In the context of Nepal, the Integrated Nepal Power System (INPS) is predominantly a hydro-dominated one, where the base and intermediate power demands are met by run-of-river hydropower plants and import from India. Therefore, the national grid should have storage power plants to improve system reliability..
A method of storing electricity is necessary so that it can be generated at one time and used at another, when necessary. Electricity itself cannot be stored, but it can be converted into other forms of energy and stored as chemicals or gravitational potential energy and then be converted back to electricity when needed..
One method that can be tried is pumped storage. The principle of pumped storage is fairly simple – utilising gravitational potential to store energy. Two reservoirs, one more elevated than the other, and a system of tunnels and pipes connecting them are needed. When demand is low and electricity is cheap the plant uses energy to pump water from the lower reservoir to the upper reservoir. When demand is high and electricity is more expensive water from the upper reservoir is released back into the lower reservoir through the same system of pipes or tunnels, this time the turbines acting as they would in a traditional hydroelectric plant generating electricity. This type of plant once operational can quickly respond to energy demands. The efficiency of this system is typically between 70 per cent and 85 per cent, making it one of the more efficient methods for storing energy. Pumped storage plant can also be used as solar energy storage..
The Department of Electricity Development (DoED) has planned to develop Sunkoshi-II (1,110 MW) and Sunkoshi-III (536 MW) projects as pumped-storage projects for the first time in Nepal. As per the plan, water will be pumped from the reservoir of Sunkoshi III, which will remain below the Sunkoshi River, to Sunkoshi III during the off-peak hour and release the stored water during the peak hour..
This modality is expected to help address power demand during winters. Currently, DoED is preparing to carry out a DPR for the projects. The Asian Development Bank (ADB) recently signed a loan agreement with the government to fund the DPR. Officials at the Nepal Electricity Authority (NEA) say the Sunkoshi III project can be completed by 2021 if construction starts immediately after the DPR..
According to Nepal Electricity Authority (NEA) study, the system grid will not generate sufficient peak power, even after the completion of 456 MW hydro-power project. Therefore, NEA is planning for series of storage projects to diversify energy generation. In this connection, NEA has planned for the construction of Rupatal-Begnas Tal pumped storage project in mid-western part of Nepal. According to preliminary survey, the project will generate about 100 to 300 MW of power utilising the natural head of 57 metre that exists between Begnas Tal and Rupa Tal. The project is designed to generate peak power for four hours during peak time..
Due to global warming and subsequent climate change, Nepal needs to urgently identify sites for pumped storage projects. A reasonable number of pumped storage plants will help deliver energy security in the long term, besides enhancing system reliability. Pumped storage projects require significant capital for development. Choosing the right location is a matter of identifying a site with ideal topography, a source of water and good proximity to and location within the transmission network. To repay heavy capital investment, the power purchase price should be over and above the break-even cost of pumping..
In the case of severe drought, the upper reservoirs thus constructed, can be used for drinking water, irrigation, hydropower et cetera..
Pradeep Gangol : The author is a freelance engineer, with interests in energy, environment and economic development. He can be contacted through prdpgl@gmail.com.
Source : The Himalayan Times
