In many countries, long, dark winters limit the amount of solar energy that can be generated for much of the year. That's where the Underground Sun Conversion system comes in, as it's intended to use sunlight to help produce natural gas deep underground.
The technology has been patented by energy company RAG Austria. It is now being developed via a European Union project that includes several Austrian and Swiss companies and institutions, including Switzerland's Empa research institute.
The procedure begins in the summer, when surplus electricity generated by solar panels and wind turbines is used to produce hydrogen. More specifically, that electricity is utilized in an electrolysis process, to split water into hydrogen and oxygen. That hydrogen – along with liquid carbon dioxide – is injected into natural porous sandstone deposits such as depleted natural gas reservoirs, up to 1,000 m (3,281 ft) below the Earth's surface.
There, "in a relatively short time," naturally occurring microorganisms known as archaea metabolize the hydrogen and CO2 into methane gas and water. The methane is then pumped back up to the surface, where it can be used as the main component of carbon-neutral natural gas during the winter months.
RAG Austria has successfully demonstrated the basic principles, and has so far achieved a solar/wind-electricity-to-methane conversion efficiency of about 60 percent. The project partners are now further investigating potential sources of CO2 and surplus renewable energy, plus they're mapping out possible locations for Underground Sun Conversion plants.
Sources: Empa, RAG Austria, Underground Sun Conversion project
