Abstract
The design, fabrication, and on-sun characterization of a solar dish concentrating system for performing the two-step thermochemical redox splitting of H2O and CO2 is presented. It comprises a primary sun-tracking 4.4 m-dia. solar dish concentrator coupled to a secondary planar rotating reflector. This optical arrangement enables the operation of two (or more) solar reactors side-by-side for performing both redox reactions simultaneously by alternating the solar input between them while making continuous and uninterrupted use of the incoming concentrated sunlight. On-sun characterization of the complete concentrating system revealed a peak solar concentration ratio of 5010 suns and an average of 2710 suns measured over the 30 mm-radius aperture of the solar reactor. A detailed optical analysis elucidates measures to increase the optical efficiency and concentration ratio.
Highlights
Solar splitting of H2O and CO2 is performed using a thermochemical cycle based on the reduction-oxidation of metal oxides (Romero and Steinfeld, 2012), comprising two steps: (1) a high-temperature solar endothermic reduction step, and (2) a subsequent low-temperature exothermic oxidation step with CO2 or H2O to generate H2 and CO – syngas, the precursor of liquid hydrocarbon fuels
In the framework of the EU-project SOLARJET, we have experimentally demonstrated, at lab scale, the first ever production of solar jet fuel from H2O and CO2 via such a thermochemical redox cycle (Marxer et al, 2015)
Its thermal reduction proceeds to a reasonable extent at a temperature of 1500 °C (Panlener et al, 1975; Scheffe and Steinfeld, 2012). This corresponds to a required solar concentration ratio1 above 2000 suns for efficient operation (Romero and Steinfeld, 2012), which can be obtained by point-focus concentrating systems, either in centralized solar towers or decentralized solar dishes
Summary
Solar splitting of H2O and CO2 is performed using a thermochemical cycle based on the reduction-oxidation (redox) of metal oxides (Romero and Steinfeld, 2012), comprising two steps: (1) a high-temperature solar endothermic reduction step, and (2) a subsequent low-temperature exothermic oxidation step with CO2 or H2O to generate H2 and CO – syngas, the precursor of liquid hydrocarbon fuels. In the framework of the EU-project SOLARJET, we have experimentally demonstrated, at lab scale, the first ever production of solar jet fuel from H2O and CO2 via such a thermochemical redox cycle (Marxer et al, 2015) In this two-step cyclic process, only the first endothermic step requires concentrated solar energy as the source of high-temperature process heat. Its thermal reduction proceeds to a reasonable extent at a temperature of 1500 °C (Panlener et al, 1975; Scheffe and Steinfeld, 2012) This corresponds to a required solar concentration ratio above 2000 suns for efficient operation (Romero and Steinfeld, 2012), which can be obtained by point-focus concentrating systems, either in centralized solar towers or decentralized solar dishes. Line-focus trough and Fresnel systems are theoretically bounded by the much lower 2D-concentration limit of 215 suns compared to the 3Dconcentration limit of 46,250 suns (Winston, 1970), and are unsuitable for achieving the temperatures required for thermochemical redox cycles
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