The last two decades a lot of efforts have been done by the researchers in different countries in order to study the possibilities of using solar energy for heating greenhouses. From these research works hundreds of solar systems have been developed, but out of these very few found practical application. The passive solar system with the water filled plastics tubes and the system of spraying water on the top of the greenhouses are the only solar systems adapted by some growers of the greenhouses in the Mediterranean

In the simple Mediterranean plastics greenhouses during cold seasonal large diurnal changes of air temperatures take place mainly during weather conditions of clear sky. In such conditions during night the minimum air temperatures often drop to much lower than the accepted levels and the maximum air temperatures increase above the desired levels.

The passive solar systems work with natural way, provide heat and a thermal buffer into the greenhouse without requiring external energy sources, are simple, easily understood, inexpensive, aesthetically more attractive than ordinary active systems and can operate even when the active systems fail The principal disadvantages of the passive systems are the little or no control and the difficulty to integrate the solar collection and storage facilities into the greenhouse architecture.