For reference, the price for fixed-cost plans is around 10c/kWh.
As someone who’s been constantly running an electric heater in the garage while painting my car, I was quite lucky with the timing.
It’s not literally free, though. Transfer prices are fixed, and there are taxes and some other minor costs associated with it, so where I live, it still adds up to around 6c/kWh even when the price drops to zero. The cheap prices are due to an excess of wind power, but once the wind dies down, prices usually spike hard.
It’s fair pointing out the lack of (sufficient) storage for electric energy, but I’d say the average price of electricity in Finland for the past week indicates both capabilities of renawables and lack of storage.