---
title: "How a geothermal power plant operates"
subject: "Power Plant Design"
chapter: 1
key: "semester_8/power_plant_design:geothermal-plant-operation"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/geothermal-plant-operation
site: BCT Engineering
---

# How a geothermal power plant operates

Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation

- Asked in: 2071 Bhadra, 4 marks
- Video: [Geothermal Power Plant](https://www.youtube.com/watch?v=eyOXmqu4PS8) — Cognifront Products
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/geothermal-plant-operation
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1

## Question

How does a geothermal power plant operate? Describe briefly.

## Short answer

Production wells bring hot pressurized water or steam to the surface; a separator flashes water into steam, which drives a turbine and generator. Exhaust steam condenses, and condensate and brine are reinjected into the reservoir. Plants run continuously as base load with about 90% capacity factor.

## Answer

A **geothermal power plant** produces electricity from the heat of hot water or steam taken from underground reservoirs through wells. It works on a steam (Rankine) cycle like a thermal plant, but the boiler is replaced by the earth.

#### Operation (flash steam plant, most common)
```text
 Prod. well -> Separator -> Steam -> Turbine -> Gen
                  |                    |
                Brine              Condenser <- Cooling
                  |                    |        tower
                  +-> Injection well <-+
```
1. **Production well** brings hot, pressurised water (about 180–300 °C) to the surface.
2. In the **separator/flash tank** the pressure drops, part of the water flashes into steam.
3. The steam drives the **turbine**, which turns the **generator**.
4. Exhaust steam is condensed in a **condenser**, cooled by a cooling tower.
5. Condensate and separated brine are **reinjected** into the reservoir to maintain pressure and avoid pollution.

#### Other types
- **Dry steam**: steam directly from the well to the turbine (e.g. The Geysers, USA).
- **Binary cycle**: moderate-temperature water heats an organic fluid (isobutane) in a heat exchanger; its vapour drives the turbine.

Geothermal plants run continuously as base-load plants with high capacity factor (about 90%).

## Check yourself

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

1. How does a geothermal plant differ from a thermal plant?
   A. The earth's heat replaces the boiler
   B. It uses a Brayton cycle with no steam
   C. It uses a diesel engine
   D. It has no turbine
   Answer: A. It works on a Rankine steam cycle with the earth as the heat source. (Key point: Replaces the boiler)

2. What happens in the separator/flash tank?
   A. Steam is condensed
   B. Pressure drops and part of the hot water flashes into steam
   C. Brine is heated
   D. Steam is stored
   Answer: B. The pressure drop flashes some water to steam, which drives the turbine. (Key point: Flash separator)

3. Why are condensate and brine reinjected?
   A. To increase turbine speed
   B. To maintain reservoir pressure and avoid pollution
   C. To cool the generator
   D. To make steam hotter
   Answer: B. Reinjection sustains the reservoir and avoids disposing of brine at the surface. (Key point: Reinjection)

4. In a dry steam plant, steam
   A. goes to a heat exchanger first
   B. is flashed in a separator
   C. goes directly from the well to the turbine
   D. is produced by burning coal
   Answer: C. Dry steam plants feed well steam straight to the turbine. (Key point: Dry steam vs flash)

## Related in Power Plant Design

- [Geothermal versus conventional thermal plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ageothermal-vs-thermal) — Power Plant Design, chapter 1
- [Geothermal energy uses and plant types in Nepal](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ageothermal-use-nepal) — Power Plant Design, chapter 1
- [Thermal, geothermal and nuclear plants compared](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-geothermal-nuclear) — Power Plant Design, chapter 1, asked 7×
- [Thermal, geothermal and PV plants compared](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-geothermal-pv) — Power Plant Design, chapter 1, asked 7×
- [Biomass compared with geothermal energy](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abioenergy-vs-geothermal) — Power Plant Design, chapter 1
- [Thermal versus nuclear power plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-vs-nuclear) — Power Plant Design, chapter 1, asked 2×

## Related in other subjects

- [Types of geothermal power plant](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ageothermal-plant-types) — Energy Environment and Society, chapter 3
- [Simple Rankine plant 2 MPa / 20 kPa: efficiency, power](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Arankine-2mpa-20kpa-50kgs) — Fundamental of Thermodynamics & Heat Transfer, chapter 6
- [Layout of diesel power plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-plant-layout) — Power Plant Equipment, chapter 5, asked 3×
- [Types of power supply system for industrial plant](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aindustrial-supply-system-types) — Industrial Power Distribution and Illumination, chapter 1, asked 2×