>During the coldest, most expensive stretch, the wood chip boiler became the primary unit, and the sand battery supplemented it.
Remarkably: heat is pointed to as "wasted energy" when doing EROEI analysis and discounted, this is done to strengthen the case for Solar vs Gas.
Finland's energy mix is ~6% solar [1]... maybe it's not a larger portion of the grid supply because Finns realize it doesn't work in the winter?
In any case, Finland does not really use fossil fuels for electricity generation anymore. There is some cogeneration, where heat is the primary output, and reserve power plants that are only used in exceptional situations. Electricity is largely a solved problem, but it's proving harder to get rid of fossil fuels in heating and transportation.