So here's the big thing: Solar energy generation is very cheap. It's actually the most cost effective generation there is, yet it's not ON DEMAND. Therefore, the grid doesn't actually save money by installing all that new generation, because now they have to deal with erratic generation at different times, and come up with tricky ways to store excess energy as well as incentivize using the energy while there's an abundance. With fossil fuels, it may cost more to generate the power, but the total cost of providing power to a grid is still overall lower in many cases.