Hydro renewable energy storage developments
Hydropower energy storage technologies have been applied in many emerging economies and developed countries to optimise hydropower supply and generation to improve fits with market requirements. The traditional hydropower
Hydropower & ocean renewable energy management 67 energy storage approach has been to use reservoirs for balancing variable renewable electricity generation and for managing water supply. Pure hydropower pumped storage plants, involving reservoir schemes, are more of a means to store hydro energy and will normally involve conversion losses. A good example is the pumping of water uphill to a storage reservoir during low-power demand periods, such as during nighttime. The water pumping power could be by renewable or non-renewable generated electricity. Then the water from the reservoir can be released downhill to generate electricity during peak demand periods. Pumped storage hydropower schemes have traditionally played important roles in balancing grid power supplies and in the integration of variable renewable hydropower energy resources. A good example of a hydropower-pumped storage system is the Cruachan Hydropower Station that has been installed and operating in Scotland, UK. The Cruachan Power Station, together with the Cruachan Dam, is a pumped-storage hydroelectric power station located in Argyll and Bute, Scotland. The hydropower scheme can provide 440 MW of clean hydropower electricity and has a capacity of 7.1 GWh.
China has been the global market leader for installed pumped hydropower storage capacities. China’s hydropower development plans have sought to optimise the potential capacities and values of pumped storage in hydropower generation. This has also help to balance China’s overall renewable power supplies with wind power and solar PV generation. Switzerland and Portugal have been following China in the application of pumped hydropower installations globally (REN, 2018).
Hydropower energy storage capacities have long been critical components of the modern hydro renewable energy infrastructure. These hydropower storage systems have helped to support power generation at peak hours and storage at low demand hours. These should then help to improve the overall reliability and efficiency of hydropower renewable systems. Hydropower reservoirs can be designed to passively store energy by reducing outputs during low electricity demand periods. It will normally utilise natural or pumped water flows to raise the water levels and energy potentials in the reservoir, thereby achieving effective energy storage. Conversely, pumped storage can be used to directly absorb surplus power off the grid to pump water to storage. These innovative combinations should then allow the hydropower plant to generate the maximum amount of clean electricity supplies for the grid, at peak demand hours.
The growing penetration of new hydropower variable renewable energy (VRE) schemes has raised interests in additional hydropower electricity storage capacities. Pumped storage hydropower has been the dominant form of large-scale hydropower energy storage schemes traditionally. It has accounted for an estimated 96% of global energy storage capacity. Global hydropower pumped storage capacity has been rising in recent years. New hydropower storage capacity has been installed in China, Portugal and Switzerland.
A good example of a modern hydropower energy storage scheme is located in South China in Shenzhen. China has recently completed the first 300 MW of a 1.2 GW hydropower storage plant in the fast growing Shenzhen city. Thisis China’s first large-scale pumped hydropower storage facility, which has been built within a modern urban environment.
In Europe, three mixed pumped hydropower storage plants have also recently entered service. Each of these has incorporated an open-loop system which would combine pumping capacity with conventional hydropower generation from natural flows. A good example is the Veytaux hydropower plant in Switzerland which was originally built in 1971. In 2017, its capacity was doubled with the addition of two 120 MW generators. The expanded hydropower plant can pump water from Lake Geneva to the Hongrin reservoir which is 880 m higher in altitude with a hydropower generation capacity of 420 MW.
Another good example is Portugal’s 780 MW Frades II and 263 MW Foz Tua pumped storage plants which have both entered service in 2017. The two variable-speed 390 MW pump turbines of Frades II are the largest of their kind in Europe. They can respond faster and better to changing electricity grid demands than conventional turbines with fixed speed controls. In addition, they should be more stable against voltage fluctuations and drops. Many projects in Europe have also been incorporating variable-speed turbines for improved flexibility and for providing wider operating ranges. These should help to accommodate the rising penetration of variable renewable energy (VRE) in Europe and globally.
Climate change and global warming have led to more extreme drought incidents globally, especially in Europe and Africa. A good drought example is the severe drought induced by global warming in Portugal in 2017. This extreme drought incident highlighted the importance of pumped storage and hydropower reservoir system. These systems have helped to provide reliable hydropower energy supplies which contributed to stabilising electricity supplies and prices during emergency situations. In addition, the reservoirs provided supports for stable water supplies during severe drought periods. Subsequently, Portugal has begun to consider interconnecting its various dam infrastructures and increasing the storage capacity of existing dams.
