PAN-IIT Solar Thermal Project-Experiences at IIT Madras

Coordinators:

T Sundararajan (IIT M)

K. Srinivasa Reddy (IIT M)

R.P. Saini (IIT R)M. V. Rane (IITB)

P. Muthukumar (IITG)

Background for Project

• The Govt of India has announced Solar Energy asone of the thrust areas for the 11th and 12th fiveyear plans

• In order to rope in premier academic institutionsfor solar energy research, a PAN-IIT solar energyproject was conceived and the IITs were invitedto submit a combined proposal

• The objective was to set up 1 MWe solar powerplant in collaboration with industry and also toaddress research challenges in solar powergeneration

Grand PAN-IIT Proposal on Solar Power

• It was intended to address research issues of SolarPV, Solar Thermal, Energy Storage and ElectricalInterfacing and Control.

• About 30 faculty members from different IITsparticipated and a Grand Proposal requesting asupport of 30 million USD was submitted to theDepartment of Science & Technology, GOI

• An expert committee set up for evaluation adviseddivision into separate Solar PV and Solar Thermalproposals with electrical interfacing being common

Grand Proposal

Grand Proposal – Solar PV

Grand Proposal – Solar Thermal

PAN-IIT Solar Thermal Project

• The three sub-themes of the Solar Thermalproject are : (i) Direct Steam Generation basedSolar Power Plant (ii) Storage of ThermalEnergy for Solar Power Plant (iii) SolarRefrigeration based on liquid dessicants

• The power plant is rated at about 500 kWthand a storage capacity of 3 GJ energy. Thesolar refrigeration planned is for a capacity of30 tons.

DIRECT STEAM GENERATION BASED SOLAR POWER PLANT

Solar Thermal Power Generation

• An intermediate thermic fluid has often beenused as heat transfer medium and also as apartial storage system.

• Use of thermic fluid allows the solar collector tooperate near atmospheric pressure

• However, decomposition of fluid over time, lowertemperature levels, heat losses in theintermediate heat exchanger and extra cost haveled to direct steam generation based systems

10

Solar Parabolic Trough Thermal Power Plant – Thermic Fluid

Direct Steam Generation by Solar Parabolic Trough Collector at

IIT Madras

Research Plan of PAN-IIT Thermal Project

• Carry out basic studies on simulated solarcollectors, two phase flow instabilities,various thermal storage systems and liquiddessicant based air conditioners at IITs

• Develop a pilot scale system with powerpack (500 kWth) in collaboration withPathashaala, a school in rural district ofTamil Nadu.

• Develop component and system levelmodels and validate them with experimentaldata

Research Issues

• Solar energy concentration with effective use ofland area

• Reduction of heat losses from the receiver

• Optimisation of receiver configuration

• Investigation on effects of selective coatings

• Study of single and two phase flow heat transfer inthe water tubes

• Accurate flow and heat transfer model atcomponents & system level

• Utilisation of waste heat for Solar A/C

• Efficacy of various materials for latent heat andsensible heat storage

Overall System Configuration• Solar Concentrator with Linear Fresnel mirrors (due

to manufacturing ease, compactness, low wind

load) and supported by secondary concentrators

and 1-axis tracking system

• Receiver cavity with water absorber tubes and

selective coatings; Evacuated tube type receivers in

high temperature section

• Segmented heating and two-phase storage at high

pressure and temperature (~65 bar, 400 deg.

Celsius)

• Power generation & heating applications using highpressure, high temperature steam

Concentrated Solar Collector with Evacuated Cavity Receiver

Coated absorber tubes

Cavity insulation

Antireflection Coated glass cover Cavity receiverwith water tubes

Concentrating mirrors

Estimates for 500 kWth system

• Consider about 1500 square meters of mirrorarea.

• Incident solar energy ~0.8 kW x 1500 = 1200 kW

• Absorbed fraction (~ 50%) = 600 kW (thermal),with a little excess capacity

• Conversion to electricity (~20%) = 120 kW

• With enthalpy change of about 3000 kJ/kg, waterflow rate = 600 kW/ (3000 kJ/kg) = 0.2 kg/s

• Required land area~ about 4000 sq.m (one acre)

Production of High Temperature Steam

• It is aimed to produce steam at 65-50 bar pressure and temperature of about 400oC

• At high temperature, heat losses need to be reduced. Coatings with high optical absorptivity and low thermal emissivity will be needed for absorber tubes

• Heat flux on the absorber tube needs to be spread out to avoid hot spots

• When vapor fraction increases, internal surfaces may be needed to compensate for low heat transfer coefficient

Modelling Aspects• A specular reflection based radiation model will be developed

to investigate the solar concentration by Fresnel mirrors. Theheat flux distribution on receiver cavity will be estimated usingthis model.

• A multi-mode heat transfer model will be developed to studythe natural convective air flow and heat losses from thereceiver cavity. This model will be used to optimise thereceiver cavity geometry and investigate the effects of vacuumlevel and selective coatings.

• A two-phase flow model will be developed for the water tubes,to study the flow instabilities and heat transfer effectiveness.

• These component level models will be validated usingextensive experimental data collected in the lab scale and pilotscale models.

System Level Models

• Apart from the component level models, asystem level transient model will also bedeveloped including two- phase storage. Thismodel will be used to study the transientbehaviour of the collector system over a dayand from season to season.

• The system level model will be validated usingexperimental data obtained at the pilot plant

Pilot Plant Studies at Pathashala

• A Pilot Solar Thermal Power Plant of about 500kWth capacity will be set up

• The facility will be fully instrumented to obtaindetailed measurements on the variations ofpressure, temperature and steam quality atdifferent locations; also, factors such as dailyaverage solar insolation, wind speed and humiditywill be monitored.

• It is also aimed to provide electrical power andsteam for cooking/washing for the studentcommunity residing at this school from the plant

SOLAR THERMAL ENERGY STORAGE

Thermal Energy Storage

• Energy could be stored thermally as latent heat or as sensible heat. Of course, there are other chemical and electrical storage methods as well.

• Latent heat storage at high temperature levels could be achieved through the use of molten salts. For power plant usage, steam accumulators themselves could be considered as useful options to provide steam readily on demand.

• Sensible storage of heat could be done by heating any block of large heat capacity

Molten salt storage system

Parabolic Trough Collectors with

two tank storage system

One tank Thermocline storage

system

Steam Accumulator based storage

system

Storage with Steam Accumulator

and Sensible Storage

Research & Development on Thermal Storage

• Thermal storage in steam accumulators at 80bar and 300- 350oC, for a capacity of 2.5 GJ

• Sensible energy storage in blocks of cast steel,fire bricks and concrete blocks up to 400oC, fora capacity of 0.25 GJ (The mass of blocks isestimated to be about 4000 kg).

• Combinations of phase change materials willbe used to store another 0.25 GJ of heat attemperatures up to about 600oC.

Properties of Salts to be used as PCMs

• The salts under consideration are: MgCl2 /KCl/NaCl (380oC, 400 kJ/kg) and KOH (360oC,134kJ/kg), KNO3(335oC,95 kJ/kg), KNO3/KCl (320oC,74kJ/kg) and NaNO3 (335oC,95 kJ/kg) where themelting temperature and the latent heat of thesalt are indicated in brackets. These are to beused in cascade storage systems.

• In addition to these other PCMs which could beemployed are AlSi12 (576oC, 560 kJ/kg) and AlSi20

(585oC, 460 kJ/kg).

Cascade Storage System

SOLAR THERMAL AIR CONDITIONING

Objectives

• Here, it is aimed to provide conditioned air to theinstrumentation & control room for operating thepilot plant and also for human comfort, wherepossible

• Primarily, the A/C system will be a waste heatrecovery unit which taps low grade energy (~60oC)and utilizes it to produce useful refrigeration effect

• This is achieved by dehumidifying air with the helpof liquid dessicant and regenerating the dessicantwith low grade energy. The air temperature andhumidity could be controlled by evaporative cooling

Solar Air Conditioning

• A stand alone hybrid air conditioner operated by solar PV andLiquid Dessicant based system is planned for maintaining thecontrol room and office space at 25 oC and 50% RH.

• Regeneration of the liquid dessicant is achieved using the heatrejected in condenser. Expected COP of the hybrid AC system isbetween 3.9 to 4.5.

• Another bleed steam driven liquid dessicant based system isplanned for maintaining 27 oC , 60 RH in the battery and inverterrooms. Here, the fresh air will be dehumidified, evaporativelycooled and further dehumidified to obtain the desired conditions.Bleed steam will also be used for dessicant regeneration.

• Modular 2 TR hybrid and 3 TR liquid dessicant based ACs areplanned for a total capacity of 30 TRs.

Summary

• Three major projects are under way withfunding to the tune of 3 million USD from theIndian Government on the development ofdirect steam generation solar power plant,solar thermal storage and solar refrigeration

• The projects are expected to address some ofthe research challenges on solar energy basedgreen solutions for power generation

Development of Solar Collector Field for Solar Thermal

Power Plant

(Phase I: Nov. 2012 to May 2014)

Principal Investigators:

Prof. T. Sundararajan and Prof. K. Srinivasa Reddy

Department of Mechanical Engineering, IIT Madras

Objectives

In Phase I, it is desired to:

• design and develop fully instrumented lab-scaletest facilities for studying solar receivers andabsorbers for high pressure and temperature.

• design and develop a storage-integrated solarcollector field of 50 kWth capacity with variablesteam output (50 bar pressure and 350-400°Ctemperature) at The Pathashala campus,Vallipuram, Kanchipuram district.

• develop a heat transfer model for analyzing andoptimizing the solar collector field.

Methodology

• A collector field involving Linear Fresnel Reflectors(LFR) has been designed to concentrate solar energy onto a coated absorber tube made of stainless steel.

• The absorber tube is enclosed inside another boro-silicate glass tube, with the annular space beingevacuated to reduce heat losses.

• In a steam-separator cum storage device, the saturatedsteam will be separated and sent for super-heating.

• The higher temperature range of 400oC (at about 50bar pressure) will be achieved with the help ofsecondary concentrators, for increasing theconcentration ratio.

• A solar collector field for a capacity more than 50 kWthhas been designed and it is being fabricated at present.

Tasks completed so far• Design of 50 kWth solar collector field for direct steam

production at 50 bar, 400oC• Provision of an access road to the Pathashala project site• Soil testing and leveling at project site• Design of distilled water set-up involving pump installation,

piping from the water source (well) to the water tank anderection of a shed for water utility equipment and on-siteconstruction

• Design and construction of mount structures for LFR mirrorsincluding single axis tracking system at KG Design Services

• Ordering of LFR mirrors and coated stainless steel absorbertubes with evacuated glass casing, as required by the solarcollector field from foreign suppliers

• Placement of purchase order with M/s KGDS Coimbatore forthe fabrication and installation of the storage integrated solarcollector field

Schematic view of the proposed systemReceiver

Reflectors

Steam separator

RO – DM plant

Mixing tank

Water from Bore well

Raw water tankOutlet superheated

Steam at 400 C and 50 bar

Inlet water from DM tank

A-frame

Feed pump

Solar Collector Field LayoutTotal Land area required 466 m2

Total solar field collector area 308 m2

Effective land usage 66 %

Saturated section 154 m2

Super heater section 154 m2 (Minimum area)

Super heater Section Evaporator Section

Steam Separator

1.07 m

0.43 m

6 m

12 m Feed water to inlet

Steam Outlet 17.57 m

N

Mixing drum

Feed water

in

Solar Reflector and Receiver specifications

Reflectivity of the primary reflector 93.0%

Reflectivity of secondary reflector 90.0%

Transmittance of AR coated borosilicate

glass in the evacuated solar collector tube96.5%

Absorptance of the receiver tube 95.0%

Emissivity at 400 oC 7.5%

Overall ratio of thermal energy collected to

solar radiation62%

Meteorological data : Vallipuram (12.65° N, 79.74° E)

Jan Feb Mar AprMa

yJun Jul Aug Sep Oct Nov Dec

Ann.

Aver.

DNI

(kWh/m2/

day)

5.44 6.35 6.80 5.96 5.37 4.26 3.52 3.61 4.19 3.56 3.59 4.35 4.74

Precipitation

(mm/day)0.67 0.48 0.39 1.36 2.68 3.67 4.04 4.33 4.99 6.45 6.09 2.95 3.18

Wind Speed

(m/s)2.83 2.88 3.27 3.63 3.95 4.28 3.90 3.80 2.91 2.43 2.65 2.92 3.28

Wind dir. in

deg. from

true north

63 75 88 100 110 129 160 196 212 218 222 89

Meteorological Data for Pathashala Campus

Determination of solar insolation and collector thermal efficiency

Patashala

Vallipuram

Proposed

Solar field

area

N

Proposed location of solar field area

General layout of V50 Phase-I

Pathway for providing access to the project site

Shed for water utility plant & site construction

Well for water supply to process

Receiver

Linear Cavity Receiver

• Light and sturdy

• Ease of fabrication

• Simple methods of mounting secondary reflector and absorber tube

• Thermal expansion provision for Secondary receiver and absorber tubes

Secondary Reflector (SR) material

Options…

• Almeco solar Vega HT and TS - Aluminum reflector with > 91% reflectivity

- Operating temperature – 250 C to 300 C

• Guardian Ecoguard - Concave low iron glass + silver back coated

with > 93% reflectivity

- Operating temperature – 200 to 300 C

• Alanod solar MiroSun Weather Proof 90 - Aluminum reflector with > 91% reflectivity

- Operating temperature – 200 to 300 C

Almeco Solar

Secondary Reflector

profile testing

Secondary Reflector

70 mm Dia Absorber

tube

Design of Secondary Concentrator based on Ray-tracing technique

70 mm Tube

Secondary reflector

Laser beam falling and reflecting from the secondary concentrator

Successful secondary reflection on to the absorber tube.

0 deg incidence @ 10 mm from edge

0 deg incidence @ 110 mm from edge

15 deg incidence @ 110 mm from edge

15 deg incidence @ 160 mm from edge

30 deg incidence @ 210 mm from edge

30 deg incidence @ 410 mm from edge

Evacuated absorber tube

Evacuated solar collector tube – Archimede Solar

Tube material :Material : SS 304 seamless tubes OD: 70 mm; Thickness: 4 mm; Length: 4 m

Outer cover :125 mm diameter double side AR coated toughened

borosilicate glassSolar selective coating : Sputtered cermet coatingAbsorptivity : 95%Emissivity : 7.4%Maximum Operating Temperature and pressure

: 580 deg C ,55 bar

Durability :As per the warranty proposed by the manufacturer.(> 10 years)

Sputtered cermet coated absorber tube with

low emittance

Evacuated toughened borosilicate glass jacket

Evacuated solar collector tube – TRX solar, China

Tube Specification:

Operating temperature is 450 C and pressure at 55 bar

Length: 4060mm

Absorptance: 96% (AM=1.5)

Emissivity: ≤10% (at temperature 400°C)

Absorber tube Outer diameter: 70mm

Thickness: 3 mm

Steel type: SS 304/321

Glass Outer diameter: 125mm

Glass Thickness: 3mm

Transparence with anti-reflective coating of ≥96%

Without anti-reflective coating of ≥91.5%

Prototype

Receiver when all the mirrors are focusing onto the receiver

Radius of Curvature testing and study… 8 Structures…

Mirror clamps… for study

Mirror support with one-axis Sun-tracking

Work to be completed

• Apart from solar collector studies at the Pathashala site,laboratory scale research set-ups will be fabricated andtested at IIT Madras for evaluating the two-phase flowinstabilities and the thermal properties of variousinsulation, piping, coating and other materials.

• Also, the solar insolation and environmental conditionsat Pathashala will be studied in detail, with the help ofsolar power meters and a weather monitoring system.

• These studies will be carried out by setting up a collectorfield of 50 kWth capacity and carefully evaluating itsperformance characteristics.

Work planned in Phase II

• In Phase II, it is planned to extend the capacityof the Solar Collector system to 500 kWth.

• The steam generated by the solar collectorsystem will be connected to a steam turbinewhich will be purchased off-the shelf.

• The power pack and control instrumentationwill be incorporated

Thank you