International solar thermal energy researchers have successfully tested CONTISOL, a solar reactor that runs on air and is able to run day or night because it uses concentrated solar power (CSP) and thermal energy storage to make any solar fuel. CONTISOL was tested at Cologne, Germany using simulated 'suns', rather than an actual solar field, and the storage and heat exchanger was also simulated, because the reactor itself is the innovation being tested. Courtesy of DLR. Solar fuels could result in zero-carbon fuels like hydrogen without the climate-damaging carbon emissions it takes to make hydrogen from natural gas. The development of solar reactors could lead to a 100 percent clean energy future. Instead of burning a fossil fuel for the heat needed to drive the thermal chemistry process, for chemical reactions like splitting hydrogen from water, scientists have been testing various kinds of reactors heated by CSP, which uses mirrors to concentrate solar flux on a receiver. To attain zero-carbon heat for thermochemical reactions – which can operate at temperatures as high as 1500° C – experts view the direct heat of CSP as a more efficient clean energy source than electricity from photovoltaics or wind. There will be an unlimited supply of sunlight over centuries, and no climate consequences when thermochemistry is driven by solar energy. The only disadvantage compared to burning fossil energy, is that the sun goes down at night. Now, a group of scientists at the German Aerospace Center (DLR) supported by the Aerosol and Particle Technology Laboratory of the Chemical Process and Energy Resources Institute of Greece have built and tested a new solar reactor design that includes storage so it can provide round-the-clock heat like the current fossil-fired method, but without the emissions. "Solar reactors in the past have had the problem of what you do at night when you don't have sun, or even when clouds go by," said Justin Lapp, lead author of a paper detailing the technology and assistant professor of mechanical engineering at the University of Maine. Lapp explained that when the temperature drops, the reaction could need to be halted or the flow rate of the reactants slowed, reducing the amount of products that you get out. If the reactor shuts down at night it cools off, not just wasting residual heat, but starting over from nothing next morning. By combining storage capabilities with a direct solar thermochemical reactor, stable temperatures are created around the clock with an efficient heat source to perform reactions.