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Advancement of Solar Thermal Technologies

Jane H. DavidsonDepartment of Mechanical Engineering

University of Minnesota

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Renewable energy potential is many times the world demand for energy

NG 23%

Nuclear 8%

Petroleum 40% Coal 23%

Biomass 47%

Wind 2%

Hydroelectric 45%

Geothermal 5%

Solar <1%Renewables

6% Diffuse and intermittent

~1000 W/m2

Capture/convert/store/ transport Initial cost Rapid scale-up &

deploymentSource: Renewable Energy Trends 2004; Energy Information Administration, August 2005.Note: Total U.S. Energy Supply is 100.278 QBtu; Energy Information Administration, August 2005.

Challenges

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SOLAR ENERGY OPTIONS Utility Scale Concentrating solar

thermal power Solar fuels Photovoltaics Wind Biomass

Distributed Heating/cooling Hot water Photovoltaics

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State of the Art: Distributed Low Temperature Solar Technology

Hot water, space conditioning, agriculture, industrial process heat, ventilation air

Temperatures < 100 °C Proven and reliable for hot water

− Rated and certified by SRCC− Annual efficiency = 40%

Immediately deployable 1% market penetration for H2O

Use & Status

Conventional flat plate collector

Ventilation for space heating

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The Potential Benefitsfor US Buildings

Transportation27%

Commercial 16%

Residential 20%Industrial

37%

65% of total U.S. electricity consumption 36% of total U.S. primary energy use 30% of total U.S. greenhouse gas emissions

Buildings

Source: Energy Consumption US DOE Annual Energy Outlook

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Distributed Low-temperature Solar Thermal

Barriers Initial Cost Storage capacity for space conditioning Building integration

Current Research Focus A paradigm shift from copper and glass components to mass manufacture with polymers High strength, high thermal conductivity polymeric

materials for absorbers and heat exchangers Glazing and heat exchange materials that resist degradation due to UV radiation, water and oxygen, and mechanical and thermal stresses Fundamental research on particle-surface interaction

and precipitation/deposition process Development and characterization of compact storage

media

50 µm

CaCO3 on PPWang, Y., Davidson, J.H., and Francis, L., J. of Solar Energy Engineering, 127, 1, 3-14, 2005.

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Concentrated Solar Thermal

100 SunsLine focus; limited to 750K

1000 Suns2-axis tracking; 1000K

10,000 Sunson-axis tracking; 2500K

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State of the Art: Solar Thermal Electricity

(Concentrating Solar Power)

11 MW-e/ 55 MW-th (Sevilla, Spain) 624 heliostats; each 120 m2 Tower height: 100 m Rankine-cycle Converstion = 21% peak and 16% avg. Cost (incl. power block): 35 M€

Potentially lowest-cost utility scale solar electricity for the Southwest

4.56 GW installed or planned in US, Mexico, Europe, Middle East, Asia and Africa

Annual Performance̶ Solar to electric conversion 12 to 25%̶ Capacity factor 30 to 75%

Current Cost - 12 to 14 ¢/kWh̶ 2011 - 8 to 10 ¢/kWh̶ 2020 - 3.5 to 6 ¢/kWh

Use & Status

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Barriers and Research Needs Materials̶ Selective surfaces for external receivers in towers and

dishes̶ Optical materials that are cheaper than glass but still

provide long life operation̶ Engineered surfaces that prevent dust deposition̶ High-temperature materials for tower and dish receivers̶ Thin film protection layers for reflectors

Thermal storage for CSP Working fluids with greater operating temperature range More efficient receivers

Solar Thermal Electricity (Concentrating Solar Power)

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Evolving: Thermochemical Production of Fuels

Prototype and laboratory scale̶ Material synthesis & processing̶ Hydrogen production̶ Gasification̶ Reformation̶ Recycle of hazardous wastes

Use & Status

Solar Fuels

Absorption Heat

QH,TH

ChemicalReactor

FuelCell

W

QL,TL

ConcentratedSolar Radiation

Reactants

“The fact that sunlight reaching the earth is essentially at a temperature of 5800 K thus gives it obvious advantages as a source of process heat for the production of chemical fuels. It is up to us to exercise our ingenuity to invent a mechanism by which it can be done.”

E. A. Fletcher, Science 197, pp. 1050-1056, 1977

Upgraded fossil fuels

Converts solar radiation to chemical potential

Provides long-term storage Cost competitive if carbon emissions

are considered

DecarbonizationH2O-splitting

Solar Hydrogen

ConcentratedSolar Energy

Fossil Fuels(NG, oil, coal)

Optional CO2/C Sequestration

H2O

SolarGasification

SolarReforming

SolarThermolysis

SolarThermochemical

Cycle

Solar Electricity

+Electrolysis

Graphics courtesy of Prof. Aldo Steinfeld, ETH-Zurich

∆H°

∆G°

T∆S°

-50

0

50

100

150

200

250

300

1000 2000 3000 4000 5000

[kJ/

mol

]

Temperature [K]

H2OHOH2

OHO2

00.10.2

0.30.40.50.60.70.80.9

1

2000 2500 3000 3500 4000

Temperature [K]

Equilibrium Mole Fractionp = 1 bar

2 2 2H O H + ½ O→

Solar Thermolysis

Direct thermolysis is not practical: Requires extremely high temperatures for reasonable dissociationA most critical problem is the need to separate H2 and O2 at high temperatures.

Two-Step Water Splitting Cycle

H2H2O

½ O2

HYDROLYSERZn + H2O = ZnO + H2

∆H = -62 kJ/molTL = 700 K

SOLAR REACTOR ZnO = Zn + ½ O2

∆H = 557 kJ/mol TH > 2000 K

ZnO Zn

ZnO recycle

0

0.8

1

Temperature [K]0 1000 2000 3000 4000

Carnotabsorption η⋅η

Carnot

10005,000

10,0000.2

0.4

0.620,000

1) High specific surface area augments the reaction kinetics, heat transfer, and mass transfer

2) Large surface to volume ratio favors complete or nearly complete oxidation3) Entrainment in a gas flow allows for continuous and controllable feeding of

reactants and removal of products4) Proof of concept with 95% conversion5) Next steps: to understand the kinetics of the combined formation and hydrolysis

reaction particularly the particle interactions that are concurrent with chemical reaction

Benefits

Formation of zinc nanoparticles followed by in-situ hydrolysis for hydrogen generation.

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Barriers and Research Needs Solar Step̶ Radiative transport coupled to reaction kinetics of

heterogeneous chemical systems̶ Radiative exchange with particle suspensions in a

variety of applications̶ High temperature materials and coatings

Hydrogen Production Step• Particle size resolved kinetics of hydrolysis of single

particles • Coupled Processes in particle/steam flow

Solar Thermochemical Fuels

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• Recommendations

1. Support research on a variety of solar technologies

1. For more mature technologies such as low temperature solar thermal and concentrating solar power focus on cost reduction strategies

1. Invest in basic research on solar thermochemical production of fuels

Decarbonization of fossil fuels and carbothermal reduction processesThermochemical water splitting cycles with no carbon emission

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• References– Low temperature distributed solar thermal1. Davidson, J.H., Mantell, S.C., and Jorgensen, G., “Status of the Development of Polymeric Solar Water Heating

Systems,” in Advances in Solar Energy, D.Y. Goswami, ed., American Solar Energy Society, Vol. 15, pp. 149-186, 2002.

2. Davidson, J.H., Mantell, S.C., and Francis, L.F., “Thermal and Material Characterization of Immersed Heat Exchangers for Solar Domestic Hot Water”, in Advances in Solar Energy, D.Y. Goswami, ed., American Solar Energy Society, Vol. 17, pp. 99-129, 2007.

3. Davidson, J. H., “Low-Temperature Solar Thermal Systems: An Untapped Energy Resource in the United States,” ASME J. of Solar Energy Engineering, 127, 3, 305-306, 2005.

4. Wang, Y., Davidson, J.H., and Francis, L., “Scaling in Polymer Tubes and Interpretation for Their Use in Solar Water Heating Systems,” ASME J. of Solar Energy Engineering, 127, 1, 3-14, 2005.

– Concentrating solar power1. Mancini, T., P. Heller, B. Butler, B. Osborn, S. Wolfgang, G. Vernon, R. Buck, R. Diver, C. Andraka and J., Moreno,

2003, “Dish Stirling Systems: An Overview of Development and Status,” J. Solar Energy Engineering, Vol. 125, pp, 135-151.

2. Pitz-Paal, P., J. Dersch, B. Milow, F. Tellez, A. Ferriere, U. Langnikel, A. Steinfeld, J. Karni, E. Zarza, and O. Popel, 2005, “Development Steps for Concentrating Solar Power Technologies with Maximum Impact on Cost Reduction,” Proceedings of the 2005 International Solar Energy Conference, August 6-11, Orlando, FL.

3. Sargent &Lundy Consulting Group, 2003, “Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance Forecasts,” SL-5641, prepared for the U.S. Department of Energy and the National Renewable Energy Laboratory, Chicago, IL.

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• References– Solar thermochemical processes1. E.A. Fletcher, and R.L. Moen, 1977, “Hydrogen and Oxygen from Water, “ Science, Vol. 197, pp. 1050-1056.1. Nakamura, T., 1977, “Hydrogen Production from Water Utilizing Solar Heat at High Temperatures,” Solar Energy,

19(5), pp. 467-475.2. Steinfeld, A., Kuhn, P., Reller, A., Palumbo, R., Murry, J., Tamaura, Y., 1998, “Solar-processed metals as Clean

Energy Carriers and Water Splitters,” Int. J. Hydrogen Energy, 23, pp. 767-774.3. Fletcher, E.A. Solarthermal Processing: A review. J. of Solar Energy Engineering 2001; 123:63-74.4. Perkins, C., Weimer, A. W., 2004, “Likely Near-term Solar-thermal Water Splitting Technologies,” Int. J. Hydrogen

Energy, 29, pp. 1587-1599.5. Steinfeld, A., 2005, “Solar Thermochemical Production of Hydrogen—a Review,” Solar Energy, 78, pp.:603-615.6. Weiss, R.J., Ly, H.C., Wegner, K., Pratsinis, S.E., and Steinfeld, A., 2005, “H2 Production by Zn Hydrolysis in A

Hot-Wall Aerosol Reactor,” AIChE J., 51, pp. 1966 -1970.7. Wegner, A., K., Ly, H.C., Weiss, R.J., Pratsinis, S.E., and Steinfeld, A., 2006, “In Situ Formation and Hydrolysis of

Zn Nanoparticles for H2 Production by the 2-Step ZnO/Zn Water-Splitting Thermochemical Cycle,” Int. J. Hydrogen Energy, 31 pp. 55–61

8. Ernst, F.O., Tricoli, A., Pratsinis, S.E., and Steinfeld, A., 2006, “Co-Synthesis of H2 and ZnO by In-Situ Zn Aerosol Formation and Hydrolysis,” AIChE J., 52(9), pp. 3297-3303.

9. Harvey, W.S., Davidson, J.H., and Fletcher, E.A., “Thermolysis of Hydrogen Sulfide in the Range 1300 to 1600 K,” Industrial and Engineering Chemistry Research, 37, 6, 2323-2332. 1998.