Problems and Opportunities for Solar Energy in Biomass, Pyrolysis, and Gasification

Abstract

Passive solar input for drying crops and wood already make a significant input to the US energy budget, and active solar drying, requiring temperatures below 200/sup 0/C, can easily make an important substitution for fossil fuels in drying. Pyrolysis of biomass typically requires less than 1.6 MBtu/dry ton at a temperature of 500/sup 0/C, and this could potentially be supplied by direct solar heating. The heat input is likely to be by indirect heating of a solid, liquid or gas heat-transfer agent. Fast pyrolysis requires modest heat inputs with high heat-transfer rates at temperatures over 900/sup 0/C and thus may be particularly suited to focusing collectors as energy sources. Char gasification, using steam or CO/sub 2/, requires large energy inputs at temperatures over 900/sup 0/C and thus is the least likely field of application of solar energy. Ultimately, the large scale application of solar energy to biomass pyrolysis and gasification will depend on the relative cost of direct solar versus biomass inputs. Biomass energy inputs now typically cost 1 to 3 $/MBtu; when direct solar heat costs begin to approach this level, we may begin to use direct solar process heat for biomass conversion.