Solar water heaters

Solar water heaters (SVA heaters) are intended for receiving hot water by means of transformation of solar energy without additional use of traditional power sources: gas, electricity, solid or liquid fuel. Solar water heaters can be active or passive types. The active system uses the electric pump for circulation of liquid through a collector; the passive system has no pump and it is necessary only on natural circulation. There are experimental samples where transfer of the heat carrier is made by the stirling-pump, receiving energy from the sun.
Passive systems
Passive (Thermosiphon) systems move ready water or the heat carrier through system due to the natural gravitation arising at a difference of density of the heated and cooled heat carrier. Passive systems with convection are cheaper, than active systems, but also are less effective because of slow circulation in system. Systems with thermal pipes more expensive, than convective but have smaller operational expenses. Besides, systems with thermal pipes allow to pump over warmly down, that is against convection forces. Characteristics strongly depend on concrete type of pipes. Active systems use electric pumps, valves and controllers for circulation of the heat carrier through a collector. They are usually more expensive, than passive systems, but also are more effective.
Active systems with an open contour
Active systems with an open contour use pumps for circulation of water through collectors. Active systems with an open contour are popular in regions with positive temperatures or at seasonal use. Can be operated at air temperatures to −20 by °C or −25 in °C.
Active systems with the closed contour
In these systems the heat carrier of a collector is usually water glikoliyevy antifreeze. Heat exchangers transfer high temperature from the heat carrier of the first contour to water which is reserved in tanks (heataccumulators). Systems with the closed contour are popular in the areas which are exposed to temperatures which are for a long time operating negative as they have good protection against freezing. Due to the high values of temperature at stagnation of the heat carrier during the periods of the maximum obluchennost, not all antifreezes are suitable for use in solar systems.