Energy Storage at the Distribution Level – Technologies, Costs and Applications
1.1.1 Pumped Hydro Storage A PHS system works on the principle of electromechanical energy conversion. PHS facilities are large-scale energy storage plants that use gravitational force to generate electricity. Water is pumped to a higher elevation for storage during low-cost energy periods and high-renewable energy-generation periods. When electricity is needed, water is released back to the lower pool, generating power through turbines. A closed-loop PHS operates without being connected to a continuously flowing water source, unlike traditional pumped hydro storage, making pumped hydro storage an option for more locations. Reservoirs, if available naturally, are required to pump water from a low-lying water source during motoring mode to a high-altitude reservoir to store the energy in potential energy at height. The water is then released during the generating mode to run a turbine-generator set to generate electricity to be fed into the bulk-transmission network. In India, the state of West Bengal is amongst the front runners of utilizing PHS in its power network to manage system demand. The geographical location of West Bengal provides the edge to West Bengal State Electricity Distribution Company Limited (WBSEDCL) over other distribution utilities in terms of favorable sites for such storage systems. The Purulia Pumped Storage Project (PPSP) is one of the largest in the country. Based in the Purulia district, it is a-225 MW × 4 system. This project utilizes excess available power in the system during off-peak times to flatten the load curve. The project works in four operational modes: (i) generation, (ii) pumping, (iii) synchronous condenser, and (iv) line-charging (up to 400 kV bus) mode. The generation voltage is 16.5 kV. Figure 3 shows the plant and one of the tunnels.
FIGURE 3: Site images of PPSP in West Bengal4
The major issues associated with such an energy storage technology are the long-gestation period, high-upfront capital required including extensive civil works. It is worth mentioning, the cost of generation, including its storage, is very low, however, the round-trip efficiencies are a bit low.
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https://portald.wbsedcl.in/irj/go/km/docs/documents/WBSEDCL_DOCUMENTS/INTERNET/Website_
28FEB2011/Puruliwa_Pumped_Storage_Project_2.html
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