Each of the 64 slightly curved heliostats of the Weizmann solar tower concentrate solar radiation by a factor of about 50 for a combined total of about 3,000 suns. Kogan and his team overcame the problem by refocusing the 50 x enhanced radiation from only one heliostat with a secondary concentrator, a small 63 cm parabolic mirror. The experimental reactor is located near the focal plane of this secondary mirror. The end of the housing facing the mirror is closed by a circular disc with a small central aperture. A porous zirconia membrane is installed at the opposite end of the housing.
Superheated steam is fed into the reactor cavity.
In the past, much work has been devoted to the method of rapid quenching of the hot gas effluents from the reactor, Kogan explained, to keep them from re-reacting with each other, making steam again. Instead, Kogan concluded early on, the only chance to develop hydrogen production by solar thermal watersplitting into a thermodynamically efficient process is by separating hydrogen from the mixture of water-splitting products in place while the gas mixture is still hot, and by recovering heat from the effluent gas as well as we can. Taking a cue from nuclear fuel processing technology, Kogan decided on a gas diffusion process through a porous ceramic membrane where the difference in molecular weights of hydrogen and oxygen and the different speeds with which they diffuse through such a membrane makes gas diffusion very effective in our case. Such an injector is now being developed together with the aerospace engineering department of Israel s Technion-Israel Institute of Technology. The new effort follows two main approaches.