Solar-Thermochemical H2 is Investigated by Germans, Canadians, Florida Lab

COLOGNE - Taking another crack at a concept first tried some thirty years ago, researchers at the German Aerospace Center (DLR) here have produced hydrogen by thermochemically splitting steam via concentrated sunlight.

In Canada, meanwhile, similar work is being carried out by a Saskatoon company, SHEC Labs (Solar Hydrogen Energy Corp), of Calgary. Last month, the company announced it has signed a strategic partnership agreement with two other Canadian companies, Hydrogenics Corp., Mississauga, Ont., manufacturer of fuel cell and related technologies, and with Giffels Associates Ltd., Toronto, a company that previously has done feasibility assessment work for SHEC.

And late last month, the Florida Solar Energy Center (FSEC) Cocoa, FL announced that it, together with two other institutions, will receive almost $4 million from the U.S. Energy Department to study solar-assisted thermochemical water-splitting cycles.

DLR’s initial, presumably small, amounts of hydrogen were generated in mid-September via an existing solar furnace, one of ten worldwide, and a solar reactor designed especially for this project.

Because of the newness of the project, DLR so far can’t say how efficient the process is. Dr. Christian Sattler, DLR’s research manager for solar materials conversion, told H&FCL the team is in the process of analyzing the data right now, adding “in thermodynamic terms, we are expecting very high yields.”

One difference between the new work here and the original concept of direct solar water-splitting is that with the help of a two-stage chemical reaction, hydrogen can be broken out at lower temperatures: less than 1,400 deg. C., a temperature level that brings it closer to those occuring in some chemical and industrial processes.

Direct solar water splitting, with concentrated sunlight only and no chemical assist, is possible in principle but requires temperatures of between roughly 2,500 K and 4,300 K (2,227 deg. C and 4,027 deg. C). Usable steam-to-hydrogen conversion starts at the lower temperature and complete separation of hydrogen and oxygen occurs at the higher end, according to Sattler.

Thermochemistry comes into play via a two-stage process. In the first stage, metal oxides - various types of ferrites - coating a ceramic support structure are directly radiated, liberating hydrogen from the hot steam at temperatures of 600-800 deg. C by bonding the steam’s oxygen to the excited metal oxide lattice, according to a description of the process on DLR’s website.

Sattler says the ceramic structure functions as a volumetric absorber that utilizes solar heat. No photonic effect comes into play.

In the second step, the oxygen previously bonded into the metal oxide lattice is released again at temperatures of 1,200-1,300 deg. C., regenerating the metal oxide.

The ten-year-old solar furnace, key piece of equipment and the only one of its kind in Germany, produces the necessary temperatures, concentrating sunlight by a factor of 5,500. Total thermal output is about 25 kW.

One of the key issues being investigated is the longevity of various types of ferrites that are being tested. Sattler says it is possible to completely cycle the materials “several times, but after only one month, one can’t really say very much about long-term stability.”

Another problem that apparently is still unresolved is the question of avoiding the recombination of hydrogen and oxygen, something that had stumped previous efforts in this area. At these very elevated temperatures, the two gases tend to recombine immediately into steam again, and keeping them separate is very difficult. Sattler says industrial-scale separation of the hot gases is the goal, but indicates that for the time being at least, an economical solution isn’t in sight.

DLR is cooperating with Johnson Matthey, the British noble metals company which provides some of the ferrite materials. Another supplier of metal oxides is the Greek company CERTH/CPERI, the “Aerosol and Particle Technology Laboratory,” Thessalonika. A Danish company, Heliotech Aps, located near Copenhagen, contributed the extruded ceramics components that serve as carriers for the metal oxides.

The DLR work is part of the European Union’s HYDROSOL project, funded since November as part of the 5th R&D Framework Programme. Right now it is scheduled to run until October 2005, but the plan is to continue the work in a followup program.

SHEC’s website says the company has devised a solar thermochemical concentrator and a process capable of splitting hydrogen out from water at temperatures significantly below 1,000 deg. C. It said it produced hydrogen from water and concentrated solar power in two test runs in June at 850 deg. C. at the Solar Test and Research Facility operated by Arizona Public Service in Tempe.

Florida’s FSEC, meanwhile, said in its announcement it will be receiving $3.999,805 from DoE for a joint project with Science Applications International Corp., (SAIC) San Diego, CA and Universidad del Turabo (UT), Gurabo, Puerto Rico.

The funding is intended for a three-phase, multi-year r&d program leading to the demonstration of a cost-effective water-splitting cycle to make hydrogen, using state-of-the art high-flux solar concentrators.

In Phase 1, FSEC will assess state-of-the-technology for solar thermochemical cycles, and SAIC will work with FSEC to develop a preliminary design of the pilot-scale solar reactor and solar reactor and to perform economic analysis.

In Phase II, the team will develop a thermochemical reactor/solar receiver system for use with the selected cycle, test a bench-scale system, and develop a pilot-scale unit using a SAIC dish concentrator.

In Phase III, a 50 kWth solar-powered hydrogen production unit is to be installed and demonstrated, also in Tempe, AZ.

The project is one of 36 research projects due to receive $75 million under DoE’s Hydrogen Fuel Initiative announced last month (see DoE News, p.6). Contacts/Sources: DLR media, Hans-Leo Richter, 0049/2203/601-2425; web www.dlr.de; SHEC-Labs, www.shec-labs.com; FSEC, Debbie Rodgers, phone 321/638-1013, e-mail DRodgers@fsec.ucf.edu.