Solar panels only need light to function, so they generate energy even in cloudy weather and cool temperatures. However, solar energy production in Finland is very insignificant in winter, as the solar panels are covered with snow for part of the winter, so that sunlight does not reach the surface of the panels. We always take this into account when estimating the  annual production of a solar power plant.  When no solar energy is generated, electricity is purchased, as normal, from the electricity network.