Pumped Storage Hydropower

Pumped storage hydropower is a way to store electricity using water and two reservoirs at different heights. When there is extra electricity, it pumps water up to the higher reservoir. When electricity is needed, it lets the water flow back down through turbines to make power. It works like a giant, rechargeable battery made of water.

Why is it needed?

Solar power is plentiful at noon but disappears at night. Wind power rises and falls with the weather. But people need electricity in the evening peak, when solar is gone. Without storage, extra solar power at noon is wasted, and the evening needs costly or polluting plants. Pumped storage moves cheap daytime power to the evening. It also helps keep the grid stable.

How does it work?

1. Pumping mode: When power is cheap and extra (for example, sunny afternoons), the plant uses electricity to pump water from the lower reservoir to the upper one.
2. Storage: The water waits in the upper reservoir. Its height holds the stored energy.
3. Generating mode: When demand peaks, water flows down through the same machines, which now act as turbines, and electricity is produced.

The same machine works as a pump in one direction and a turbine in the other. It is called a reversible unit. Some energy is lost in each cycle. About 70 to 80% of the power used for pumping comes back as electricity. This is called round-trip efficiency. For example, India's Tehri pumped storage plant has a round-trip efficiency of about 79%.

Types of pumped storage

• On-river (open-loop): Uses reservoirs on a flowing river, often existing dams.
• Off-river (closed-loop): Two reservoirs built away from a river, filled once and then reused. They affect rivers less and can be built faster (about four years).

India's position and examples

As of 31 December 2025, India had 10 pumped storage projects in operation, with a total of about 7,175.6 MW (about 7.2 GW). Another 10 projects of about 11,620 MW were under construction. Examples:

• Tehri PSP (Uttarakhand): 1,000 MW (4 × 250 MW), built by THDC. It is India's first variable speed pumped storage plant. It uses the Tehri and Koteshwar dams on the Bhagirathi as its upper and lower reservoirs. All four units were in commercial operation by April 2026.
• Srisailam (Telangana, left bank): 900 MW.
• Purulia (West Bengal): 900 MW.
• Nagarjuna Sagar (Telangana): about 705 MW.
• Kadamparai (Tamil Nadu): 400 MW.
• Bhira and Ghatghar (Maharashtra): 150 MW and 250 MW.

Government plans and policy

• In March 2019, the government declared large hydropower (above 25 MW) as a renewable energy source, which helps pumped storage too.
• In 2023, the Ministry of Power issued Guidelines to Promote Development of Pump Storage Projects. They suggest states ease land and tax costs and allow flexible ways to allot sites.
• In January 2026, the Central Electricity Authority (CEA) released a Roadmap to 100 GW of Hydro Pumped Storage Projects. The target is about 100 GW by 2035-36. India's identified potential is about 267 GW, and over 75% of it is off-river closed-loop. Maharashtra has the largest identified potential (over 56 GW).

Commonly confused concepts

• Pumped storage vs conventional hydropower: A normal hydro plant only generates electricity from river flow. Pumped storage mostly stores electricity made elsewhere; it uses more power than it gives back, but it gives it back when power is most valuable.
• Pumped storage vs battery storage (BESS): Batteries (like lithium-ion) are fast to build and suited for 2 to 4 hours of storage. Pumped storage costs more upfront but can store energy for 6 hours or more and lasts for decades.
• Open-loop vs closed-loop: Open-loop is connected to a flowing river. Closed-loop is not.
• Storage vs generation capacity: A plant's MW tells how much power it gives at once. MWh (or hours of storage) tells how long it can keep giving it.

Issues, criticism and the way forward

• High upfront cost and long build time: Big civil works like tunnels and dams take years and cost a lot.
• Environmental concerns: Projects in hills and forests can affect forests, wildlife corridors and local communities. The Purulia project faced criticism about its impact on elephant habitats. Environmental groups oppose relaxing impact studies for such projects.
• Suitable sites: Good sites need two reservoirs close together with a large height difference.
• Way forward: Prefer off-river closed-loop sites, speed up clearances without skipping safety checks, and use long-term contracts that pay for the storage service so that projects are financially viable.

Concepts to Know

• Peak demand: The time of day when electricity use is highest, in India usually the evening.
• Grid stability: Keeping the supply of electricity always equal to demand, so voltage and frequency stay steady and there are no blackouts.
• Variable speed unit: A pump-turbine whose speed can change. This lets the plant adjust its power more finely and help the grid better.
• Central Electricity Authority (CEA): India's main technical body for planning the power sector, under the Ministry of Power.
• Battery Energy Storage System (BESS): A large set of batteries connected to the grid to store and release electricity.