> 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.

> 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. This is not a valid conclusion. Battery projects like this are gonna charge/heat up when the electricity price is low, electricity price is low when supply/demand ratio is high and this often happens when renewable electricity is most available and makes up a disproportionate share of the electricity mix. Edit: Your graph is not what you say it is, this shows primary energy (i.e. includes fuel/heating/...), not "electric generation". Electricity in Finland is mostly nuclear, wind, hydro and certainly not "40% fossil fuel".