Does pumped storage promote clean energy and reduce carbon emissions?
It actually has the opposite effect. A study of energy storage systems built to complement the Netherlands' wind program found pumped storage generally ineffective and unprofitable. The most significant finding of the Dutch study was that wind generators combined with energy storage resulted in increased pollution and CO2 emissions.
Their wind power was easily absorbed by the grid, while the storage plants turned out to be optimal for storing power from cheap coal plants and using it as a substitute for cleaner more expensive gas during peak demand. Because of the inherent losses with pumped storage, 25% more coal was used than would have normally been needed to produce the same amount of energy directly, .
Energy from wind and solar is expensive, its production costs subsidized. Natural gas power is less expensive and optimal for absorbing peak power demnds. Coal is the cheapest power and most profitable when genrated off peak and sold later at higher rates.