The surface area of the solar systems in operation in Greece is around 2.800.000 m2 (data for 2001). Already, more than 1.000.000 Greek families cover almost 80% of their yearly needs for hot water with solar water heaters. The efficiency and quality of solar collectors have generally improved in recent years. Greece is the largest exporter of solar water heaters in Europe, even to countries with a long industrial tradition, such as Germany.
A typical solar hot water production system is composed of solar flat plate ollectors, a heat storage vessel and piping. Solar radiation is absorbed by the collector and the heat collected is transferred to the storage vessel. The solar collectors are usually placed on the roof of the building, facing south and at an inclination of 30? – 60? with respect to the horizontal plane, so as to optimize the amount of radiation collected on a yearly basis.
Besides household use, which is the most common at present, active solar systems can be used anywhere low temperature heat is needed. Thus, the use of solar energy for the production of cooling, for air conditioning buildings and other applications, is emerging as one of its most promising prospects because of the increased solar radiation at precisely the season when cooling loads are greatest. There are already some successful applications of such systems in Greece, and it is expected that they will develop rapidly.
Another solar thermal application which has become widespread in the European market is the combined production of hot water and space heating . The use of these systems under Greek climate conditions for heating buildings is considered to be both technically and economically profitable if it is combined with a suitable design/construction of the building (good insulation, use of passive solar gains, etc.). A substantial part of conventional energy can be saved in new or old buildings where all possible measures have been taken to minimize losses and maximize the efficiency of the structure.