Concentrating Solar Power
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Concentrating Solar Power The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Weinstein, Lee A. et al. “Concentrating Solar Power.” Chemical Reviews 115.23 (2015): 12797–12838. As Published http://dx.doi.org/10.1021/acs.chemrev.5b00397 Publisher American Chemical Society (ACS) Version Author's final manuscript Citable link http://hdl.handle.net/1721.1/106513 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. Concentrating Solar Power Lee A. Weinstein,1 James Loomis,1,2 Bikram Bhatia,1 David M. Bierman,1 Evelyn N. Wang,1 and Gang Chen*,1 1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. 2Department of Mechanical Engineering, University of Auckland, Auckland 1010, New Zealand. Table of Contents 1. INTRODUCTION ................................................................................................................................ 3 1.1. CSP Configurations ...................................................................................................................... 6 1.2. Maximum efficiency of a CSP system ........................................................................................ 13 2. CONCENTRATOR/REFLECTOR .................................................................................................... 15 2.1. Concentrator characteristics ........................................................................................................ 16 2.2. Optical properties and characterization ....................................................................................... 19 2.3. Reflector materials ...................................................................................................................... 22 2.4. Reflector degradation .................................................................................................................. 27 3. RECEIVER/ABSORBER ................................................................................................................... 30 3.1. Receiver efficiency ..................................................................................................................... 30 3.2. Spectrally selective surfaces ....................................................................................................... 33 3.2.1. Intrinsic absorbers ............................................................................................................... 42 3.2.2. Cermet absorbers................................................................................................................. 42 3.2.3. Semiconductor absorbers .................................................................................................... 45 3.2.4. Thin-film multilayer absorbers ........................................................................................... 46 1 3.2.5. Structured surface absorbers ............................................................................................... 47 3.2.6. Photonic crystal absorbers .................................................................................................. 47 3.3. Angularly selective surfaces ....................................................................................................... 49 3.4. Receiver technologies ................................................................................................................. 50 3.4.1. Vacuum tubes ...................................................................................................................... 50 3.4.2. LFR receivers ...................................................................................................................... 53 3.4.3. Central receivers ................................................................................................................. 54 4. HEAT TRANSFER FLUID ................................................................................................................ 57 4.1. Desired characteristics and figures of merit ................................................................................ 58 4.2. Types of heat transfer fluids........................................................................................................ 61 4.2.1. Oils ...................................................................................................................................... 62 4.2.2. Molten salts ......................................................................................................................... 65 4.2.3. Other liquids ........................................................................................................................ 68 4.2.4. Pressurized gases................................................................................................................. 72 4.2.5. Steam ................................................................................................................................... 74 5. Thermal Energy Storage ..................................................................................................................... 75 5.1. Sensible storage .......................................................................................................................... 79 5.2. Latent storage .............................................................................................................................. 85 5.3. Thermochemical storage ............................................................................................................. 90 6. HEAT ENGINE .................................................................................................................................. 93 6.1. Heat engine efficiency ................................................................................................................ 94 2 6.2. Novel cycles ................................................................................................................................ 96 6.2.1. Supercritical steam .............................................................................................................. 96 6.2.2. Supercritical CO2 ................................................................................................................ 97 6.2.3. Combined cycles ................................................................................................................. 97 6.3. Direct heat-to-electricity conversion ........................................................................................... 98 6.3.1. Solar Thermoelectric Generators (STEG): .......................................................................... 98 6.3.2. Solar Thermophotovoltaics (STPV):................................................................................. 100 7. CONCLUDING REMARKS ............................................................................................................ 103 8. AUTHOR INFORMATION ............................................................................................................. 104 8.1. Corresponding Author .............................................................................................................. 104 8.2. Notes ......................................................................................................................................... 104 8.3. Biographies ............................................................................................................................... 104 9. ACKNOWLEDGEMENTS .............................................................................................................. 106 10. REFERENCES ............................................................................................................................. 106 1. INTRODUCTION Solar energy is a bountiful renewable energy resource: the energy in the sunlight which reaches Earth in an hour exceeds the energy consumed by all of humanity in a year.1 While the phrase "solar energy conversion" probably brings photovoltaic (PV) cells to mind first, PV is not the only option for generating electricity from sunlight. Another promising technology for solar energy conversion is solar-thermal conversion, commonly referred to as concentrating solar power (CSP).2 The first utility-scale CSP plants were constructed in the 1980s, but for the following two decades CSP saw little expansion.3,4 More recent 3 years, however, have seen a CSP renaissance due to unprecedented growth in the adoption of CSP.3,5 Photos of two operating CSP plants, a parabolic trough collector plant and a central receiver (or "power tower"), are shown in Figure 1. Figure 1 Photos of two CSP plants: a) Solana Generating Station (proprietary technology of Abengoa Solar, S.A.), a parabolic trough collector plant in Phoenix, Arizona (original photo by James Loomis) and b) Solar Two, a "power tower" plant near Barstow, California. Reprinted with permission from reference 6. Copyright 2015 Elsevier. There are five steps to a conventional CSP system (illustrated in Figure 2): 1. Concentration: sunlight incident on a large concentrator is redirected to a much smaller receiver 2. Absorption: sunlight incident on the receiver is converted to heat by an absorber 3. Transfer: heat is carried away from the absorber by a heat transfer fluid (HTF) 4. Storage: heat