Articles
A SOLAR GREENHOUSE BASED ON WATER SLEEVES AND A MOVABLE THERMAL SCREEN FOR USE IN ARID REGIONS
The system is based on a combination of two components:
- water sleeves, which function as a passive element for the day-time collection of solar energy that is then used for warming, mainly during the night; and
- a movable thermal screen, which is spread over the plants at night to reduce heat loss to the surroundings.
The solar greenhouse is designed to operate as a closed system most of the winter to enable maximal solar energy storage in the sleeves.
This concept was applied to melon production, as a test crop to assess whether high-quality fruit could be obtained during the winter for export to Europe.
The experiment was carried out in six identical tunnels, 4 m wide, 11 m long, and 2 m high.
Average increase of the water temperature in the sleeves was about 7.5°C on a clear day compared with about 4°C on a cloudy day.
On a typical clear night following a sunny day air temperatures in the greenhouse at a height of 0.5 m above the ground were 6–7°C higher than outdoor temperatures, and comparable soil temperatures (at a depth of 20 cm) were 8.5–9°C higher indoors.
After a cloudy day this difference in air temperature was reduced to about 5°C. On the assumption that there are 120 growing days per season, the average energy stored in the water sleeves was estimated to be equivalent to 4.2–7.5 kg/m2 of petroleum per season.