What if we could store heat for the winter?

As Chris Goodall reports in his book The Switch, 80% of the world could run quite happily on solar power and batteries. There is enough sunlight per capita, and energy needs are modest enough for solar power to be the dominant form of energy.

The 20% that can’t rely on solar alone are predominantly the countries of the Northern hemisphere. They need a lot more energy in winter. Britain is one of those countries.

I can observe this with my own rooftop solar. A long summer day can provide five times more power than we need as a household. In winter, the grey skies and shorter days don’t provide enough to meet our electricity usage, let alone our heating needs. It’s not there when we need it most.

Scaling this up across the country, there’s a huge seasonal gap in energy demand. Wouldn’t it be great if we could bank a big store of energy to use in the winter? This is what we northerners have done with food for thousands of years, after all – building up a food stock to see us through the lean months. Is there any way to do it with energy?

One medium scale way to do it is with seasonal thermal energy storage, which captures heat in the summer and stores it underground for use in the winter. Heat can be stored in an earth bank, a borehole or a water tank in the foundations of the building. Heat pumps then extract the warmth when it is needed and run it into the heating system.

I’ve written about buildings with heat storage before. This office in Amsterdam stores heat in an aquifer, this one in Adelaide banks heat in an underground pit full of gravel and water. As you can imagine, this isn’t exactly something you can retrofit to your home. Ideally it would be designed in at the start. And it works best at a medium size – I’ve heard of it in offices and schools, and used in district scale heating systems.

Another option is to store energy as gas. Surplus renewable energy can be turned into hydrogen through electrolysis. The hydrogen could then be used for transport, or electricity generation. It could provide electric heat, or be pumped into the gas grid. The Institute of Mechanical Engineers suggests that with a few tweaks, Britain’s gas grid could handle concentrations of 20% hydrogen.

This is already being done in a variety of places around the world. I recently made a (very small) investment in a project in the Orkney Islands that uses tidal power to create hydrogen.

One larger scale option is being investigated in Austria at the moment. A gas storage company were experimenting with storing hydrogen underground in porous rock. They discovered – apparently by accident – that by pumping in CO2, they could recreate the natural process that makes methane. By combining hydrogen from renewable energy and captured CO2, they could make carbon neutral natural gas, a process they have named ‘underground sun storage‘.

It’s still at the experimental stages, but it’s an interesting idea. RAG Austria reckon their system could provide 400 times more storage than all the country’s pumped energy storage combined. If it works, we might one day be able to store vast quantities of clean natural gas in old gas fields. At that point, perhaps we’ll be closer to a national energy store to get us through the winter.


  1. I don’t understand the chemistry of how that works, but turning CO2 into methane sounds like a great idea. Hopefully it is a profitable process.
    I hear a lot of talk about carbon capture, but this is this first I have heard of using the gas instead of just tucking it away and hoping it doesn’t escape.

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