> Thirdly, the best annual storage is pumped hydro. It's the cheapest and it can be used pretty much everywhere -- all you need is water at one end of an elevat

> Thirdly, the best annual storage is pumped hydro. It's the cheapest and it can be used pretty much everywhere -- all you need is water at one end of an elevation change and a way to build storage at the other end. Pumped hydro is primarily used for short term storage. The vast majority of pumped hydro installations around the world operate on an intra-day cycle. For storage systems generally (not just electricity), profitability is a linear function of capacity, the possible price arbitrage AND how frequently you charge and discharge. Nobody is going to build a pumped hydro storage facility with the intension of operating a single charge/discharge cycle per year. Nor are pumped hydro facilities cheap to build and certainly cannot be deployed everywhere as they require particular geographic and geologic conditions and mostly locations suitable for pumped hydro are few and far between and those locations that are suitable are generally far away from population centers where the demand for electricity is. Batteries are often cheaper than pumped hydro, they can be located near demand, they scaled down as well as up and can be distributed around the grid to provide "virtual transmission". They are quick to deploy and require little maintenance or staffing. The solution for "long term" storage will be massive over-provision of wind and solar and more grid interconnections. Batteries will take care of everything else.