If the sun isn't shining and there isn't sufficient buffered storage (batteries, etc) then even if the solar panels are a penny each, their kwh costs are infini

If the sun isn't shining and there isn't sufficient buffered storage (batteries, etc) then even if the solar panels are a penny each, their kwh costs are infinite until the sun shines again. If you can cover 95% of the time but still need a natural gas power plant for the last 5%, you haven't saved any money except the cost of the natural gas itself. In the US, it is stupid cheap, so you haven't saved much at all.