Hydropower and Pumped Storage

Hydro is nowadays a mature technology and has been developed  all around the world. In countries blessed with large rivers, hydro plays a major role in the generation of electrical energy.

The most common type of hydroelectric power plant uses a dam to store river water in a reservoir. The water released from the reservoir flows via a penstock (a closed conduit that channels the flow of water) through a turbine driving a synchronous generator to produce electricity. A diversion type hydro power plant (also named a run-of-river facility) does not make use of a dam and channels a portion the river water through a channel and a penstock to use the natural decline of the river bed elevation to produce electricity. A third type of hydro power is called pumped storage hydo power and works as a giant battery. A pumped storage hydro power facility is able to store large amounts of electricity from other power sources for later use. A pump storage scheme has two reservoirs at different heights, with the hydro plant situated at the level of the lower reservoir. During periods of low demand, usually at night, water is pumped from the lower to the higher reservoir using the cheap electricity from the thermal power plants. The generators act as motors and drive the turbines that act as pumps. During periods of peak demand, usually in daytime, the water turbine drives the generator in the normal manner. The overall efficiency of the operation is not very high, between 70-80%. In Europe 170 pumped storage plants with a total capacity of 45 GW are in operation. One of the larger pump storage plants in Europe is located in Vianden in Luxembourg. China has 34 pumped storage plants with a total capacity of 32 GW, Japan has 38 pumped storage plants in operation with a total capacity of 23 GW and the United States 43 plants with an estimated storage capacity of 553 gigawatt-hours.

The Itaipú hydroelectric power plant in Brazil is the world’s second largest hydroelectric power plant with a generating capacity of 14000 MW. It is located on the border between Brazil and Paraguay. The Itaipú dam and power plant are on the Paraná river. The construction of the dam began in 1971 and electricity was generated since 1984. Twenty generators are installed, ten generate 50 Hz for Paraguay and ten generate 60 Hz for Brazil. The output of the Paraguayan generators can be exported to the Sāo Paulo/ Rio de Janeiro region by means of two 800 – kilometer - long 600 kV HVDC transmission lines. The Three Gorges dam in the Yangtze river (185 meters tall and 2309 meters wide) was completed in 2008. In 2012 all 32 hydro units were commissioned to generate a total of 22,500 MW output.

The abundant hydropower resources in southwest China will be exploited on a large scale during the next decades. A number of large hydropower projects will be completed during this period. China ranks first in the world of hydro resources with a potential of 680 GW. An estimated 370 GW can be developed to provide electric energy production of 1900 TWh/year. Exploitable hydropower resources in southwestern China account for 53% of China’s total.

The United States is the 3rd largest producer of hydroelectric power in the world in 2021 after Brazil and China. Total installed capacity for 2020 was, according to the International Hydropower Association, 102,8 GW. The Hoover Dam in the Colorado river on the border of Arizona and Nevada was constructed between 1931 and 1936. The maximum capacity is 2000 MW, but the severe drought in the western United States has decreased how much power it can produce. In June 2023 it was roughly 1000 MW.

Canada ranks four on the list of producers of hydro power. Manitoba Hydro for instance has a total generating capacity of 6100 MW.

Thanks to its natural geography Norway is well suited for hydro power use. Norway currently possesses approximately half of Europe’s entire storage capacity and is in the position to provide large-scale, cost-effective and emission-free indirect storage to balance the production of wind- and solar-energy of other European countries.

Tidal power is a form of hydropower that converts the energy of tides into electricity. This way of producing electricity suffers from high costs and a limited availability of sites with sufficiently high tidal ranges or flow velocities. The two largest tidal power stations are the Shiwa Lake tidal plant (254 MW) in South Korea and the French Rance tidal power plant (240 MW).

The running costs of hydropower plants are rather low as energy is free, but the civil engineering component of the capital cost is very high. The type of water turbine used depends on the head of water available. The energy is extracted from the water falling through the available head. The lower the head, the larger the quantity of water necessary for a given turbine rating. High-head turbines operate with low water volumes and low-head turbines with high water volumes.

There are three basic types of water turbines. The Kaplan turbine has variable pitch blades that can be adjusted for optimum regulation. This type of turbine has been built for heads up to 60 m and is applied in river and pondage stations.

In the Francis turbine the guide and runner blades are designed for higher heads up to 500 m, and the regulation is done by adjustment of the guide vanes at the water inlet.

The third type is the Pelton wheel, a turbine suitable for high heads and small quantities of water. The water is injected through one or more nozzles on the buckets on the turbine wheel. The regulation is done by means of needle valves on the nozzles and jet deflectors at the water inlet.

In comparison with a thermal power plant, a hydropower plant has the advantage of quick starting and effectively meeting an abrupt increase in load demand. When water supplies are not available, a pump storage scheme provides the advantages of a hydro plant.