In the utilization of hydropower resources, not only can power generation be generated through the construction of hydropower stations, but also the potential energy of electric energy can be converted into water and stored through the construction of pumped-storage power stations, so as to achieve the effect of “shaving peaks and filling valleys”. Pumped storage power stations have been widely used abroad for many years, and China has also begun to vigorously build them.
- Composition and principle of pumped storage power station
Pumped storage power generation is another form of water energy utilization. It does not develop water resources to provide electricity to the power system, but uses water as a medium for energy storage and release. When there is surplus electricity, energy is stored, and when electricity is insufficient The energy is released to redistribute and regulate the power supply of the grid.
Pumped-storage power stations generally use reversible turbines that have both pump and turbine working modes. There are two working conditions for the reversible hydro-generator set: when the power load is at a low point (at night), the reversible hydro-turbine operates as a water pump, and the generator operates as a motor. The water pump pumps the water from the lower reservoir to the upper reservoir for storage, which is called forward pumping; when the power load peaks, the water from the upper reservoir is released, and the reversible turbine operates as a turbine to drive the generator to generate electricity, said for reverse power generation.
Although the process of pumped storage and discharge of water to generate electricity is reversible, energy will be lost. The ratio of hydroelectric power generation to pumping power consumption is about 75%, that is, when the water from the lower reservoir is pumped to the upper reservoir with 1kW·h of electric energy, and then the water from the upper reservoir is released for power generation, the power generation is caused by various losses. The amount is only 0.7kW·h at most. However, since the ratio of the on-grid electricity price at the peak (peak) moment of electricity consumption and the moment of electricity trough (valley electricity) is greater than 1, which is generally 4:1 in foreign countries, there is still huge profit space for the construction of pumped storage power stations.
The hydraulic structures of the pumped-storage power station are mainly composed of an upstream reservoir (upper reservoir), a downstream reservoir (lower reservoir), a water diversion system (high pressure part), a low pressure part of the water diversion system), and power plant buildings. The basic structure of the pumped-storage power station is shown in Figure 1.
Pumped storage units can be installed in a power station with conventional hydropower units. Such a power station has both grid regulation and runoff power generation functions, which is called a combined constant storage or hybrid power station. Some energy storage power stations are specially built for grid regulation, which are called pure pumped storage power stations.
The development methods of pumped-storage power stations can be roughly divided into three types: (1) pure pumped-storage power stations; (2) pumped-storage power stations combined with riverbed hydropower stations; and (3) pumped-storage power stations combined with barrage-type hydropower stations.
Pure energy storage power stations tend to use high water heads, because under the same capacity and energy storage conditions, the higher the effective water head, the smaller the required flow and storage capacity, and the lower the unit cost. Therefore, the cost of pumped storage power stations varies with the water head. increase and decrease.
China’s high-head storage power stations, such as Guangzhou Pumped Storage Power Station, Mingling Tombs Pumped Storage Power Station, Tianhuangping Pumped Storage Power Station, etc., have used water heads of 400-600m.
The water head of the energy storage power station using single-stage pump-turbine in foreign countries has been used more than 700m, and the water head of the energy-storage power station using multi-stage pump-turbine has been used up to 1300m.
- Application status of pumped storage power station
The Leighton pumped-storage power station built in Switzerland in 1879 is the first pumped-storage power station in the world. In 1882, Switzerland built the Neitra power station in Zurich with a power of 515kW. It is a seasonal pumped storage power station. Many people think that this is the first pumped storage power station in the world.
In the late 20th century, the world’s pumped-storage power stations developed rapidly, especially from the 1960s to the 1980s was the golden age of rapid development of pumped-storage power stations. The total installed capacity of pumped storage power stations in the world was 1.6 million kW in 1950, 3.42 million kW in 1960, 11.6 million kW in 1970, 46.52 million kW in 1980, and 80.68 million kW in 1990, with an average annual increase every ten years. The rate was 7.89%, 17.14%, 10.8%, and 10.6% in sequence. In 2000, it exceeded 100 million kW.
By the end of the 1980s, some industrially developed countries in the world, such as Switzerland and France, had almost fully exploited the hydropower resources. Later, the economical options for conventional hydropower stations in Japan and other countries have been basically developed, mainly focusing on the construction of pumped storage power stations. By 2010, the total installed capacity of pumped storage power stations in the world has increased to 135 million kW, mainly distributed in Japan, the United States, China, Italy, Spain, Germany, France, etc., and nearly 80% in Europe, the United States, Japan and China.
China also attaches great importance to the development of pumped storage power stations. In addition to conventional hydropower stations, the construction of pumped storage power stations in China has also made great achievements. Since the 1970s, regional power grid systems dominated by green power have required the development of new pumped storage power stations (such as using new renewable clean energy to directly drive pumped power units as new storage pumps) to improve energy efficiency. Pumped-storage power stations are mainly built in areas with less water resources to meet the needs of power system peak regulation.
In the 1990s, China’s pumped-storage power plants entered a stage of large-scale development. By the end of 2013, China had built 21.51 million kW of pumped-storage power stations, the unit utilization hours were 1281.9 hours, and the equivalent availability factor was 97.41%. Among the pumped storage units that have been put into operation, the unit capacity of Tianhuangping and Guangzhou pumped storage power station is 300,000 kW, which has reached the world advanced level of single-stage reversible pump-turbine. Nevertheless, given the low proportion of gas-fired units available for peak shaving in China, the capacity of pumped storage units is still only 1.76% of the total installed capacity, much less than that of the United States, Japan and the European Union.
Recently, the pumped storage units under construction in China are about 8.9 million kW, and the capacity of pre-feasibility research projects is over 30 million kW. On May 29, 2013, Hebei Fengning Pumped-storage Power Station, a key project of the National Energy Development “Twelfth Five-Year Plan” plan and construction, started construction. After the project is completed, it will become the world’s largest pumped-storage power station with installed capacity.
Best in China: China’s largest pumped-storage power station
Guangzhou Pumped Storage Power Station (Figure 2) is a supporting project of Daya Bay Nuclear Power Station. It is built to ensure the safe and economical operation of Daya Bay Power Station and meet the needs of Guangdong Power Grid for valley filling and peak regulation. The area of the power station is 27km2, the water area of the upper and lower reservoirs is 7.4 million m2, and the accumulated rain area is 19.4 million m2. The altitude of the upper reservoir is 900m, the lower reservoir is 270m, and the drop is 630m.
With a total installed capacity of 2.4 million kW, the power station is currently the largest pumped-storage power station in China. The power station is constructed in two phases, with a total installed capacity of 8 units. It adopts a 300,000 kW reversible high-parameter pumped storage unit with a design head of 535m, a rated speed of 500r/min, and a comprehensive efficiency of 76%.
The world’s highest: the world’s highest pumped-storage power station in Shanghai
Yamdrok Lake Pumped Storage Power Station is located in Gonggar County, Tibet Autonomous Region, China. It is a hybrid pumped storage power station. The ground height of the power station plant is about 3600m, which is the highest pumped storage power station in the world and the pumped storage power station with the highest water head in China. Electricity The Yangzhuoyong Lake (Yamdrok Yongcuo) is used as the upper pool, and the Brahmaputra River is used as the lower pool. The water level difference of 840m and the horizontal distance of about 900m between the Yarlung Zangbo River and the Yarlung Zangbo River are used to build water diversion structures to generate electricity, with a total installed capacity of 11.25 million kW (5 × 22,500 kW), and another 22,500 kW conventional unit is reserved.
According to the “Notice on Issues Concerning Improving the Price Formation Mechanism of Pumped-storage Power Stations” issued by the National Development and Reform Commission, China will regard pumped-storage power stations as an important means to optimize the energy structure, promote the development and utilization of new energy and protect the ecological environment. By 2025, the total installed capacity of pumped-storage power stations in the country will reach about 100 million kW, accounting for about 4% of the total installed power capacity in the country.
The pumped-storage power stations that have been built in China mainly include Guangzhou pumped-storage power station, Zhejiang Tianhuangping pumped-storage power station, Beijing Shisanling pumped-storage power station, Hebei Panjiakou hybrid pumped-storage power station, and Tibet Yangzhuoyong Lake. Pumped storage power station, etc.