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(March 31,2010 Update)

Hydroelectric Power Generation

Hydroelectric power generation, drawing on the force of nature, is a method free of CO2 emissions that takes advantage of one of the few energy sources available right in Japan. It is a power source quickly adaptable to power demand.

How Hydroelectric Power Generation Works

A hydroelectric plant generates electricity by means of a water turbine, driven by the force of water flowing down from a higher elevation. Various types of plants are introduced here, differing in the way they obtain and utilize water.

Hydroelectric Plant Types

Pumped Storage Type

Consisting of a power plant built mostly underground plus upper and lower regulating ponds, this type of facility is used to meet peak daytime demand for electricity. During the daytime, power is generated from water flowing from the upper to lower ponds. The water used for generation is stored in the lower pond.

During overnight off-peak hours, water is pumped from the lower pond back to the upper pond, so it can be used again for power generation during the next daytime peak demand period. In this way a fixed volume of water is used repeatedly.

Run-of-River Type

Power is generated by diverting naturally flowing water from a river. The amount of electricity that can be produced varies between high-water and low-water seasons.

Regulating Pondage Type

A water intake dam is expanded or a regulating reservoir is built along the path of water to the power plant, so that the amount of power generated per day or over several days can be controlled by adjusting the amount of water flowing downwards.

Reservoir Type

A reservoir larger than a regulating pond collects the runoff from snow and heavy rain, for use during dry periods.


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