SEMI-SPHERICAL SOLAR COLLECTOR FOR WATER HEATING

In Latvia because of its geographical and climatic conditions there are some features in use of the solar energy. There is a long path of the sun at summer, but frequently large nebulosity, which enlarges the necessity to receive the energy from all sides. Therefore, conditional flat plate solar collectors are not efficient enough, but new constructions of solar collectors are required. One of such new constructions can be a semi-spherical solar collector, capable to receive the solar energy from all sides. Such semi-spherical solar collector with radius 0.56 m that corresponds to the base area 1 m(2) has been made, and measurements of water heating have been carried out at summer 2009. Theoretical calculations of the energy gain from such collector have been performed and verified by comparison of the calculated daily energy sums with the measured ones, and good coincidence has been obtained. The results obtained from these calculations show, that the energy gain from the semi-spherical solar collector with the base area 1 m(2) is similar to that of tracking to the sun flat collector of 1 m(2) area. The tracking to the sun solar collector is complicated, expensive and not durable, but the semi-spherical solar collector is simpler, durable against the impact of wind and with good appearance. The measurements show, that the energy gain from such semi-spherical solar collector, made of simple materials, is similar to that from 1 m(2) of the industrially manufactured vacuum tubes solar collector. The energy gain from the semi-spherical solar collector can be increased by using in its construction contemporary special materials and technologies, such as special absorbing colours and selective coatings.