---
title: "Pumped storage plant and feasibility in Nepal"
subject: "Power Plant Equipment"
chapter: 1
key: "semester_7/power_plant_equipment:pump-storage-nepal-feasibility"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/pump-storage-nepal-feasibility
site: BCT Engineering
---

# Pumped storage plant and feasibility in Nepal

Power Plant Equipment · Chapter 1: Hydro Power Plant

- Asked in: 2069 Chaitra, 8 marks; 2081 Bhadra, 6 marks; 2076 Chaitra, 5 marks; 2072 Kartik, 8 marks; 2071 Chaitra, 4 marks (asked 5 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/pump-storage-nepal-feasibility
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-1

## Question

Explain the operation of pump storage type hydro power plant with a neat diagram. Is this type of power plant feasible to install in Nepal's power system in the current scenario? Support your answer with appropriate reasons.

## Short answer

A pumped storage plant uses two reservoirs at different elevations. During off-peak, surplus electricity pumps water to the upper reservoir; during peak, water is released through a turbine-generator to produce power. In Nepal, it is feasible due to hilly terrain and run-of-river surplus, but dry-season deficit and high capital cost are challenges.

## Answer

A **pumped storage plant** is a hydro plant with two reservoirs at different levels. It uses cheap surplus electricity in off-peak hours to pump water from the lower reservoir to the upper one, and releases the same water back through the turbine to generate power during peak hours. It works like a large rechargeable battery for the grid.

```text
  UPPER RESERVOIR (head pond)
  ~~~~~~~~~~~~~~~~~~~~~~~
        |  penstock / pressure shaft
        |  (water flows down when
        |   generating, up when pumping)
        v ^
  +---------------------+      +-----------+
  | reversible          |------| motor-    |---- grid
  | pump-turbine        |      | generator |  (supply
  +---------------------+      +-----------+   or draw)
        | ^
        v |  tailrace
  ~~~~~~~~~~~~~~~~~~~~~~~
  LOWER RESERVOIR (tail pond)
```

**Main parts:** upper reservoir, lower reservoir (or river/tail pond), intake, penstock or pressure shaft, power house with a reversible pump-turbine (usually Francis type) coupled to a reversible synchronous motor-generator, and tailrace.

**Operation:**

1. **Generating mode (peak hours):** Water from the upper reservoir flows down the penstock, drives the machine as a turbine, and the machine works as a generator feeding the grid. The water is collected in the lower reservoir.
2. **Pumping mode (off-peak hours, e.g. night):** Surplus power from base-load plants (thermal, nuclear or run-of-river hydro) drives the machine as a motor. The machine rotates in the reverse direction and works as a pump, lifting water from the lower reservoir back to the upper reservoir.
3. The cycle repeats daily (or weekly/seasonally).

**Energy relation:** Energy stored $E = \rho g V H$. Overall cycle efficiency
$$
\eta_{cycle} = \frac{E_{generated}}{E_{pumping}} \approx 0.70 \text{ to } 0.80
$$
So about 1.3 kWh of off-peak energy is used to get 1 kWh at peak. It is still economic because peak energy is far more valuable than off-peak energy.

#### Feasibility in Nepal's power system

Pumped storage is **technically feasible and is becoming economically attractive in Nepal**, but it should be planned for the near future rather than treated as an immediate priority over storage projects. Reasons:

**Points in favour**
- **Topography:** Nepal's hills give high heads over short distances, so small reservoirs can store large energy.
- **Run-of-river dominance:** Most of Nepal's plants are run-of-river (ROR). They cannot follow the daily peak; the evening peak is hard to meet, while there is surplus at night.
- **Wet-season spill:** In the monsoon, ROR plants produce more than domestic demand. Off-peak surplus energy that is now spilled or sold cheaply can be used for pumping.
- **Cheap import / solar:** Off-peak energy can be imported from India at lower rates, and growing daytime solar can also be stored.
- **Grid support:** Quick start and reserve capacity improve frequency control of a small, weak grid.
- Existing reservoir sites such as **Kulekhani** (the only storage scheme of NEA) have been studied for adding pumped storage.

**Points against (in the current scenario)**
- In the **dry season** Nepal is itself energy deficit; there is little surplus energy to pump with, which is exactly when peaking power is most needed.
- **High capital cost**, long construction time and difficult access in the hills.
- Cycle losses of 20–30 %; it is economic only if the peak tariff is well above the off-peak price.
- Sediment-laden Himalayan rivers cause abrasion of pump-turbines and siltation of reservoirs.
- Seasonal storage projects (reservoir type) may give more benefit per rupee in a deficit system.

**Conclusion:** A daily-cycle pumped storage scheme is feasible in Nepal, especially using wet-season and night surplus, cross-border trade and solar. With proper tariff (time-of-day and seasonal pricing) and site selection, it can solve the peaking problem of an ROR-dominated system.

## Check yourself

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

1. How does a pumped storage plant use electricity over a day?
   A. It pumps water up using surplus off-peak power and generates with the same water at peak hours
   B. It generates at night and pumps during the evening peak
   C. It stores water only during the monsoon and never pumps
   D. It pumps water using its own generated output so no external energy is needed
   Answer: A. Cheap off-peak energy lifts water to the upper reservoir; releasing it through the turbine at peak hours gives valuable peak power. (Key point: Pumped storage principle)

2. With a cycle efficiency of about 70-80 %, roughly how much off-peak energy is needed to deliver 1 kWh at peak?
   A. About 0.75 kWh
   B. About 1.0 kWh
   C. About 1.3 kWh
   D. About 2.5 kWh
   Answer: C. 1/0.75 is about 1.3 kWh of pumping energy per kWh generated; it still pays because peak energy is worth much more. (Key point: Cycle efficiency)

3. Which feature of Nepal's present system makes pumped storage attractive?
   A. Most plants are run-of-river, so they cannot follow the evening peak but give surplus at night and in monsoon
   B. Nepal has mainly thermal plants that run at constant load
   C. Nepal has large reservoir plants that already meet every peak
   D. Nepal has a strong grid with no frequency problems
   Answer: A. ROR dominance means the evening peak is hard to meet while night and wet-season surplus is available for pumping. (Key point: Why it suits Nepal)

4. Which is the key argument against pumped storage in Nepal's current scenario?
   A. Nepal has no high-head sites
   B. In the dry season Nepal is energy deficit, so little surplus exists to pump exactly when peaking is needed
   C. Pump-turbines cannot work with Himalayan water
   D. Peak energy is cheaper than off-peak energy in Nepal
   Answer: B. Dry-season deficit, high capital cost and sediment are the main drawbacks; high heads are actually an advantage. (Key point: Main obstacle in Nepal)

## Related in Power Plant Equipment

- [Operation of pumped storage hydro plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-operation) — Power Plant Equipment, chapter 1, asked 2×
- [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
- [Pumped storage to reduce peak generation loss](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-peak-loss) — Power Plant Equipment, chapter 1, asked 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
- [Importance of storage plants; pumped storage layout](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Astorage-importance-pump-storage-layout) — Hydropower Engineering, chapter 2
- [Short note: Pumped storage hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apumped-storage-hydropower) — Energy Environment and Society, chapter 5