Fundamentally? Nothing. They are good and should be used whenever and wherever possible. There is a number to consider when doing this planning - it's called

Fundamentally? Nothing. They are good and should be used whenever and wherever possible. There is a number to consider when doing this planning - it's called the capacity factor. https://en.wikipedia.org/wiki/Capacity_factor https://en.wikipedia.org/wiki/Capacity_factor > The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. In the US for 2018 data Nuclear: 92.6% Conv. Hydro: 42.8% Wind: 37.4% Solar PV: 26.1% Solar CSP: 23.6% Landfill Gas: 73.3% Other biomass: 49.3% Geothermal: 77.3% Coal: 54.0% Natural Gas CC: 57.6% Natural Gas CT: 11.8% Natural Gas ST: 13.7% Oil ST: 13.9% Oil CT: 2.5% Hydro has a bit of variability that can get it better than nuclear if it has a retention dam rather than run of the river. Hydro may also be impacted by other regulations regarding excessive aeration of the water and fish spawning times (https://www.theatlantic.com/technology/archive/2011/06/massive-snowmelt-pits-wind-turbines-against-water-power/240373/ https://www.theatlantic.com/technology/archive/2011/06/massi... https://www.seattletimes.com/seattle-news/wind-power-and-water-power-collide-in-northwest/ https://www.seattletimes.com/seattle-news/wind-power-and-wat... ) This also depends on the month of the year (hydro provides more in the spring than in the fall, solar provides more in the summer than in the winter). The installed capacity of solar provides only a fraction of what it theoretically could in the winter when the days are shorter and the sun is lower in the sky.