---
title: "Solar thermal energy and application"
subject: "Energy Environment and Society"
chapter: 3
key: "semester_7/energy_environment_and_society:solar-thermal-application"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/solar-thermal-application
site: BCT Engineering
---

# Solar thermal energy and application

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: 2071 Chaitra, 4 marks
- Video: [Solar Thermal Energy: Harnessing the Power of the Sun](https://www.youtube.com/watch?v=w9Oy3VOPEgs) — RESHEAT
- 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/solar-thermal-application
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

Write about solar thermal energy and its application.

## Short answer

Solar thermal energy captures sunlight as heat using flat-plate or concentrating collectors. Applications include water and space heating, solar cooking, crop drying, desalination, industrial process heat, and electricity generation via CSP with steam turbines.

## Answer

**Solar thermal energy** is the use of solar radiation as heat. Sunlight is absorbed by a surface (the absorber), which converts it into heat that warms a fluid (water, air or oil). The heat is used directly or to run a heat engine for electricity. It does not use photovoltaic cells.

#### Main components
A collector (flat-plate or concentrating) with a black absorber, transparent cover glass, insulation, a heat transfer fluid, and a storage tank. Flat-plate collectors give low temperatures (up to 80–100 °C); concentrating collectors (parabolic trough, dish, tower) give medium to high temperatures (150–1000 °C).

```text
 Sun ---> [Glass cover]
          [Absorber plate + tubes] --> hot water
          [Insulation]                  to tank
```

#### Applications
1. **Water heating:** domestic and commercial solar water heaters (common in Nepal's urban homes, hotels and hospitals).
2. **Space heating and cooling:** passive solar buildings, absorption cooling.
3. **Cooking:** box-type and parabolic solar cookers.
4. **Drying:** solar dryers for crops, fruits, herbs and timber.
5. **Desalination and distillation:** solar stills.
6. **Industrial process heat:** pasteurisation, dairy, textile.
7. **Electricity generation:** concentrating solar power (CSP) plants with steam turbines, with heat storage in molten salt.
8. **Greenhouse heating and swimming-pool heating.**

## Check yourself

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

1. How does solar thermal energy differ from PV?
   A. It converts light directly to electricity
   B. It stores sunlight in batteries
   C. It uses only wind
   D. It absorbs radiation as heat in a fluid, without photovoltaic cells
   Answer: D. Solar thermal uses an absorber to heat water, air or oil. (Key point: Solar thermal)

2. Which collectors give medium to high temperatures (150-1000 deg C)?
   A. Flat-plate collectors
   B. Passive walls
   C. Concentrating collectors such as trough, dish and tower
   D. Solar stills
   Answer: C. Flat-plate gives up to 80-100 deg C; concentrating collectors reach much higher temperatures. (Key point: Collector temperatures)

3. How does a CSP plant generate electricity and store heat?
   A. PV cells with batteries
   B. Steam turbine, with heat stored in molten salt
   C. Wind turbine on a mirror tower
   D. Direct conversion in a fuel cell
   Answer: B. CSP makes steam for turbines and can store heat in molten salt. (Key point: CSP storage)

4. Which is a main part of a flat-plate collector?
   A. Black absorber, transparent cover and insulation
   B. Silicon p-n junction
   C. Proton exchange membrane
   D. Penstock
   Answer: A. Flat-plate collectors have a black absorber, glass cover, insulation and fluid tubes. (Key point: Components)

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