Underground Sun Conversion tech uses sunlight to produce natural gas

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.

A diagram outlining the Underground Sun Conversion process
RAG Austria

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

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Dave Holland
Hmmm.... It would be interesting to see a comparison with just using the H2 as 'fuel'. Also, the "...solar/wind-electricity-to-methane conversion efficiency of about 60 percent" is ambiguous at best. IMHO
Solar and Wind to electricity are less than half that but let's call it 30%. Then you produce H2, let's say 80% efficient, gives you less than 24% solar to hydrogen. Then you have some energy costs to extract and compress CO2 from somewhere, then put it in the ground and wait, so we have less than 24% solar to methane efficiency.
So I guess they mean 60% of "electricity to methane", in which case the wind/solar words are irrelevant (and also a little confusing/misleading).
Also, if you want electricity from the methane you then have to run a gas fired system to produce it, taking off another, say, 70% so you end up with less than 7% solar to electricity - all to be carbon neutral.
This is a real Rube Goldberg way of producing "clean" energy. Grid level storage technology is being built out as I write this,with the most notable examples being liquid air storage (Highview Power) and flow batteries (Ambri). They both are designed to store excess solar/wind in an efficient way.
Earlier posters have evaluated the technology very well. However, they didn't consider the real purpose of the project, which is to generate a lot good press and then some great government subsidies. There's a lot of money to be made in APPEARING to be green.
So they convert a clean gas (hydrogen) into methane, a gas dirtier than carbon dioxide, all pumped into underground. What could go wrong?
piperTom...correct. None of these will ever produce more than ideas.
In any case, a renewable source of home/business heating/cooking fuel seems like it would have benefits. The distribution system is already in place in many locations. And that distribution system can make direct use of hydrogen right now. Efficiency isn't so important when the energy source at the top is free.
The deerhunter
Certainly a clumsy and roundabout way of utilizing surplus green energy to shuFFle waterand CO2 around to create an even worse greenhouse gas.
Awesome - Nice write up Ben.
On the farm I played around with methane generators and used the waste product as rich compost and compost tea. I collected the methane in an old truck inner tube. Didn't want or have access to pumping the methane produced into the rock strata where H2 and CO2 could make combine with biological enzymes producing propane, butane, and so forth.
Not on the farm with horses and cows to produce the "raw" materials, and I'm not big on splitting water today to use 6 months from now - but what a great plan.
What happens when someone drills across into their strata of rock and pull the "un-natural gas" out of it before the pumper folks get it out?