Conventional reservoir-backed hydroelectric dams can be throttled up and down pretty quickly, and can't run at 100% around the clock without depleting the reser

Conventional reservoir-backed hydroelectric dams can be throttled up and down pretty quickly, and can't run at 100% around the clock without depleting the reservoir. The Hoover Dam has an annual capacity factor of only 23%, for example. As solar gets cheap I think that the most cost-effective way to firm it up is to install it connected to the same transmission capacity as an existing hydroelectric project, and throttle the hydro output down when solar generation is strong. There are limits to how much down you can throttle a dam of course. Still it can serve as a hybrid system that marries solar scalability and hydro reliability without paying for battery storage.