Robert Moses Niagara Hydroelectric Power Station - Lewiston Pump-Generating Plant

Lewiston Pump-Generating Plant

The facility is not a typical dam, in that it was constructed not to control the flow of water in a natural river, but rather to contain a man-made 1,900-acre (7.7 km2), 22-billion-US-gallon (83,000,000 m3) upper reservoir which stores the water for day-time use through a tunnel from a point upstream on the Niagara River. The opposite boundary of this forebay is another dam. This dam is part of the 240-MW Lewiston Pump-Generating Plant 43°08′33″N 79°01′18″W / 43.14250°N 79.02167°W / 43.14250; -79.02167 (Lewiston Pump-Generating Plant), which houses 12 of electrically powered pumps that can move water to another higher storage reservoir behind this second dam.

At night, a substantial fraction (600,000 US gallons (2,300 m3) per second) of the water in the Niagara River is diverted to the lower reservoir by two 700 ft (210 m). tunnels. Electricity generated in the Moses plant is used to power the pumps to push water into the reservoir behind the Lewiston Dam. The water is pumped at night because the demand for electricity is much lower than during the day. In addition to the lower demand for electricity at night, less water can be diverted from the river during the day because of the desire to preserve the appearance of the falls. This prevents the plant from withdrawing such a large amount water during other times of low demand, such as weekends. During the following day, when electrical demand is high, water is released from the upper reservoir through generators in the Lewiston Dam. That same water flows into the lower reservoir, where it falls again through the turbines of the Moses plant. Some would say that the water is "used twice." This arrangement is called pumped-storage hydroelectricity.

This system allows energy to be stored in vast quantities. At night, the potential energy in the diverted water is converted into electrical energy in the Moses plant. Some of that electrical energy is used to create potential energy when the water is pumped into the reservoir behind the Lewiston Dam. During the day, part of the potential energy of the water in the Lewiston reservoir is converted into electricity at the Lewiston Dam, and then its remaining potential energy is captured by the Moses Dam, which is also capturing the potential energy of the water diverted from the river in real-time.

Beginning in 2012 and continuing through 2020, the pump-generating plant will be undergoing a $460 million modernization that will increase the plant's efficiency and service life. Previously, a refurbishment of the Robert Moses Plant was completed in 2006.