The first pumped-storage hydroelectric (pumped hydro) plant was built in 1907 (some sources cite 1909) in Switzerland.
It was the Engeweiher pumped storage facility near Schaffhausen, Switzerland. This early installation used separate pumps and turbines to store energy by pumping water to a higher reservoir during periods of low demand and releasing it to generate power when needed.
- Reversible turbines (which could both pump and generate) became common in the 1930s, improving efficiency for later plants.
- The first major/large-scale pumped hydro plant in the United States was the Rocky River Plant in New Milford, Connecticut (completed in 1929 by Connecticut Light and Power). It created Candlewood Lake as the upper reservoir.
Pumped hydro remains the dominant form of grid-scale energy storage worldwide due to its reliability and capacity. Early European developments (especially in Switzerland, Italy, and Germany) led the way before wider adoption.
This battery’s “self-discharge” rate is the evaporation rate from the lake. It’s small (low surface area to volume ratio).