Pumped storage power plants in electrical power system is employed mainly to deliver electrical power to the grid during peak demands and support the stability of the grid. These plants are employed where the quantity of water available for power generation is not suitable in a natural manner.
Pumped storage plant consists of essentially head water pond and tail water pond. During off-peak period of the electrical grid, the water from the tail water pond is pumped back to the head water pond or reservoir.
With surplus available energy during off-peak periods, the water is pumped back and stored in the form of hydraulic potential energy by lifting the water from lower level to higher level. . The same stored hydraulic energy is used during peak loads to generate electrical power like conventional power plant. The turbine used for generating electrical power during normal operation is used as pump to pump back the water during low load conditions. Some of the advantages and disadvantages of pumped storage power plants are given below:
Advantages of Pumped Storage Power Plants:
- The complementary nature of the pumped storage plant to the thermal plant and the possibilities of using storage sites which would not be economical for hydro-power alone, have made pumped storage schemes attractive to power utilities.
- By adopting pump-storage plant in conjunction with the thermal power plant reduces the capacity of the thermal power plant (which is used as base load plant) and allowed the thermal power plant to operate at almost 100% load factor. It also reduces the start and stop time of the thermal power plant. This method is more economical than conventional plants particularly when an incremental cost of hydroelectric plant is comparatively low and cost of fuel in thermal plant is high.
- Pumped storage plants are unique among all the hydroelectric power plants as no flowing water supply is required. Once the head or trail pond is filled, then only inflow required is to compensate for the evaporation and separate losses
- Pumped storage plant has one more notable advantage over conventional hydro-electric installations. In the latter type, when the reservoir level goes down too low, the power generation is interrupted. Whereas in pumped storage plants have advantage of producing electrical power by off-load peak pumping water to the reservoir.
- The cost of electricity per unit during high demand (peak load demand) is much more costly than that of during off-peak demands. Thus pumped storage plants have the advantages of generating electricity at lower cost compared to other peak load plants (gas and diesel power plants). Water is pumped back to the reservoir during off-peak loads (eg: during night times). Therefore the cost required to pump back is cheaper.
- By seasonal storage through pumping, the stream flow in other rivers could be used which could otherwise run to waste. This the major advantage of pumped storage power plant.
- Pumped storage plant capacity is not limited by the river flow and seasonal variations in the flow. This is the advantage of pumped storage plants which can be operated all over the year in all seasons.
- In a combination of thermal power plant or nuclear power plant as base load plants and pumped storage plants as peak load plants which are constructed to the closer proximity, pumped storage plant can act as reservoir for cooling the thermal units. In addition to this, the proximity of these plants not only valuable because of reduction in the cost of cooling towers for steam power plant as pumped storage plants acts as reservoir, but also it transfer the power to the pumped storage plants during off-peak conditions.The short transmission lines required will keep the losses to a minimum.
- As with conventional hydroelectric units, pumped storage plants have the advantage of much lower forced-outage rate than the steam generating units. The average plant availability will be of the order of about 95%
- The reserves of thermal power plants consume appreciable amount of energy for keeping the boiler warm. Whereas the pumped storage plants does not require any additional energy to keep the plant in ready for service. Because of the availability for these plants to pick up the loads instantly, pumped storage plants are used emergency reserve stations or peak load stations in the electrical grid system. For shifting from no load to full load, a thermal station needs nearly 30 to 60 minutes whereas the hydroelectric stations require 20 to 60 seconds for operation. Therefore machines of the pumped storage plants are used for regulating purposes. This is the advantage of pumped storage plant.
Disadvantages of Pumped Storage Plants:
- These plants suffers from economical disadvantage as they require a dual conversion of energy is required.