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

# Short note: Solar dryer

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: 2070 Asar, 2 marks
- 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-dryer
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

Write a short note on solar dryer.

## Short answer

A solar dryer uses solar heat to dry crops more quickly and cleanly than open sun drying. Types include direct, indirect, mixed-mode, and forced convection. Heated air reduces moisture, preserving quality. It is used in Nepal for chilli, genger, cardamom, and herbs.

## Answer

A **solar dryer** uses solar energy to remove moisture from agricultural products such as grains, vegetables, fruits, herbs, fish and timber. It is faster, cleaner and more hygienic than open sun drying, which suffers from dust, insects, birds and rain.

#### Types
1. **Direct (cabinet) dryer:** the product is placed in a box with a transparent cover; sunlight strikes it directly.
2. **Indirect dryer:** air is heated in a separate solar air collector and then passes over the product, so the product is not exposed to sunlight (keeps colour and vitamins).
3. **Mixed-mode dryer:** combination of both.
4. **Forced convection dryer:** a fan (often PV powered) drives the air flow.

```text
 Air in -> [Solar air collector] -> [Drying chamber with trays]
                                          |
                                   moist air out (chimney)
```

#### Advantages
- Saves fuel or electricity; uses free energy.
- Gives higher temperature and lower humidity, so drying is faster.
- Better quality of the product, protection from pests, and less loss.
- Used in Nepal for chilli, cardamom, ginger, apple, herbs, fish and tea in the hills.

Limits: depends on weather and sunshine, and needs initial investment.

## Check yourself

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

1. What is special about an indirect solar dryer?
   A. Air is heated in a separate collector, so the product is not exposed to sunlight
   B. Product is placed directly under glass in sunlight
   C. A fan is the only heat source
   D. It is used only at night
   Answer: A. Not exposing the product to sunlight keeps colour and vitamins. (Key point: Indirect dryer)

2. Why is a solar dryer better than open sun drying?
   A. It needs no sunlight
   B. It lowers drying temperature
   C. It costs nothing to build
   D. It is faster and protects from dust, insects, birds and rain
   Answer: D. Higher temperature and lower humidity speed up drying and protect quality. (Key point: Advantage over open drying)

3. What does a forced convection dryer use?
   A. A chimney only
   B. Mirrors for focusing
   C. A fan, often PV powered, to drive airflow
   D. A thermosiphon tank
   Answer: C. Forced convection uses a fan; natural convection relies on buoyancy. (Key point: Forced convection)