4c524e74_y_Storage____Clean_Energy_Wonk__1
[0] Pumped Hydro: Reservoir to Reservoir [2] The cheapest and most developed technology, pumped hydro is nevertheless limited by the availability of suitable sites. [3] $3-$50 per kWh; 70% to 85% [4] The major supplier in the business is private. Could look for opportunities in utilities that have good potential projects. [1] 
Energy is stored by pumping water from a low reservoir to a higher one, and recovered by running the water back out through a turbine. This system can be easily retrofitted into existing reservoirs, but has limitations due to water regulations. First used in 1890.
Large Scale Electricity Storage. | Clean Energy Wonk
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