Half of all our energy is used as heat and, both across the world and here in the UK, most of that comes from fossil fuels.

While in Britain we have more than halved the carbon in the electricity flowing through the wires, the climate impact of heat has proved much harder to melt away.

But a thaw is coming which needs two components: available cheap renewable energy and a rechargeable heat battery, which is quick to charge and with scalding temperatures available on tap.

At Caldera, a growing British company with 20 employees based in Hampshire, they believe the answer lies in a big lump of basalt gravel bound together by aluminium.

The metal comes from scrapped car engines, as in recent years the heavy bit which houses the cylinders has been made from aluminium. As we move towards electric cars, many more of them will be in the junk yard.

These ingredients are available, relatively cheap and, most importantly, effective.

Lisa Tidswell, their head of supply chain, says the basalt is very good at holding heat while the aluminium is very good at conducting it.

"To get the heat in we use an electric element like a bigger version of what you have in your kettle or immersion heater," she says.

"We then hold the energy in the thermal block which will weigh over a tonne. And then we take the heat out using a coil of stainless steel (which runs through the block). Water goes in one end and steam at up to 200C comes out the other."

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Many industrial processes, especially in the food and drink sector need those sorts of temperatures for brewing, distilling, pasteurisation and sterilisation.

The company is even in discussion with the management of a big hospital, who think solar and storage may be the best solution for their massive heat and cleanliness requirements.

The company's chief executive, James MacNaghten, walked me through a bank of 10 batteries, cylinders about two metres high and nearly one metre across.

"We heat the centre up to 500C and we keep the heat in there with the vacuum insulation which is around them. Placed next to a factory, they can produce heat on demand for whatever process they need," he says.

"We can take really large chunks out of their energy demand in a very short period of time. I think it (heat storage) has a huge role to play around decarbonising heat. It would be like taking 40% of cars off the road."

But where does their source electricity come from in the first place?

Caldera suggests factories build their own solar farms or wind turbines and have heat batteries to soak up the surplus electricity on windy nights or very sunny days.

This allows the system to be self-contained and not dependent on permission from the National Grid - something frequently not granted as they worry about power surges harming the network.

The other option is taking excess energy from the grid itself. As our power comes from more unpredictable renewable sources, we need to be able to store the excess.

Iain Staffell, from the UK Energy Research Centre at Imperial College London, says this will be increasingly attractive.

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"Even now we've got times on the system when wind is providing more than half of our electricity and the power price is negative," he said.

"So, if you can consume electricity, you actually get paid for doing it. Last week, you could have got paid £88 for consuming a megawatt hour of electricity. Heat storage is also really different: as you can store energy for days or weeks, say from when a big storm was passing through, for use when we don't have enough."

Storing renewable power in powerful affordable electric batteries has proven a vital first step in decarbonising energy.

Storing heat is step two.