Definition
Solar distillation is the process of purifying water using solar energy. It mimics the natural water cycle, where water evaporates due to the sun’s heat, condenses on a cool surface, and is collected as distilled (pure) water.
Principle
Solar distillation is based on:
- Evaporation of impure water by solar heat
- Condensation of water vapor on a cooler surface
- Collection of pure, distilled water
This principle is identical to the natural hydrological cycle:
Sunlight → Water Evaporation → Condensation → Precipitation
Working Mechanism of Solar Still (Single Basin Type)
Structure:
- Basin: Shallow container holding impure/saline water
- Transparent Cover: Usually glass or plastic sheet, sloped to allow condensed water to run off
- Condensation Surface: Inner surface of transparent cover
- Distillate Channel: Collects condensed pure water
- Insulation: Reduces heat loss from bottom/sides
Working:
- Solar radiation passes through the transparent cover and heats the water in the basin.
- Water evaporates, leaving salts and impurities behind.
- Water vapor condenses on the inner cooler surface of the sloped cover.
- Condensed water flows down the cover and is collected in a distillate trough.
Types of Solar Distillation Systems
Type | Description |
Single Basin Solar Still | Most common; simple structure |
Double Slope Solar Still | Higher yield, slopes on both sides |
Multi-Basin or Multi-Effect | More efficient, layered basins |
Wick Type Solar Still | Uses capillary action for faster evaporation |
Floating Solar Still | Used in ponds or lakes, floats on water |
Factors Affecting Efficiency
- Solar radiation intensity
- Ambient temperature
- Basin water depth (1–5 cm optimal)
- Glass cover material & slope
- Wind speed and cooling on glass surface
- Insulation and heat losses
Applications
Application | Use |
Drinking Water | Desalination of seawater or brackish water |
Hospitals | Pure water for medical use |
Laboratories | Distilled water for experiments |
Rural & Remote Areas | Drinking water supply without electricity |
Livestock | Supplying clean water to animals |
Small-scale Industries | For chemical mixing and product quality |
Advantages
- Uses abundant, free solar energy
- Low maintenance, simple technology
- Can work in remote or off-grid areas
- Produces high-purity water
- Environmentally friendly
Limitations
- Low distillation rate (~2–5 liters/m²/day)
- Requires large surface area for higher output
- Only works in sunny climates
- Initial cost may be high for large units
- Not suitable for large-scale water needs
Performance
Parameter | Typical Value |
Output | 2–5 liters per m² per day |
Operating Temp | 60–80°C |
Efficiency | ~30–50% (thermal) |
Best Angle of Glass | Equal to local latitude ±10° |
Enhancements for Improved Efficiency
- Use of black-coated basin to absorb more heat
- Reflectors to increase solar input
- Vacuum insulation to reduce heat loss
- Use of phase change materials (PCMs) for heat storage
- Preheating input water using solar collectors
Real-World Examples
- Gujarat, India: Solar stills used for coastal desalination in remote villages
- Africa/Middle East: Solar distillation used in arid areas for safe drinking water
- Research Labs: Testing solar stills in combination with greenhouses and solar concentrators
