Finland is still 25% oil for electric generation [1] (and almost 40% fossil fuel). That means a lot of the electricity to heat the sand still comes from oil. It makes me wonder if this is more efficient than just using oil heating. Or some hybrid approach that uses oil to heat the sand.
Of course there are other benefits: it's still a good way to level electric generation, which is important for e.g. nuclear plants and wind power.
[1]: https://ourworldindata.org/grapher/energy-consumption-by-sou...
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