Solar Water Heaters

Working Principle:
passive systems
Thermosyphon solar water heater is open to air and relies on water’s natural circulation. When water in vacuum tube is heated, it rises naturally into storage tank, while cold water in storage tank flow back vacuum tube .
A thermosiphon system relies on warm water rising, a phenomenon known as natural convection, to circulate water through the solar absorber and to the tank. In this type of installation, the tank must be located above the absorber tubes/panel. As water in the absorber heats, it becomes lighter and naturally rises into the tank above. Meanwhile, cooler water in the tank flows downwards into the absorber, thus causing circulation throughout the system. This system is widely used with both flat plate and evacuated tube absorbers.

Active Systems
Active solar water heater systems use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. They are usually more expensive than passive systems but generally more efficient. Active systems are often easier to retrofit than passive systems because their storage tanks do not need to be installed above or close to the collectors. If installed using a PV panel to operate the pump, an active system can operate even during a power outage.

The cold water supply is connected to the solar storage tank. Water to be heated circulates between the storage tank and the solar collectors. The output from the solar storage tank becomes the cold water connection to the conventional gas, electric or oil water heater. When a hot tap is opened, pre-heated water is drawn from storage into the conventional  water heater. The burner or electric element turns on only if the temperature cannot be maintained by the solar heater. Most properly-designed solar water heaters will supply 70 per cent or more of all the energy needed for water heating.

Types
There are two types of solar water heating systems: active, which have circulating pumps and controls,
and passive, which don't.

Compact solar water heater systems(passive systems)
A compact solar hot water system also known as a monobloc has a tank for the heated water and
a solar collector mounted on the same chasis. Typically these systems will function by natural
convection (thermosiphon) or heatpipes to transfer the heat energy from the collector to the tank

solar water heater with all glass vacuum tube.
Evacuated Tube solar water heater are made up of
rows of parallel, glass tubes. There are several types of evacuated tubes (sometimes also referred to as Solar Tubes). Glass-Glass) tubes consists of two glass tubes which are fused together at one end. The inner tube is coated with a selective surface that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss. These tubes perform very well in overcast conditions as well as low temperatures. Because the tube is 100% glass, the problem with loss of vacuum due to a broken seal is greatly minimized. Glass-glass solar tubes may be used in a number of different ways, including direct flow, heat pipe, or U pipe configuration. SunSurf uses a high efficiency heat
pipe and heat transfer fin design to conduct the heat
from within the evacuated tube up to the header. For
more information about heat pipes

solar water heat with heatpipe
A heat pipe is a simple device that can quickly transfer heat from one point to another. They are often referred to as the "superconductors" of heat as they possess an extra ordinary heat transfer capacity & rate with almost no heat loss.

heatpipe

flat plate solar water heater (passive system)
Flat -plate collector（solar water heater）
Glazed flat-plate collectors are insulated, weatherpro ofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

The separated solar water heater system could be
mounted on the southern roof of the villadom,
on the courtyard lawn, or the southern slope
of the construction. The hot water could be delivered
to any floor without limitation. The system has adopted the forced circulation (automatic control) work module to control the temperature automatically and deliver water by pressurization. So it has solved the long time inconveniences of manual operation. The system only needs small amount of investment, and it’s easy to handle. Moreover, it’s safe, convenient and energy saving, causing no pollution to the environment, so it’s complemented as “Green Project” by the experts.