Most solar hot water systems use solar collectors or panels to absorb energy from the sun. Water is heated by the sun as it passes through the collectors. It then flows into an insulated storage tank for later use.
In passive systems, water flows due to a thermosiphon effect between the collectors and the tank. In active systems, water is pumped between the collectors and the tank.
The storage tank is usually fitted with an electric, gas or solid fuel booster that heats the water when sunlight is insufficient. Some solar water heaters also have frost protection to prevent damage in frost prone areas.
Water heating accounts for 25 per cent of the energy used in an average home and is responsible for 23 per cent of the total greenhouse gas emissions from home energy use. Reducing your hot water use and using renewable energy sources to heat water are great ways to reduce your environmental impact.
By installing the most appropriate and efficient water heater for your household size and water use patterns you can save money and reduce greenhouse gas emissions without compromising your lifestyle. An efficient hot water system can also add value to your home and help you to meet local council or state/territory regulations.

Solar center heating project for school, hotel, swimming pool Many solar thermal collectors can be linked together for making solar central heating project, such as in hotel, school, even swimming pool which need a lot of hot water every day. The project capacity can be from 1000L-100000L, It needs solar collectors, storage tank, controller, circulation pump and pipeline etc to be combined with. An assistant heating system, such as heat pump, boiler can be connected with, to provide the hot water in everytime.

The angle and direction of installation is also of great importance as it will effect the efficiency of the solar collector. Naturally you want the collector to receive the maximum amount of sunlight each day and throughout the year. As a general rule if you are in the Northern Hemisphere then the collector should face South and if you are in the Southern Hemisphere then the collector should face North. See diagram below.

The angle at which you mount the collector should roughly correspond to the latitude of your location. For example:
- Melbourne, Australia has a latitude of 37o South - the collector should therefore face north at a 37o angle.
- London, UK has a latitude of 51o North - the collector should therefore face south at a 51o angle.

You do not have to be too careful about mounting the collector at the exact angle suggested. If your roof angle is within 10o+/- of your desired angle you can just mount the solar collector flush against the roof surface. The added trouble of adjusting the collector to a precise angle is not warranted as it will not result in a great improvement in efficiency.
About 30 per cent of the energy used to heat water in a storage system is wasted due to heat loss from the tank and associated pipework. This can be reduced through careful design and installation.
Keep hot water pipes as short as possible to minimise heat loss. In new or renovated homes, locate wet areas close together with the water heater close to all points of hot water use. If this is not possible, locate it close to the kitchen where small, frequent amounts of hot water are used. Another alternative is to install a water recirculation system. These systems are generally compatible with any hot water system type. They recirculate water in the pipes until hot water is detected, to avoid wastage.
Estimate your hot water needs accurately to ensure your system is not oversized or undersized for your household. If storage system tanks are too small for the number of people in the house hot water can run out. If the tank is too large, operating costs will be excessive.
Storage systems lose heat through the tank walls. Reduce heat loss from electric hot water heaters by wrapping the tank with an insulation blanket. Insulation blankets are unsuitable for gas storage systems.
Insulate hot water pipes, particularly externally exposed pipe leading from the water heater to the house and the pipe leading to the relief valve (on storage systems). Note: Standard green lagged hot water pipes are inadequate for external protection in cold and cool temperate climates. Apply additional insulation or 'lagging'. At least 10mm of foam insulation is needed.
The tempering valve, required to limit hot water to 50^oC to prevent scolding, should be located as close as possible to the tank to minimise pipe heat losses. Be sure to comply with your state or territory government requirements.
For storage systems consider installing a timer to ensure water is not heated when it's not needed, and a switch so the system can be turned off when you go on holiday.
Design new homes with a roof pitch and orientation suitable for a solar water heater. You may not want to install one now but it leaves the option open for the future. A north-facing roof with a pitch of between 22^o and 40^o is usually adequate.

The controller monitors the temperature difference between circulatory medium and the water in tank.The pump starts to work for heat exchange when temperature of circulatory medium is higher than water's in the tank also the water temperature is not higher than the settled date; The pump shuts off and the heat exchange stops when temperature of circulatory medium is lower than water's in the tank or the water temperature is higher than the value settled,
Description for System Control Principle:
1)Heating cycle: the circulatory system adopts constant temperature and temperature difference cycle, in case T1(collector temperature)-T2(tank water temperature)≥5^oC,meanwhile T2≤80^oC(settled temperature), the pump starts for transferring the high heat medium in the collector into heat exchange coil to heat up the lower temperature water in tank;The pump stops operating while T1-T2 <2^oC;The pump shuts off when T2>80^oC.
2)Frost prevention of system:The controller starts the pump for exchanging the heat of the water into coil when T1(collector temperature)≤3^oC(settled temperature),;The controller stops pump when T1≥6^oC.
3)Overtemperature protection of system:when T1(collector temperature)≥99^oC,the system brings high pressure and it will be absorbed by expansion tank(18-24L) (Remark: Since the collecting area is smaller in individual system, around 3-6 square meters, the expansion pressure caused by high temperature or gasification is smaller, and it can be absorbed by expansion tank); Besides the collecting system equipped with relief valve, it can exhaust to protect the system (under some extreme condition).
4)Independent system for individual house, independent calculation for electricity and water consumption, easy to manage;Water and collection are complete separated, fouling-free in collector, high absorbing efficiency;Pressured water tank more comfortable.

Solar collectors heat the water,circulation is controlled by the temperature difference between hot water in the collectors and cold water in the tank with a circulating pump, and then provide hot water to all users.Auxiliary heater will start if water temperature can not reach the settled temperature when the light is insufficient.
Description for system control Principle
1)Circulation of main pipe:The circulatory system adopts constant temperature and temperature difference,if T1(collector temperature)≥60^oC(Purpose is to prevent running pump all the time,it is settled up to local condition),meanwhile T1-T2(temperature of circulatory medium in main pipe)≥8^oC, the system controller makes the circulating pump to start,heated medium transfer to main pipe loop; The system controller makes the circulating pump to shut down,if T1 <50^oC;The system controller makes the circulating pump to shut down and the heat circulating stop when T1-T2≤2^oC.
2)Circulation of branch pipe:The branch circulatory system adopts constant temperature and temperature difference,if T3(water temperature of users'tank)≤80^oC(settled temperature), meanwhile T2(inlet temperature of main pipe)-T3≥8^oC,indoor controller opens electromagnetic valve of branch pipe, let heating medium get into heat exchange coil to make circulating;The indoor controller will shut off the electromagnetic valve of branch pipe if T3>80^oC;The indoor controller will shut off the electromagnetic valve of branch pipe when T2-T3 <2^oC.
3)Frost prevention of system: low power electrical heater is installed on main pipe (bypass),the controller turns on the heater,the electromagnetic valve and the circulatory pump for carrying out the frost prevention circulating when T1(collector temperature)≤3^oC(settled temperature);The system controller shuts off the heater,electromagnetic valve and the pump when T1≥6^oC,the prevention stops.
4)Overtemperature protection of system:The controller turns on the electromagnetic valve and circulatory pump for radiating cycle proceeds through radiator when T1(collector temperature)≥99^oC;The system controller shuts off the circulatory pump and the electromagnetic valve;The overtemperature protection stops when T1≤90^oC.