IEEE Power & Energy Magazine - September/October 2020 - 51

The breakthrough of ac allowed power to be
transmitted longer distances at higher voltages
and ushered in early installations of ac hydropower.
energy relative to a hydro turbine generator. At a lower elevation and together with the ever-reliable force of gravity as a
prime mover, water will flow to a lower elevation, converting potential energy into rotating mechanical torque that
drives a synchronous generator and delivers three-phase ac
to the grid. The fact that gravity is available at no cost and is
not subject to inflation is an additional positive characteristic.

Early Pumped Storage in Europe
By the 1880s, engineers in Europe had designed and built
plants based on mechanical energy storage. An early example was the use of wind power to pump water to an upper
reservoir for later use to drive a waterwheel that powered
belt-driven lathes and similar machines.
There were plants in Europe based on water storage that
would be precursors to hydro storage with pumps, turbines,
and separate motors and generators; two examples are
✔ a plant with a reciprocating pump in Zurich, Switzerland (1882)
✔ a 50-kW centrifugal pump in Luino, Italy, used to
drive a spinning mill (1894).
By the time the first pumped storage project (Rocky Mountain in Connecticut) was built in the United States in 1928,
more than 40 pumped storage hydroelectric facilities had
been built in Europe. The first pumped storage facility in the
world is reported to have been built in 1909 near Schaffhausen, Switzerland. This 1,500-kW pumped storage plant used
a separate pump and turbine.
Other early pumped storage plants constructed in Germany, Switzerland, France, and Italy include
✔ a two-unit plant with 20-MW pumps and 22.4-MW
turbines, Niederwartha, near Dresden, Germany (1928)
✔ four units with 32 MW of total capacity, Schluchsee
scheme in Germany (1928)
✔ the Häusern pumped storage power station, which is
the oldest of the five pumped storage plants in the
Schluchseewerk region (1931)
✔ the Lac Noir Plant (four 20-MW units), the first
pumped storage plant in France (1933).
The usual configuration in these plants was a separate pump
and turbine, each connected by a horizontal shaft to a separate motor and generator. As plants with larger capacity
were constructed, vertical arrangements were introduced.
The vertical shaft configuration was made possible by the
development of bearings that can support the weight of the
motor/generator, shaft, and pump/turbine. See Barnett in the
"For Further Reading" section for a discussion of the use
september/october 2020

of a vertical shaft configuration at the Niagara Falls hydro
generation plant.

The Rocky River Pumped Storage Plant
The Connecticut Light Power Company (CL&P) pioneered
the use of pumped storage in the United States at the Rocky
River hydroelectric station. This project, completed in 1928,
is the first pumped storage station in the United States.
Today, the station serves as the centralized dispatch center
for the CL&P system.
At a meeting of the Connecticut Society of Civil Engineering in 1928, Chief Engineer Paul Heslop started his presentation about the Rocky River pumped storage plant with
the following introduction: "The statement that a hydroelectric plant can pump its own water supply sounds absurd on
the face of it, yet this is virtually what happens in the case of
the Rocky River Hydro Plant." Until then, most residents of
western Connecticut knew the 11-mi-long Candlewood Lake
as a recreational resource for boating, fishing, and swimming. Few people are aware that the lake is part of the first
major project in the United States designed to generate electricity from water pumped into a reservoir.
The project's design was made possible by the economics
of the electricity market, where the power provided during
periods of greatest demand generates the highest rates. To
create Candlewood Lake, builders dammed a pair of tributaries to the Housatonic River, forming the basis for the
reservoir. The 8-mi2 storage area is then filled by pumping
water from the Housatonic at periods when the electricity
to run the pumps is least expensive. The power generated
by releasing the same water can then be sold at higher rates
during periods of peak demand.
The American Society of Mechanical Engineers (ASME)
has included the Rocky River Hydroelectric Plant as project
56 in its list of dedicated mechanical engineering landmark
projects. The following ASME description summarizes the
Rocky River pumped storage project advancements:
Water is pumped uphill through a penstock and stored
in Lake Candlewood. When demand reaches a peak,
water is released through the same penstock, driving
generators to produce electricity. The original penstock, built in 1927, was restored in 1963. Inside the
station electricity is generated by a 38,430-horsepower
vertical shaft Francis reaction type turbine connected
directly to the generator. The station's two original
pumps were 8,100-horsepower each, 54 inches, vertical shaft, single inlet, single-stage centrifugal volute
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IEEE Power & Energy Magazine - September/October 2020

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