Pumped-storage hydroelectricity
Introduction
Pumped-storage hydroelectricity is a type of hydroelectric energy storage used in the electric power system for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power.
Principle of Operation
The fundamental principle of pumped-storage hydroelectricity is the use of gravitational potential energy. The system consists of two water reservoirs at different heights. During periods of low electricity demand, excess generation capacity is used to pump water from the lower reservoir to the upper reservoir. When there is higher demand for electricity, water is released back into the lower reservoir through a turbine, generating electricity.
Components of a Pumped-Storage Plant
A pumped-storage plant includes the following main components:
- Upper reservoir: This is where the water is stored when it is pumped from the lower reservoir.
- Lower reservoir: This is the source of water that gets pumped to the upper reservoir.
- Waterways: These are the tunnels or pipes that transport water between the two reservoirs.
- Powerhouse: This houses the turbines and generators that convert the energy of falling water into electrical energy.
- Pump-turbines: These machines act as a pump to transport water to the upper reservoir and as a turbine to generate electricity when the water is released back.
Types of Pumped-Storage Plants
There are three main types of pumped-storage plants:
- Pure pumped-storage plants: These plants use only water that has been previously pumped to the upper reservoir.
- Pumped-storage plants with natural inflow: These plants also use natural water inflow in the upper reservoir.
- Mixed plants: These plants use both pumped water and natural inflow for power generation.
Efficiency and Costs
The round-trip energy efficiency of a pumped-storage system is typically about 70-85%, depending on the specific design of the plant and the time-frame of operation. The main cost of a pumped-storage plant is the initial investment for construction, which can be high due to the need for significant civil engineering works. However, the operating costs are relatively low and the lifespan of a pumped-storage plant can be several decades, making it a cost-effective solution in the long term.
Environmental Impact
While pumped-storage plants are generally considered to be a clean source of energy, they do have some environmental impact. The construction of the reservoirs can lead to habitat destruction and the displacement of local communities. The operation of the plant can also cause changes in local water levels and flow patterns, which can affect aquatic ecosystems. However, these impacts can be mitigated through careful site selection and design.
Future of Pumped-Storage Hydroelectricity
With the increasing integration of intermittent renewable energy sources such as wind and solar into the power grid, the demand for energy storage solutions like pumped-storage hydroelectricity is expected to increase. Advanced technologies such as variable speed pump-turbines and ternary units are being developed to increase the efficiency and flexibility of pumped-storage plants.