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Then you'd end up making strong walls to keep the surrounding soil out when the bin is empty

The ground is.... 4C or something? Would it lose more heat more easily to the solid ground, than to the air?

Its probably easier to keep it dry above ground too.

I got interested in this tech a while back myself (thinking I should build one myself, how hard can it be?) and I made some simulations (because who wouldn't). The thermal gradient in sand is actually quite steep, even with very high temps around the core where the resistors are, the temps fall off pretty quickly. Then when you are at a point where the surface temp is reasonable, you switch to a conventional thermal insulator. Putting it underground would cause all sorts of issues in eg. maintaining the resistors, insulation etc. so it's probably just easier to do it like this.

Maintenance? Might be easier above ground, but I know nothing of the tech, so I could be completely wrong 😞

this battery makes sense only in colder climates

Almost as if there's a reason it's happening in Finland...

Anywhere with municipal heating really.

I can see the middle being 600C, the edges are probably cooler.

Its a thermal storage battery, no electricity is generated.

Insulation and the thermal properties of sand ie it is good at storing heat. Think of it like a rock, it can store tons of heat but it takes a long time to transfer heat.

THIS IS NOT A BATTERY.

‘Battery’ is the name for any device that stores any energy. It doesn’t have to be electric energy.

Seebeck generators exist.

Yes, and the basic principle of thermal batteries has been quite common here in Finland for some time.

All Finnish cities have district heating networks, so there is some heating plant that generates heat, which is distributed to homes using water as medium. It is closed system where hot water goes in, colder water comes out, which is heated back up. This energy is used to heat the home and heat the cold usage water (faucet/shower etc)

Because the network is lots of water, there is already quite a lot of energy storage in the heat grid itself, so itself works as a battery. In last five years almost all big networks have created water based thermal batteries. Those are 7-8 stories high insulated water containers. These make sense because you just start taking the already heated water from the container to the grid when ever you need.

So the tech itself is quite standard here, just the medium of using sand is new. Sand brings you bit longer storage time, but adds bit of complexity to the process.

Source: I work in a company that owns these kind of networks

There are other methods, but they're far less efficient.

Solar panels convert light, not heat, into electricity. Specifically, photons (light) excite electrons in the solar cell, and these excited electrons then move through the solar cell and form a current.

This isn't really being used to generate electricity. They're developing a generator from it, but currently it's used for purely thermal energy transfer. Basically, the towns have big pipes running through them for communal heating, and these pipes are heated by this thermal energy storage.

I imagine they're only talking about electricity generation as an extra revenue stream for their customers who buy these, rather than it being a good solution for storing and generating electricity. The 90% efficiency is much better than combustion generators, but far worse than true electric batteries.

It is incredibly efficient at huge scale.

Large scale three phase energy generation is always something rotating in sync with the grid. Easiest way to do that is to spin turbine+generator.

All nuclear, coal, biomass power plants just heat water to 300-800°C and push it through turbine.

The thing is that it is really quite robust, and there isn't any other good solutions to it. They do have quite a lot of loss, but the cooled water after process (still over 100°C) can be used in other industries or district heating improving the efficiency.

Hydropower just spin the turbine with water flow. Wind directly spins the turbine, which is good for efficiency. Solar panels are still quite inefficient, but because they just use space, they make lot of sense even with poorer efficiency.