Transcript Slide 1
There are several paths to Solar Production of H2 Approach Status Prospects C $$ Photoelectrochemical R ? Photobiological processes R ? R, D Waste is promising D Appears promising Electrolysis using solar electricity – solar PV, solar thermal, wind, etc. – algae, bacteria Biomass processing – gasification, pyrolysis; energy crops, waste Thermochemical Water-splitting R: Research D: Development C: Commercial Costs of biomass production and collection are high; use waste materials • Ethanol from corn currently uses more fossil energy to produce than it contains • Cellulosic ethanol processes could use agri-waste • Supercritical Water Partial Oxidation of municipal waste appears promising – Convert waste to resource – Residue is clean and safe – Application to California Hydrogen Highway? Thermochemical water-splitting can use the high temperatures solar energy can provide • Example: H2O + Zn ZnO + H2 ZnO Zn + ½ O2 H2O H2 + ½ O2 500oC 2000oC • All chemicals recycle, water is decomposed. • Potential efficiency increases with (1-Tcold/Thot) per Carnot. • Over 300 cycles exist; which are best for solar? DOE project reviewed candidate cycles • Is the process “practical”? – Simplicity, Economics, Solar compatibility, Knowledge base, Safety • Does it have potential for high efficiency? – 10 cycles selected, efficiency ~40 to 80% possible • Laboratory verification now underway • Pilot plant design will be done for best cycles Dish 650-1125-2250 oC Advanced tower 500-875-2000 oC Example: Cadmium cycles are potentially attractive • Cadmium oxide cycle • Cadmium carbonate cycle • Cycles are simple with no side reactions • Aspen flowsheets indicate efficiency up to 71% • Cost estimates are encouraging Solar-based Hydrogen Production has a role • DOE-supported research is underway on several pathways, most not yet ready for application • Waste biomass could be implemented now on a developmental basis • Solar thermochemical processes appear promising, could be implemented soon • California Hydrogen Highway could demonstrate these processes