The Power of Water

Ever switch on power it has, this is usually depend- a light and ent on the size of the dam); and THE BASIC wonder the amount of water falling (more COMPONENTS OF where the water falling through the turbine will A CONVENTIONAL electricity produce more power, the amount HYDROPOWER UNIT came of water available depends on the from? amount of water flowing in the river). Dam: Most hydropower plants rely It might on a dam that holds back water, have While hydropower stations are con- creating a large reservoir. just been sidered more environment-friendly Intake: Gates on the dam open generated than coal-fired stations, there is some and gravity pulls the water through by the power debate whether they should really the penstock, a pipeline that leads of water. be actively pursued. This is because to the turbine. Water builds up pres- most hydropower stations involve the sure as it flows through this pipe. Water can be used construction of a dam, which can be Turbine: The water strikes and in two ways to disruptive to the surrounding environ- turns the large blades of a turbine, generate electricity. ment and to communities who might which is attached to a generator Conventional hydro- be displaced. above it by way of a shaft. electric stations Generators: As the turbine blades capture the energy of Because of its limited water turn, so do a series of magnets falling water to gener- resources and erratic rainfall, South inside the generator. Giant magnets ate electricity. A turbine Africa does not have much poten- rotate past copper coils, producing converts the kinetic tial for large hydropower stations. alternating current (AC) by moving energy of falling water Whereas, worldwide, about 20% electrons. (usually from a dam) of all electricity is generated by Transformer: The transformer into mechanical energy. hydropower, in it varies inside the powerhouse takes the Then a generator converts between 2% and 4%. The country’s AC and converts it to higher-voltage the mechanical energy from the largest power producer, , current. turbine into electrical energy. The operates six hydropower schemes at Outflow: Used water is carried electricity generated is fed on to the present. through pipelines, called tailraces, transmission lines that link up with the and re-enters the river downstream. national electricity grid. Once the water There are two hydropower stations has run through the turbines it is dis- on the . The Gariep Source: www.howstuffworks.com charged back into the river below the to continue its course.

On the other hand, pumped storage schemes reuse water to generate power. The schemes use off-peak energy to pump water into an elevated dam from a lower dam from which it can be released to generate electric- ity when required. When the energy is needed, the water is released from the top dam to flow through the power station to the bottom dam.

The amount of electricity a hydro- power plant produces depends mainly on how far the water falls (i.e. The forms part of the Palmiet Pumped Storage Scheme, the further the water falls, the more in the Western Cape.

The Water Wheel January/February 2007 (formerly known as Hendrik Verwoerd) hydropower station started feeding into Eskom’s transmission system in 1971. Vanderkloof, a similar hydro- power station, was commissioned in 1977.

Eskom also operates four smaller hydropower stations, namely Colley Wobbles (Mbashe River), First Falls and Second Falls (Umtata River), and Ncora (Ncora River). The (particularly the area of the former Transkei) and parts of KwaZulu-Natal have been identified as having the most potential for the The is also used for hydropower. future development of hydropower in South Africa. There are also a number of independ- HYDROELECTRIC FIRSTS ently-operated hydropower stations in IN SOUTH AFRICA In addition, there are two pumped South Africa, for example, the 2,5 MW storage schemes at present. The Friedenheim mini-hydropower plant • The first hydropower plant on the Drakensberg Pumped Storage situated on the Crocodile River, near Orange River was constructed Scheme not only supplies the country Nelspruit, Mpumalanga. This plant near Kakamas, in the Northern with 1 000 MW of electricity during has been operational since 1998 to Cape. peak periods, it also assists in sup- provide power for the Friedenheim • The Sabie River Gorge power plementing the Vaal Dam with water Irrigation Board while excess power is station was the first hydropower transferred from the Tugela River in sold to Mbombela Municipality. station to be erected by Eskom. KwaZulu-Natal. Completed in 1988, It started commercial operations the 400 MW Palmiet Pumped Storage The Bethlehem Hydropower Project in 1927, and was built mainly to Scheme is situated about 50 km from is currently under construction. The support mines in the area. The . This scheme is also used project comprises two generation plant closed in 1964. to pump water from the Palmiet River facilities: a 2,2 MW run-of-river site • The hydroelectric power station catchment into the Steenbras Dam located on the As River, midway at the was the to supplement Cape Town’s water between Bethlehem and Clarens; first power station in South Africa supply. At present, Eskom is also and a 1,7 MW facility at the exist- situated entirely underground. developing a third pumped storage ing concrete wall of the Saulspoort • The Friedenheim Hydro Power scheme at Braamhoek, in the Klein Dam, in Bethlehem. The first elec- plant is recognised as the first Drakensberg (for more details, see tricity is expected to be delivered independent power producer in the article elsewhere in this issue). later this year. South Africa. HYDRO-ELECTRIC WEBSITES TABLE 1 Eskom’s hydropower & pumped storage schemes • http://www.dme.gov.za/energy/ Hydroelectric Stations Area Total Capacity renew_hydro.stm Colley Wobbles Mbashe River 42 MW • http://assets.panda.org/down- First Falls Umtata River 6 MW loads/africahydropowerre- Gariep Orange River 360 MW port2006.pdf Ncora Ncora River 2 MW • www.eskom.co.za Second Falls Umtata 11 MW • http://mp2mas26.eskom.co.za/ Vanderkloof Orange River 240 MW heritage/main.htm Pumped Storage • http://people.howstuffworks. Drakensberg Bergville, KZN 1 000 MW com/hydropower-plant.htm Palmiet Grabouw, Western Cape 400 MW Source: Eskom

The Water Wheel January/February 2007