Because conventional photovoltaic panels produce electricity directly from sunlight, the energy they generate must either be used as it is produced or stored – either in batteries or by using the electricity to produce a fuel that acts as a storage medium for the energy. Now U.S. and Swiss researchers have developed a prototype device that directly converts the Sun’s rays into fuels that can be stored, allowing the energy to be used at night or transported to locations where it is needed.

A BBC report citing a paper appearing in the journal Science describes how the prototype device uses a quartz window and cavity to focus sunlight into a cylinder lined with cerium oxide. Cerium oxide, also known as ceria, is hygroscopic (meaning that it attracts and holds water molecules from the surrounding environment) and will also absorb a small amount of carbon dioxide. As the sunlight heats the ceria, it thermochemically breaks down the water and carbon dioxide pumped into the cylinder to produce carbon monoxide and hydrogen that can be converted to a liquid fuel.

The resultant hydrogen could be used as fuel for hydrogen fuel cell vehicles such as those being developed by a number of automakers, including Hyundai and Honda, while a combination of hydrogen and carbon monoxide could be used to create syngas – a combustible gas that has less than half the energy density of natural gas but is often used as a fuel source or as an intermediate for the production of other chemicals. The researchers say the device can also be used to produce methane.

With cerium being the most abundant “rare-earth” metal, the developers of the device from the California Institute of Technology and the Swiss Federal Institute of Technology say it would be economically feasible to use the technology on a large scale.

Although currently, the prototype is not very efficient, with the fuel created harnessing between just 0.7 and 0.8 percent of the solar energy put into the device. This inefficiency is because most of the energy is lost through heat loss through the reactor’s wall or through the re-radiation of sunlight back through the device’s aperture. However, the researchers believe that a commercially viable device with efficiency rates of up to 19 percent is possible by using better insulation and smaller apertures.