Less expensive and cleaner than power plants that use fossil fuels, why are they not used on a larger scale?

If your talking about solar power its because its just not practical solar power doesnt put out nearly enough power for us to be able to run widespread as of yet new and more efficient solar power inc

Another cleaner and less expensive forms of energy (not fossil fuel) are not used on a larger scale because of many reasons. Society is accustomed to burning fossil fuels. To change to another better form of energy would be a huge shift in the way factories, car and our electricity are powered. Also, many fossil fuel companies do not want to be out of business so they attempt to bribe politicians and other public figures to spread false information that climate change is fake so the can continue to earn money disregarding the horrible effects it will have on the planet. 

10.4 is the answer for you