---
title: "Short note: Pumped storage hydropower"
subject: "Energy Environment and Society"
chapter: 5
key: "semester_7/energy_environment_and_society:pumped-storage-hydropower"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/pumped-storage-hydropower
site: BCT Engineering
---

# Short note: Pumped storage hydropower

Energy Environment and Society · Chapter 5: Energy Storage

- Asked in: year not given
- Video: [Deploying hydro pump storage technologies for clean energy | Matthew Stocks](https://www.youtube.com/watch?v=nTBE7F_2hIw) — World Economic Forum
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/pumped-storage-hydropower
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-5

## Question

Write a short note on pumped storage hydropower system.

## Short answer

Pumped storage pumps water to an upper reservoir with surplus power and releases it through a turbine to generate electricity. It provides large-scale, long-duration storage with 70–85% round-trip efficiency and a 50+ year lifespan, but requires special terrain.

## Answer

A **pumped storage hydropower (PSH)** plant stores energy as the gravitational potential energy of water, by moving water between two reservoirs at different elevations. It is the largest and most mature form of grid-scale energy storage in the world (it still holds most of the world's stored grid energy, although batteries are growing fast).

#### Working
- **Off-peak / surplus time:** cheap or surplus electricity (solar, wind, base-load plants) runs a reversible pump-turbine, pumping water from the lower reservoir to the upper reservoir.
- **Peak demand:** water from the upper reservoir is released through the turbine, generating electricity, and returns to the lower reservoir.

```text
   [Upper reservoir]
         |  penstock
   [Pump-Turbine / Motor-Generator]
         |
   [Lower reservoir]
 Pump mode: grid -> water up
 Generate mode: water down -> grid
```
Stored energy E = ρ g V H, and the energy recovered is about η ρ g V H. Round-trip efficiency is about 70–85%.

#### Advantages
- Large capacity and long duration (hours to days); long life (50–100 years).
- Fast response, black start capability, and grid stability (frequency and voltage control).
- Helps integrate solar and wind and offers a use for surplus monsoon electricity.

#### Disadvantages
- Needs suitable topography and water; high capital cost and long construction.
- Environmental impacts on land and water; energy loss of about 15–30% per cycle.

#### Nepal context
Nepal has surplus electricity in monsoon and a deficit in winter, so storage and pumped storage are options being studied for the future (for example proposals considered by NEA and private developers). Existing storage is limited, with Kulekhani being the only large reservoir plant.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. During off-peak surplus time, what does a pumped storage plant do?
   A. Releases water through the turbine
   B. Uses surplus electricity to pump water from the lower to the upper reservoir
   C. Burns fuel to heat water
   D. Electrolyses water
   Answer: B. Surplus power drives the reversible pump-turbine to lift water, storing gravitational potential energy. (Key point: Working principle)

2. In E = rho g V H eta, what does H represent and how does energy depend on it?
   A. Height difference between reservoirs; energy increases with H
   B. Humidity; energy decreases with H
   C. Heat; energy is independent of H
   D. Hours of operation; energy is inversely proportional
   Answer: A. H is the head (elevation difference); stored energy is proportional to volume and head. (Key point: Energy formula)

3. What is the typical round-trip efficiency of pumped storage?
   A. About 30-40%
   B. About 70-85%
   C. Over 99%
   D. About 10%
   Answer: B. About 70-85%, meaning around 20-30% energy is lost. (Key point: Efficiency)

4. Why is storage of interest in Nepal?
   A. Surplus electricity in monsoon but deficit in winter
   B. Too little electricity in monsoon
   C. Nepal has many large reservoir plants
   D. Demand is constant year-round
   Answer: A. Seasonal mismatch makes storage useful; Kulekhani is the only large reservoir plant. (Key point: Nepal context)

## Related in Energy Environment and Society

- [Hydropower requirements and components](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydropower-requirements-components) — Energy Environment and Society, chapter 3
- [Potentials and challenges of hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydropower-potential-challenges) — Energy Environment and Society, chapter 3

## Related in other subjects

- [Pumped storage plant and benefit to Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-benefit-nepal) — Hydropower Engineering, chapter 2
- [Pumped storage plant: power, turbine, setting, surge](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-turbine-surge-numerical) — Hydropower Engineering, chapter 7
- [Francis turbine in pumped storage plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Afrancis-turbine-pumped-storage) — Power Plant Equipment, chapter 1
- [When pumped storage is economically feasible](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apumped-storage-economic-feasibility) — Power Plant Equipment, chapter 1