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