A review of solar thermochemical processes

This paper reviews development in the field of solar thermochemical processing by considering experimental demonstrations, reactor technology development, thermodynamic, economic and life cycle analyses. The review then builds on these aspects and compares various solar thermochemical processes. Solar upgrading of carbon feed has been demonstrated on pilot scale. It is observed that for the thermochemical cycles, only iron and ceria based redox pair have been demonstrated on pilot scale. For industrial applications, solar thermochemical production of zinc, upgrading of landfill gas and organic waste have been demonstrated on pilot scale. However, long term performance data of these pilot plants is not reported in literature. Thermodynamic comparison reveals that the processes involving upgrading of carbon feed have energy and exergy efficiency at 50-90% and 46-48% respectively. Multistep thermochemical cycles operating at 9001200 K have energy efficiency of 34-38%. Metal oxide redox pair based thermochemical cycles operating at 1900-2300 K have energy and exergy efficiencies of 12-32% and 20-36% respectively. Methane reforming and lime production processes have chemical efficiencies of 55% and 35% respectively and have demonstrated better performance than other solar thermochemical processes. A few processes like solar gasification of solid carbon feed have demonstrated lower chemical efficiency of around 10% even at pilot scale. The hydrogen production cost for solar upgrading of fossil fuels is estimated at 3.21-6.10$/kg and is lower than thermochemical cycles at 7.17-19.26$/lcg and CSP driven electrolysis at 3.15-10.23$/kg. It is observed that there is limited actual data and significant uncertainty in cost. Under these circumstances, it is recommended that initial screening of processes be done by net energy, material and life cycle analysis. (c) 2015 Elsevier Ltd. All rights reserved.