Pumped hydropower storage (PHS), also known as pumped-storage hydropower (PSH)
and pumped hydropower energy storage (PHES), is a source-driven plant to store electricity,
mainly with the aim of load balancing. During off-peak periods and times of high
production at renewable power plants, low-cost electricity is consumed to pump water
to a high elevation reservoir. In this way, the surplus electrical power is stored in the form
of gravitational potential energy. When electricity demand increases, the stored water is
released to drive the employed hydraulic turbine(s) of the system and actuate a coupled
electricity generator to produce power. The outlet flow from the higher reservoir can be
controlled to provide variable output power. The roundtrip efficiency of a PHS plant can
reach up to 85%, which is the highest percentage among mechanical energy storage
(MES) technologies. Also, the capacity of such plants can be extremely large, up to a few
thousand megawatts. The main disadvantages of PHS systems are the limitations in
water availability and topography challenges as well as high capital cost. Further, appropriate
sites for this technology seem to be available in the natural environment and
therefore there are also ecological and social concerns to overcome. Even considering
these challenges and drawbacks, PHS is by far the most widely implemented energy
storage technology in the world due to the previously mentioned advantages and
its considerable economic benefits via facilitating the supply of cheap electricity at
expensive times and spot prices and high efficiency. This chapter gives information
about the fundamentals of PHS systems, a history of different kinds of PHS systems,
and the state of the art of the technology. Then, it presents the basic mathematical
model required for analyzing a PHS facility followed by a discussion on the future perspectives
of this technology.