC DC-AC

Grid

Solar DC

Fans AC fan BLDC fan

At full Speed 72W 30W

At speed 1 60W 9W

Lighting CFL Tube light LED tube

At Max. Intensity 36W 15W

At Lowest Intensity NA 4W

Smart Homes should have Solar-DC

• DC Micro-grid connecting– Solar Panel

– Battery

– DC Appliances

• Highly efficient usage of Power– Low-power from grid alone converted from AC-DC

(Designed to have minimal losses)

• 48V DC chosen due to – Safety considerations

– Lower cable losses compared to 12V/24V DC systems

• But design non-trivial– Solar MPPT voltage varies

– Battery needs independent charge voltage

– Load is at some fixed voltage

– DC-DC converters will add similar losses

ITS Cambridge 4September, 2016

AC-DC

battery

Loadgrid

Solar

48VDC

48VDC

48VDC

IITM designed Solar-DC Inverterless

5

125W to 500W 48V DC (and possibly 150W uninterrupted AC) Power with BLE prepaid recharge

125W panels• Upto 500W possible

230V AC

Special 1 kWh VRLA battery with 1600 cycles for 50% DoD• Up to 5 kWh possible

ITS Cambridge

Designed as an expandable product, still keeping losses low

Monitored using Bluetooth

September, 2016

And worked with start-ups to build Appliances

ITS Cambridge 6September, 2016 ITS Cambridge 6September, 2016

LED Bulb• 5W instead of 30W bulb

BLDC Fan• 30W instead of 72W AC fan• 9W at lowest speed Remote Control for Fan &

Tube light• ON/OFF and for dimming

Cell phone Charger/Socket• DC charger with USB port

LED Tube light• 15W - dimmable to 4W, instead of 36W

fluorescent tube

Cost: ₹20000 for 125W SP + 1 kWh Battery+ appliances

$1 = ₹66

Energy-efficient DC appliances being expanded

7

DC-powered 19/24” Colour TV• Consumes 30W along

with set-top box at 48V DC

DC Desert Cooler• Consumes 80W

instead of 180W AC cooler

Refrigerator and Stove• Still experimental

ITS Cambridge

DC Mixer• Consumes 150W,

whereas AC Mixers consume 350W

September, 2016

Deployment of Inverterless DC Solution in off-grid rural homes

ITS Cambridge 8September, 2016

Rajasthan: 4000 Homes

Jodhpur District

Jaisalmer District

Other States: 1000 Homes

ITS Cambridge 9

Deployments in deserts of Rajasthan

September, 2016

4000 scattered Homes provide excellent field conditions

• The system design was new and complex with each sub-system beingjust optimal in terms of size and costs

• The stated aim to reduce cost and size by reducing losses

• Question: Is this reduction in losses realised in practice (it did in labprototypes) in different field conditions

• Is system functioning well at these remote location?• are sub-systems behaving right?• Is solar power getting wasted?• Is battery remaining healthy?• Can performance be further improved?

– Cost / performance needs to be examined

September, 2016ITS Cambridge 10

Need to monitor each system

• For the purpose of diagnostics and performance evaluation– Measure solar-power, battery (in / out)

power and Load power every few minutes

– Building such diagnostics in Inverterless was trivial

• But requires connectivity to the cloud

• Needs to be Low-cost as compared to Inverterless– Operations costs needs to be low

• Inverterless costs ₹3000; wireless modem will cost similar + monthly cost of usage– Need a different approach

• Most homes have a phone• Use Blue-tooth to connect

– Use phone to relay to cloud

ITS Cambridge 11September, 2016

Over Internet

$1 = ₹66

Connectivity for Power Management

• Connectivity can do more, not just Monitoring

• Management

ITS Cambridge 12September, 2016

Remote Monitoring helps

• Faults example– Certain repeated short-circuit

behaviour

• Design deficiency examples– Battery may be charging / discharging

faster• Solar pattern variance

• Usage pattern variance

• Blackout period pattern, if grid-connected

– Battery switching from normal to boost

– End of Life (for battery behaviour

• Some can be corrected by software/ algorithm upgrades– Some other would require hardware

changes

• A major design aspect that emerged– Provision of an emergency line kept

ON when SoC of battery goes low

ITS Cambridge 13September, 2016

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Measurements from a home in Bhom Ji ka Gaon, Jodhpur from 9am to 5pm

• Understanding use of solar Power and losses: performance evaluation• Is customer using more than what solar power provides?

• Is she using less? Is power being wasted?• In Grid-connected system (no reverse feeding for small system), grid-usage can be optimized

to use all of solar power

Solar

Battery

Load

ITS Cambridge

-75

-55

-35

-15

5

25

45

65

85

105

125

Jul-

01

00:

00

1:5

5

3:5

0

5:4

5

7:4

0

9:3

5

11:3

0

13:2

5

15:2

0

17:1

5

19:1

0

21:0

5

23:0

0

Jul-

02

00:

55

2:5

0

4:4

5

6:4

0

8:3

5

10:3

0

12:2

5

14:2

0

16:1

5

18:1

0

20:0

5

22:0

0

23:5

5

Day and Time

Battery power (W) Load power (W) Solar power (W)

September, 2016

Remote Monitoring monitors Usage

ITS Cambridge 15

Solar Power not fully Captured, as load is less and Battery is full

September, 2016

Lower Usage may waste Solar Power

Customer Monitoring

• Using Mobile App on customer phone

– Tracks power usage throughout day

– Tracks power generated and stored

– Tracks State of Charge (SoC) of battery

• For grid connected system

– Power availability

– Help her plan conserve if required• Dim lights / fans

– Helps user alter usage to avoid waste

ITS Cambridge 16September, 2016

Management using connectivity

• Manage at what SoC battery should switch to emergency load andto cut-off– Depends on solar power availability at a location and load usage patterns

• Manage (using user mobile or from cloud) order of priority inutilising solar power, grid power and battery to drive load– makes the Inverterless system highly adaptable

• Configuring parameters like voltage thresholds and power-availability for battery to go in Boost Charging mode

September, 2016ITS Cambridge 17

Management using connectivity

• Four home cluster system allows homes to share the fixed costs, includingsolar panels and battery pack

– Homes unlikely to use peak load simultaneously: enables system design for averageloads

– mobile application helps monitor usage patterns, implement usage limits and billing forindividual homes

• ‘Pay as you go’ models for Inverterless administered using Bluetoothapplication

– packages can be designed for users to purchase credit for power only when they require

– can discontinue and resume usage

September, 2016ITS Cambridge 18

Learnings from monitored deployment

• When will Micro-grid help? Can wastage of Solar Power be avoided

• How will use of Li-Ion battery and reduction of losses to 5% help and at what cost-point?

• Capital and Operation Costs of grid Vs off-grid solar

• How much will on-grid Inverterless help?

ITS CambridgeSeptember, 2016

Ashok Jhunjhunwala, Aditya Lolla, Prabhjot Kaur, “Solar-DC Microgrid for Indian Homes: Transforming Power

Scenario”, IEEE Electrification Magazine, Vol 4, Issue 2, pp: 10-19. June 2016

Jhunjhunwala, Current Science, Vol. 111, No 4, August 2016 http://www.currentscience.ac.in/Volumes/111/04/0599.pdf

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Small Home AC Home DC Home

Energy/ day kWh

Cost per day ₹

Energy / day kWh

Cost per day ₹

AC Grid + 0 LS 3.27 16.3 1.29 6.45off-grid + Battery + Solar 4.9 50.6 1.33 12.6AC +Battery + Solar + 4h LS 3.75 28.9 1.35 7.3

And finally the economics

Device Numbersdeployed

Operationhrs/ day

Tubelights 2 6

Fans 2 12

Bulbs 2 10

Phones 1 4

TV 1 10

Cost / day includes depreciation and interest for solar panel and battery assuming grid costs of ₹5 per unit

ITS Cambridge 20

Off-grid home power-costs with solar-DC (₹12.6 per day) less than the cost of on-grid AC homes with no power-cuts (₹16.3 per day) $1 = ₹66

September, 2016

To Sum Up

• 500W solar power (50 sq ft) with DC appliances can take care ofmost essential loads in middle class homes– 240M homes with 500W solar panel produces close to total domestic

consumption in India in a year• 240M x 0.5 kW x 1550 solar hours a year = 190,000 GWh per year

• Innovative systems like solar-DC needed to provide power to lower sections of people in India

• Monitoring and Managing Power for such small systems is a true example of power of IoT

September, 2016ITS Cambridge 21