Rezachek & Associates'
Energy & Environmental Resources

HYDROPOWER

HYDROPOWER - What Is It?

Hydropower harnesses the energy in moving water to produce electricity or operate machinery. The force of falling water or flowing streams spins a turbine. The turbine then turns a generator which produces electricity. An older use of hydropower is non-electric power generation. The spinning shaft was attached to a millstone or other machinery rather than to an electrical turbine generator.

Advantages

Hydropower is a renewable energy source. Natural cycles of evaporation and rainfall provide a renewable supply of water. Dams can be built to store water from rivers and streams to assure a continuous supply of water during periods of little rain or diminished stream flow. However, most of Hawaii's hydropower plants operate on "run of the river" flows which do not have dams.
Hydropower plants are economical. The water used is free in most cases. Hydropower plants are long-lasting and usually cost less to maintain and operate than other generating plants. They can often be operated with automatic controls and by remote control from isolated locations.
Hydropower is a proven technology and has been used to generate electricity for more than 100 years. Hydropower plants have contributed power for sugar mills and utilities in Hawaii for many decades. They continue to produce significant amounts of the electricity on the Islands of Kauai, Maui, and Hawaii.
Water going through a hydropower plant is not altered in any way and is available for agricultural and recreational use after it is used to generate electricity.
Use of hydropower as a source of electricity will help reduce the state's dependence on imported fossil fuels.
Reservoirs in hydropower systems assist in flood control by providing storage for water from above-normal stream flow.

Disadvantages

Hydropower depends upon a reliable, year-round flow of water to produce electricity. Hawaiian streams have flows which vary considerably according to seasonal rainfall. Therefore, hydropower in Hawaii is considered an "intermittent" resource.
Many large hydropower projects require damming a river or stream to provide a reservoir of water for use when stream flow is low. This can flood environmentally sensitive areas and/or historic sites.
Dam or stream diversion for hydropower may disturb stream flow by reducing the amount of water flowing downstream. This can damage plants and animals that live in the stream.
Streams are often in remote, previously undisturbed areas, and unless measures are taken to protect or replant those areas, damage from construction can occur.

The Basic Process

In the simplest form of hydropower, flowing water turns a turbine which then turns a generator which produces electricity. The available power depends on the amount of water flowing, and also the pressure, or "head," of the water. Head can be increased by building dams or selecting sites with steep terrain. Pumped storage hydropower plants pump water back up from a lower reservoir to an upper reservoir where it is stored and then released when needed to provide power. This is mostly used for short periods to meet peak power demands.

Use of Hydropower in Hawaii

Hawaii has many hydropower plants located on the Islands of Hawaii, Kauai, and Maui. Although they are small in comparison to many Mainland facilities, they have furnished power to sugar mills and the three island utility companies for many years.

Seven hydropower plants, ranging in size from 0.5-3.8 MW capacity, are located on Kauai. They are operated by Kekaha Sugar Company, Lihue Plantation Company, McBryde Sugar Company, and Olokele Sugar Company. They furnish power for sugar plantation and mill operations. Surplus electricity is sold to the Citizens Utilities Company, Kauai Electric Division. In 1993 these hydropower plants supplied 4.6 percent of Kauai's electricity needs.

Three hydropower plants are operated by Hawaiian Commercial & Sugar Company and one by Pioneer Mill on Maui. The largest has a capacity of 1.5 MW and is located on the Wailoa Ditch. During 1993 these plants furnished approximately 2.0 percent of Maui's electrical needs.

Nine hydropower plants are located on the Island of Hawaii, five of which are located on the Wailuku River near Hilo. Four of these are owned and operated by the Hawaii Electric Light Company (HELCO) and range in size from 0.4-1.5 MW capacity. The fifth hydropower plant located on the Wailuku River is the 12-MW facility operated by Wailuku River Hydroelectric Power Company. The other plants on the island are operated by Hawi Agriculture and Energy Company, the Hamakua Sugar Company, the County Department of Water Supply, and Wenko Energy Company. They supply power for their own operations and can also provide electricity to HELCO. Hydropower plants provided 3.6 percent of the Island of Hawaii's electrical needs in 1993.

The Wailuku River Hydroelectric Power Company plant is the largest in the state and began producing electricity in May 1993. It generates about 34 million kWh of electrical energy annually, enough to supply 5,000 homes and replace 55,000 barrels of imported oil. The plant, which took five years and $30 million to plan and build, is located on state conservation land about five miles from Hilo. A diversion channel was dug to feed three miles of five-foot diameter pipe (penstock) with rushing water for the plant's two turbines.

More hydropower plants on Hawaii, Kauai, and Maui have been proposed but have not completed the permitting requirements.

More recently, Hawaiian Electric Company, in cooperation with the Hawaii State Department of Business, Economic Development, and Tourism and the state Department of Land and Natural Resources, has undertaken a preliminary study to determine the feasibility of installing a pumped storage hydroelectric power plant on the Island of Oahu. Two prospective sites being evaluated are Koko Head Crater, using sea water, and Kaau Crater in Palolo Valley, using water from a Maunawili Valley reservoir.

Most of information contained in this summary was excerpted from a Fact Sheet prepared by the staff of the Energy Division of the State of Hawaii-Department of Business, Economic Development, and Tourism (DBEDT) and published with funding from the U.S. Department of Energy, Grant No. DE-FG49-94R900023. This information does not necessarily reflect the views of the State of Hawaii, the United States Government, or any agency thereof.