Finland only started building solar recently. Wind is still more cost-effective, if you only consider the cost of generation. But there is almost too much installed wind capacity. If you also consider the value of the generated energy, solar gets ahead, as it correlates less with existing generation.

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.