There are several paths to Solar Production of H 2 ApproachStatusProspects Electrolysis using solar electricity – solar PV, solar thermal, wind, etc. C$$ PhotoelectrochemicalR? Photobiological processes – algae, bacteria R? Biomass processing – gasification, pyrolysis; energy crops, waste R, DWaste is promising Thermochemical Water-splittingDAppears promising 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: H 2 O + Zn ZnO + H o C ZnO Zn + ½ O o C H 2 O H 2 + ½ O 2 All chemicals recycle, water is decomposed. Potential efficiency increases with (1-T cold /T hot ) 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 Advanced tower o CDish o C

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