Solar collectors for northern countries

Abstract

Traditionally the solar energy has used in southern countries, but it has used also in northern ones. Most popular kind of use of the solar energy in Latvia is solar collector for water heating. Traditionally flat-plate solar collectors are used because of simplicity of manufacturing. However, some peculiarities in use of solar energy in northern countries must be taken into account. In northern countries there is lower irradiance, but longer day and longer path of the sun during summer. Therefore, traditional flat-plate solar collectors are not appropriate enough in northern countries and new forms have to be developed. There are two forms of solar collectors - cylindrical and semi-spherical – proposed in this work. Such collectors can be made for both water and air heating. Theoretical calculations and measurements of energy gain from those two collectors were carried out. Results show that daily energy sum received by the semispherical collector from the sun at the middle of summer is 1.43 times more than that of the flat one, but for the cylindrical collector it is 1.74 times more than that of the flat one, or equal to that of the tracking the sun flat-plate collector. Resulting difference in energy gain from collector will be not so large because of the difference in heat loses. Heat loses can be decreased by switching off the water circulation pump when the sun is covered by clouds. For these purpose circulation pump powered by solar batteries can be used instead of complicated and expensive automatics. Even more important than overall energy gain is the fact that semi-spherical and cylindrical collectors work all the day (17 hours in the middle of summer at 57 northern latitude), while flat-plate collector only about 11 hours. Yearly energy sum received by the collector from the sun is 1.5 and 1.9 times larger for the semi-spherical and cylindrical collector respectively as for the flat one. The cylindrical solar collector is easier to manufacture, but semi-spherical one is more aesthetical and durable against impact of the wind. Although solar collectors for water and air heating are studied in this article, main ideas are applicable also for solar batteries.