Clean energy from water and the sun
An important step toward a hydrogen society was made on Monday, March 31, by a Greek research team from Thessaloniki working in Spain which held its first official demonstration of a pilot-scale solar reactor at Spain’s Almeria Solar Platform. The project produces clean energy in the form of hydrogen exclusively from water and the sun without emitting any pollutants or greenhouse gases. The efficiency of converting the solar energy is as high as 70 percent and appears to be the answer to the difficult problem of producing economically efficient hydrogen from renewable energy sources. It is the largest solar reactor in the world (producing 100 kilowatts) and has therefore attracted the attention of researchers and investors from around the world, as well as favorable commentary, such as a recent review in the April issue of Chemistry World. At the heart of the program is the HydroSol group, awarded the Descartes Prize for 2006 for scientific research, coordinated by Athanassios Constantopoulos, director of the Chemical Process Engineering Research Institute based in Thessaloniki. There are two solar towers in Almeria, where dozens of lenses concentrate solar rays to create high temperatures. It is not a new invention – Archimedes used the same principle to set fire to the Roman fleet in antiquity. Modern solar collectors are naturally more efficient and can be directed to follow the sun’s changing course across the sky. What is truly pioneering about this project is the reactor (produced by the HydroSol team), which is situated at the point where the rays are concentrated. At the core of the reactor are two honeycomb-like ceramic chambers coated with oxygen-deficient ferrite structures containing zinc and nickel. At high enough temperatures (800-1,200 degrees Celsius) these materials strip water of its oxygen, leaving hydrogen gas to bubble away. The oxidized materials must then be recycled, driving off their collected oxygen as gas, in a separate reaction step at 1,000-1,200 degrees C. «The hydrogen produced can be channeled into a fuel cell to produce energy or to a combustion point. The hydrogen can also be stored, solving the problem of storing and transporting solar energy. Secondly, the reactor can be used to recycle carbon dioxide. The hydrogen, together with carbon dioxide, can produce new fuel (such as methane). So a reactor like this can be set up alongside units producing CO2. Thirdly, it can be used to desalinate water. It could be an integrated solution for the Greek islands, providing energy and drinking water just by using the sun and water.» The next step is upscaling to 1 megawatt. «Our dream is for HydroSol III to be made in Greece; the cost is not prohibitive – about 3 million euros for 1 MW,» said Constantopoulos. «The Public Power Corporation (PPC) or the Gas Corporation (DEPA) could take the initiative. For example, the prime minister talked about Thessaloniki’s Innovation Zone. A large solar reactor could be the zone’s keynote project.» As for why this has not yet happened: «There was some interest, a lot of politicians and people who make decisions have listened to us, but the main reaction was one of surprise, such as, ‘How on earth did you do it?’ It takes us a long time to understand and even longer to act.»
