I have always found pumped-storage hydropower to be a fascinating technology.
According to Wikipedia, the first use of pumped storage was in the 1890s in Italy and Switzerland. And the first pumped-storage plant built in the U.S. was in 1930 by the Connecticut Electric and Power Company, using a reservoir near New Milford, Ct., and pumping water from the Housatonic River. Reversible turbine-generator units became available in the 1930s.
Since that time, pumped storage has evolved significantly. There is a fascinating pumped-storage plant in Okinawa, Japan, that uses the Philippine Sea as its lower reservoir. And in May, Norwegian scientists unveiled a concept for a pumped-storage facility on the ocean floor!
A new technology that is showing a great deal of promise for existing as well as new pumped-storage facilities is variable speed units. With these units, the speed can be varied through a frequency converter, allowing a change in the discharge/power in pump mode. And in turbine mode, the unit can operate at peak efficiency over a larger portion of its operating range. By comparison, with fixed speed units, there is only one operating point for a given head. This technology has been used for several years, particularly in Japan, and shows promise in dealing with the rapid growth of intermittent power sources, such as wind and solar.
Pumped storage is enjoying some time in the spotlight these days, due in part to the fact that it is the only technology available to store electricity economically and on a large scale. Sure, there are other storage options available, and these include batteries and compressed air. However, a study recently released by scientists at Stanford University revealed that when looking at energy return on investment of wind and solar resources, large-scale geologically based storage technologies such as pumped-storage hydro and compressed air provide a much higher return than electrochemically based storage technologies such as batteries. The obvious limitation with compressed air storage is the fact that there are only two operating plants of this type in the world according to Pacific Northwest National Laboratory, the largest having a capacity of 290 MW.
Compare this with the sheer number and size of pumped-storage projects being built worldwide. For example, Indonesia is working on construction of the 1,040-MW Upper Cisokan project on the Cisokan River in West Java. In October, an inauguration ceremony was held to mark the completion of the2,000-MW La Muela project in Spain’s Jucar River Basin. And in September, Quarry Battery Company received planning permission to develop the 49.4-MW Glyn Rhonwy project in a former slate mine in Wales.
Another boost to pumped storage, in the U.S., is recent legislation passed that requires the Federal Energy Regulatory Commission to examine a two-year licensing process for closed-loop pumped-storage projects. FERC defines closed loop as those projects that are not continuously connected to a naturally flowing water feature.