Solar heat from a collector can be transported by air, instead of water. No anti-freeze is needed and a possible leak causes no damage.

Over the years this technology has been used in the renovation of many houses, schools and industrial buildings [7]. An example of a very practical application, solar heating second homes, is given here.

Often after a stone rustico or wooden chalet in the Alps, log cabin in Scandinavia or masonry cottage in the Mediterranean has been purchased, it must be renovated. While vacant it becomes cold, damp and mouldy. When the owners arrive, the air and bedding smell musty and it likely takes forever to bring the mean radiant room temperature up to a comfort level. Too often the solution is an electric resistance heater set at a low temperature during the owner’s absence. Because occupancy is only for short intervals, investment in insulation or better windows is difficult to justify. Thus, the auxiliary heating, even at a low temperature setting, consumes much energy. Solar air collectors can deliver sun-warmed air by free convection thereby maintaining a minimum room temperature and dryness. Optionally, a small pv-powered fan can increase the air flow and hence collector efficiency. Figure 7 shows an application in Koroni, GR. The two 6m2 collectors each include a 50Wp pv section to power the circulation fans which can circulate up to 200m3/h. [8].