Advancement of Solar Thermal Technologies. Jane H. Davidson Department of Mechanical Engineering University of Minnesota

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1 Advancement of Solar Thermal Technologies Jane H. Davidson Department of Mechanical Engineering University of Minnesota 1

2 Renewable energy potential is many times the world demand for energy Renewables 6% Solar <1% Challenges Diffuse and intermittent ~1000 W/m2 Capture/convert/store/ transport Initial cost Rapid scale-up & deployment Geothermal 5% Nuclear 8% Petroleum 40% NG 23% Coal 23% Biomass 47% Wind 2% Hydroelectric 45% Source: Renewable Energy Trends 2004; Energy Information Administration, August Note: Total U.S. Energy Supply is QBtu; Energy Information Administration, August 2005.

3 SOLAR ENERGY OPTIONS Utility Scale Concentrating solar thermal power Solar fuels Photovoltaics Wind Biomass Distributed Heating/cooling Hot water Photovoltaics 3

4 State of the Art: Distributed Low Temperature Solar Technology Use & Status Conventional flat plate collector Ventilation for space heating 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 4

5 The Potential Benefits for US Buildings Industrial 37% Residential 20% Commercial 16% Transportation 27% Buildings 65% of total U.S. electricity consumption 36% of total U.S. primary energy use 30% of total U.S. greenhouse gas emissions Source: Energy Consumption US DOE Annual Energy Outlook 5

6 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 PP Wang, Y., Davidson, J.H., and Francis, L., J. of Solar Energy Engineering, 127, 1, 3-14,

7 Concentrated Solar Thermal 100 Suns Line focus; limited to 750K 1000 Suns 10,000 Suns 2-axis tracking; 1000K on-axis tracking; 2500K 7

8 State of the Art: Solar Thermal Electricity (Concentrating Solar Power) Use & Status 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 Performance 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 Solar to electric conversion 12 to 25% Capacity factor 30 to 75% Current Cost - 12 to 14 /kwh to 10 /kwh to 6 /kwh 8

9 Solar Thermal Electricity (Concentrating Solar Power) Barriers and Research Needs Materials Selective surfaces for external receivers in towers and dishes Optical materials that are cheaper than glass but still provide long life operation Engineered surfaces that prevent dust deposition High-temperature materials for tower and dish receivers Thin film protection layers for reflectors Thermal storage for CSP Working fluids with greater operating temperature range More efficient receivers 9

10 Evolving: Thermochemical Production of Fuels Use & Status Concentrated Solar Radiation Prototype and laboratory scale Material synthesis & processing Hydrogen production Gasification Upgraded fossil fuels Reformation Recycle of hazardous wastes Absorption Heat QH,TH Reactants Chemical Reactor Solar Fuels W Fuel Cell QL,TL Converts solar radiation to chemical potential Provides long-term storage Cost competitive if carbon emissions are considered 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. 10

11 H2O-splitting Concentrated Solar Energy Decarbonization H2O Solar Thermolysis Fossil Fuels (NG, oil, coal) Solar Thermochemical Cycle Solar Electricity + Electrolysis Solar Reforming Solar Gasification Optional CO2/C Sequestration Solar Hydrogen Graphics courtesy of Prof. Aldo Steinfeld, ETH-Zurich

12 Solar Thermolysis H2O Equilibrium Mole Fraction p = 1 bar [kj/mol] H2 + ½ O2 H G T S H2O H O H2 OH O Temperature [K] Temperature [K] Direct thermolysis is not practical: Requires extremely high temperatures for reasonable dissociation A most critical problem is the need to separate H2 and O2 at high temperatures.

13 Two-Step Water Splitting Cycle η absorption η Carnot 1 Carnot , , , Temperature [K] 4000 ZnO SOLAR REACTOR ZnO = Zn + ½ O2 H = 557 kj/mol ½ O2 Zn TH > 2000 K HYDROLYSER H2O Zn + H2O = ZnO + H2 H = -62 kj/mol recycle ZnO TL = 700 K H2

14 Formation of zinc nanoparticles followed by in-situ hydrolysis for hydrogen generation. Benefits 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 oxidation 3) Entrainment in a gas flow allows for continuous and controllable feeding of reactants and removal of products 4) Proof of concept with 95% conversion 5) Next steps: to understand the kinetics of the combined formation and hydrolysis reaction particularly the particle interactions that are concurrent with chemical reaction

15 Solar Thermochemical Fuels Barriers and Research Needs Solar Step Radiative transport coupled to reaction kinetics of heterogeneous chemical systems Radiative exchange with particle suspensions in a variety of applications High temperature materials and coatings Hydrogen Production Step Particle size resolved kinetics of hydrolysis of single particles Coupled Processes in particle/steam flow 15

16 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 processes Thermochemical water splitting cycles with no carbon emission 16

17 References Low temperature distributed solar thermal 1. 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 , 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 , Davidson, J. H., Low-Temperature Solar Thermal Systems: An Untapped Energy Resource in the United States, ASME J. of Solar Energy Engineering, 127, 3, , 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, Concentrating solar power 1. 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, 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. 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

18 References Solar thermochemical processes E.A. Fletcher, and R.L. Moen, 1977, Hydrogen and Oxygen from Water, Science, Vol. 197, pp Nakamura, T., 1977, Hydrogen Production from Water Utilizing Solar Heat at High Temperatures, Solar Energy, 19(5), pp 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 Fletcher, E.A. Solarthermal Processing: A review. J. of Solar Energy Engineering 2001; 123: Perkins, C., Weimer, A. W., 2004, Likely Near-term Solar-thermal Water Splitting Technologies, Int. J. Hydrogen Energy, 29, pp Steinfeld, A., 2005, Solar Thermochemical Production of Hydrogen a Review, Solar Energy, 78, pp.: 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 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 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 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,