This sand battery compensates for the major shortcoming of green energy

More and more researchers are interested in non-chemical batteries to support the ecological transition.

To achieve our ecological objectives, it becomes essential to rethink the way we produce and use our energy. But it also means developing new ways to store it. Finnish researchers spotted by the BBC have installed the very first battery of a new kind: it is an accumulator that works with sand and heat.

At first glance, this association might seem absurd, but it nevertheless rests on solid foundations. Very briefly, a battery is neither more nor less than a potential energy reserve, that is to say energy that can be restored in another form at the end of a conversion. The most explicit example is surely that of the spring ; it accumulates potential energy when compressed and releases it mechanically when released.

In a standard accumulator, this potential is chemical. The energy is returned in the form of electricity through a reaction that involves the anode, the cathode and the electrolyte. But in theory, this potential energy does not have to be chemical. As long as we can find a way to convert one energy into another reversibly and with good efficiency, then we eventually have a battery.

Alternative batteries at the service of renewable energies

For example, a huge battery that uses gravitational potential energy has just opened at Nant de Drance in Switzerland (see our article). To return energy to the system, engineers open valves that drain a reservoir of water to a reservoir below. Under the effect of gravity, this water will also set turbines in motion, which corresponds to the return of electricity.

© Nant de Drance

The main interest of these systems is that they are a perfect complement to renewable energies who are on the rise at the moment. These tend to be by definition intermittent ; the balance of wind energy remains zero as long as the air is calm, like that of photovoltaics during the night, and so on.

With such technology, it is possible to store this energy during production peaks, when it is abundant and by definition inexpensive. It can then be returned during low periods, when the weather is less favorable and prices higher. And all this without the use of traditional chemical batteries.

Sand instead of acids

This is also the objective pursued by the Finnish engineers with their battery. But here the concept is different again. To begin with, it does not rely on chemical or gravitational potential. Instead, engineers use large resistors to heat the contents of a tank of about 100 tons of sand.

Electrical energy from photovoltaics and other renewable energy sources is therefore stored in the form of heat. And contrary to what intuition might suggest, it can remain in this form for a long time.

This sand has a very high specific heat capacity. Very vulgarly, this means that he can store a large amount of heat and the keep for a long time (several months according to the researchers) with almost negligible losses.

More and more innovative new technologies are now competing with standard chemical batteries. © G.M.G.

A clean, economical and already functional system

The other particularity of this system is that it does not convert this heat back into electricity at the end of the chain. Instead, it is used as is. During periods of low demand, the accumulated heat can be directly used to supply the municipal heating system. It then helps to heat homes, offices, public buildings… and even the local swimming pool.

For now, everyone is satisfied with this very environmentally friendly system. And according to those responsible for the project, all the conditions have already been met to deploy this technology wherever renewable energies are well established. One can even imagine systems of this kind on the scale of an individual house.

Potential in the industry

Moreover, this does not only concern individuals and municipalities. L’industry could also very well use these systems. This would promote the use of green energies in branches where the intermittency of renewable energies would force the operator to invest in huge chemical batteries, which is often economic nonsense and an ecological aberration.

The other very interesting aspect in this industrial context is that such a battery could even make it possible to store a small part of the residual heat produced by the normal operation of a factory!

But to achieve this, there is still work to do. The next step will be to check whether this concept could be viable on a very large scale, with several hundred or even thousands of tons of sand.

The researchers also intend to explore the technical feasibility of conversion to electricity. For now, the yield from this operation remains ridiculously low, but the researchers are relatively optimistic.

It will therefore be interesting to see how far they can push their concept, and if other local authorities are tempted.

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