These sites are off-river closed-cycle projects: you do not need to interfere with river flows or ecology significantly, and only need a modest stream to top up evaporation losses. Pumped hydro has numerous advantages over other forms of storage: it is a fully mature, century-old technology with known costs; it is the cheapest form of large-scale storage; and in construction it creates many manual jobs whose profile is a pretty good match to underground mining. The main disadvantage is that like all large-scale construction, a pumped hydro scheme takes some time, say five years from investment decision to completion, But that turns into a plus for the jobs. Pumped hydro spans a wide range of economic sizes, from 100 MW or so to to the3 GW behemoth at Bath County and Fengning..