Introduction

A solar dryer is a sustainable innovation that leverages solar energy to effectively dehydrate materials especially food items like fruits and vegetables. Unlike traditional sun-drying methods that expose food directly to the elements, solar dryers offer a cleaner and faster alternative. The device captures sunlight, converts it into thermal energy, and traps this heat within a controlled environment. This enclosed chamber circulates warm air around the food, speeding up moisture evaporation while maintaining hygiene and protecting it from dust, insects, and unpredictable weather.

Type of Solar Dryers:

On the basis of shape it divided into three types are as follows :

1. Flat Dryer

  • Shape & Volume: Box type, 0.5026 m³
  • Drying Capacity: 2 kg
  • Drying Time: 2 days
  • Air Circulation: Natural air circulation
  • Energy Used: Solar illumination
  • Absorber Plate Area: 1.64 m²
  • Materials Used:
    • Base: MS L frames
    • Bed walls: Polycarbonate sheet
    • Absorber plate: Polycarbonate sheet
Fig. Flat bed Dryer

2. Dome Dryer

  • Shape & Volume: Dome-shaped, 0.78345 m³
  • Drying Capacity: 100kg
  • Drying Time: 2 day
  • Air Circulation: Forced air circulation
  • Energy Used: Electricity / Solar illumination
  • Absorber Plate Area: m²
  • Materials Used:
    • Base: Plywood circular plate
    • Stand and tray: MS tubes
    • Dome: Made from sheet metal
DEHYDRATION OF VEGETABLES :-
Fig. Dome Dryer

3. Inclined Dryer

  • Shape & Volume: Inclined plane, 2.2 m³
  • Drying Capacity: 7.3 kg
  • Drying Time: 1 day
  • Air Circulation: Forced air circulation
  • Energy Used: Electricity
  • Efficiency: 41.39%
  • Absorber Plate Area: 11.97 m²
  • Materials Used:
    • Surface: Sheet metal with black paint coating
    • Chamber walls: PVC sheets with black cloth paper
    • Components: Absorber box, air circulation box, insulating foam
Fig. Inclined Dryer

Factor Affecting drying

1. Temperature

Higher temperature = faster drying

  • Warmer air holds more moisture.
  • It increases the rate of evaporation from the wet surface.

Lower temperature slows evaporation because the air can’t hold as much moisture.

2.Humidity

Low humidity = dry air = absorbs more moisture from the surface = fast drying.

High humidity = air is already full of moisture = evaporation slows down

3. Air Flow ( wind )

Increased wind removes the moist air layer above the drying surface.

It keeps replacing humid air with dry air, boosting evaporation.

No wind = stagnant humid air near the surface = slower drying

4. Solar Irradiance

First trial on SUBABUL in Flat bed dryer

On first trial we consider readily available plants leaves SUBABUL. In Vigyan Ashram compass abundance of Subabul is available. To make it useful for drying process we cut the leaves of subabul plant measurably to fit in the flat bed dryer.

Calculations

  • Initial weight of subabul leaves = 1.5 kg = 1500 g
  • Final (dry) weight (day 1) = 622 g
  • Drying time = From 12:50 PM to 5:30 PM = 4 hours 40 minutes = 4.67 hours ≈ 16,800 seconds

1. Moisture Removed:

Moisture Removed=1500 g−622 g=878 g

2. Moisture Content (Wet Basis %):

MC wb​=Initial Weight Moisture Removed /initial weight ​×100

=878/1500​×100=58.53%​

3.Moisture Content (Dry Basis %):

MC db=Moisture Removed /Final Dry Weight×100

=878/622×100=141.13%

4. Drying Rate (g water removed per second):

Drying Rate=878 g/16,800 s≈0.0523 g/s​

Or in per hour:

=878/4.67≈188.01 g/hr​