Tidal Power: Operating Principles, Pros and Cons, Operational Efficiency

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Electrical energy plays an extremely important role not only in people’s daily activities but also in determining the production process of the whole world. Because that is also most clearly seen when looking at the history of the late 19th century when electric energy was introduced into production and business by the French in Vietnam. 

Today, with the outstanding development of science and technology, the electricity industry in general and hydropower in particular are also becoming increasingly diverse. And currently, the term pumped storage hydropower is receiving attention and becoming a “hot” topic when talking about our country’s electricity industry. So what is pumped storage hydropower ? Issues related to pumped storage hydropower will be answered in the article below.

What is pumped storage hydropower?

Pumped storage hydropower is a form of hydroelectric power that stores energy, with the main purpose of accumulating electricity to supplement the system when needed. It is a solution to balance the load to help other power plants operate more efficiently. 

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Pumped storage hydropower was invented as a battery of the electrical system, which can supplement electrical energy at any time when fully stored. This is an extremely urgent solution, especially in the context of today’s electrical energy crisis with no signs of positive changes. At the same time, the goal of Net Zero is coming very close.

Operating principle of pumped storage hydropower

The model of pumped storage hydropower is two water reservoirs at two different elevations and a hydroelectric plant. The hydroelectric plant will have a reversible turbine located near the lower reservoir, connected by penstock to the upper reservoir. The operating principle of pumped storage hydropower is based on balancing the load demand of the power system.

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During peak hours, when electricity demand is high, water is released through a pressure pipe from the reservoir above, turning a turbine to generate electricity to the system, and the discharged water is stored in the reservoir below. 

During off-peak hours, when electricity demand is low, the plant draws power from the system to pump water back from the lower reservoir to the upper reservoir through a two-way turbine, which now operates as a pump. 

Pumped storage hydropower is not only a unit of electricity production, but also a unit of electricity consumption. The practical basis for this operating method is the difference in electricity prices between peak hours and off-peak hours.

Advantages and disadvantages of pumped storage hydropower

The important role of pumped storage hydropower is to generate electricity to cover the peak – fill the bottom of the daily load chart. In fact, pumped storage hydropower will help stabilize the system, reserve the necessary electrical energy when the plant has a power shortage during operation, thereby adjusting the frequency. 

Especially helping to stabilize the power flow during peak hours and in the context of the installed capacity of solar power plants increasing very high.


Pumped storage hydropower is a solution to increase the efficiency of the load system. It has the advantage of making the most of excess electricity from thermal power plants (coal power, gas power, nuclear power…) during off-peak hours. This helps increase stability for other factories.

As a backup tank when electricity demand suddenly increases, power plants will not be overloaded and have a shortage of electricity. This is truly an optimal method of using natural energy sources, which is both timely, safe, and especially environmentally friendly.

In addition, this method does not require much storage, is not affected and depends heavily on the annual hydrological regime.


The main disadvantage of pumped storage hydropower is that its operating efficiency is not high (about 70-85%).

Unlike an independent power plant, pumped storage hydropower is limited in that it can only function as a backup energy tank in a relatively large capacity power system.

To establish a pumped storage hydropower model, it needs to be built on a special terrain, which are areas with large elevation differences but must be close to the water source to arrange two reservoirs. Because of this characteristic, this method also has difficulty in choosing the most suitable terrain location to perform.

5 factors affecting the operating efficiency of pumped storage hydropower

In some cases, pumped storage hydropower is also built based on using the sea and ocean as the reservoir below.

  • Natural conditions: Because pumped storage hydropower plants need to operate on the principle of the difference in height between the upper lake and the lower lake, the conditions for building the upper and lower lakes. Therefore, terrain is an important issue in the choice of construction because it determines their strength as well as their ability to operate. 
  • Location: Pumped storage hydropower is created to help support the plant, so it is necessary to choose a location as close to the electrical load as possible to help minimize transmission costs.
  • Electricity price: The economic efficiency of pumped storage hydropower will be directly affected by the difference in electricity purchase prices at off-peak and peak times. This difference will be extremely proportional to the development of this type of factory. Therefore, this is a big issue that any pumped storage hydropower plant pays special attention to.
  • Technological development: A factory operates efficiently when it has low costs, which is determined by the technology applied to it. The more modern the technology, the more operating costs will be optimized and at the same time improved the quality of the factory.
  • Environmental requirements, ecological protection: The development of pumped storage hydropower is related to the environment. Because the increasing requirements for the ecological environment will improve solutions to exploit clean electricity, bringing high efficiency.

Pumped storage hydropower in Vietnam

Vietnam Electricity Corporation has been researching potential pumped storage hydropower projects under the advice of Japanese experts (JICA). 

The Prime Minister has approved the Bac Ai pumped storage hydropower project in Ninh Thuan province (capacity of 1200MW), which has been officially approved by EVN as a pre-feasibility report (May 2015) and is conducting survey work. Supervision and design (performed by Electric Construction Construction Joint Stock Company 4).

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At the beginning of 2020, the first pumped storage hydropower plant in Vietnam was built in Ninh Thuan province and named Bac Ai pumped storage hydropower plant. The project includes 4 units, with a capacity of 1,200 MW with a total investment of about 21,100 billion VND. 

The lower lake of this project is used from water from Song Cai lake of the Tan My irrigation system. Water is pumped to the upper reservoir to generate electricity through two parallel pipelines with diameters varying from 5.5 to 7.5 m and 2.7 km long. The factory is equipped with many modern equipment such as pumps, reversible turbines and reversible engines and generators. The project is still being implemented and is expected to be completed in 2028.

Bac Ai Pumped Storage Hydropower plays an important role in the national electricity system, with the task of generating electricity to cover the top and bottom of the daily load chart. The project not only helps reserve generation capacity and stabilize the system, but also helps regulate frequency, which is a tool to help regulate the national power system to operate stably, safely and reliably.