Solar hot water systems comprise many innovations and mature sustainable energy technologies and they have been established for many years and world widely used in many countries such as China, Japan, India, Australia and USA.

 

Generally, the solar hot water systems include a large storage tank and the solar collectors on the roof. The solar energy will be transferred into electricity to heat the water and maintain the water temperature. The water will be circulated by the pump from the ground to the roof and go through the solar heater. The heat transfer fluid between the tank and the collectors.

 

In general, there are 4 different types of solar water heating systems.

 

Direct Systems:

The direct, or open loop, systems circulate water from the ground to the solar collectors. The design of the direct systems are cheap and there are drawbacks to the system. The direct systems are not suitable for the cold climates. If there is no freeze protection, the collector will be damaged by freeze, pressurized water and the direct systems are not recommended.

 

Indirect Systems:

The indirect or closed loop systems use a heat exchanger that could separate the water from the fluid that circulates through the collector. The indirect system generally needs less maintenance cause the fluid is more thermally stable and carries fewer impurities. In addition, the indirect systems offer freeze protection.

 

Passive Systems

Passive systems circulate water or heat fluid through the heat-driven convection or heat pipes. The water goes through the heat pipe and absorbs the heat. The passive system cost less and the maintenance is low as well; however, the efficiency of the passive systems is lower than the active systems.

 

Active Systems:

The active systems have many pumps and controllers which make the systems more complex and expensive. The storage tank can be set lower than the collectors, which increases the freedom in the system design. Situating the tank under the collectors makes a better view and placing the tank in conditioned or semi-conditioned space could reduce the heat loss. In addition, the drainback tanks can be used. Overall, the whole systems are very efficient and a lot of controls over the systems are given.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: (A) Direct, Passive CHS system with tank above collector 

(B) Direct, Active system with pump and controller driven by a photo-voltaic panel

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2: (C)  Indirect, active system with heat exchange in tank

(D) Indirect, active drain back system with drain back reservoir

 

 

 

Typical Materials:

The main part of the solar hot water systems is the solar panel. The silicon solar cell on the solar panel is the main material that converts the sunlight into electricity. However, the silicon solar cell can have 18% efficiency. The other parts of the systems are basically aluminum glazing bars and pipes. 

 

 

Typical Uses:

 

​Residential:

The solar hot water systems are very commonly used for residential purposes. The residential solar hot water systems will supply the hot water generating and storing. The solar absorption panels are usually located at the roof of the building. The storage tanks are located inside the house or connect with the solar panel on the roof. The residential solar hot water systems saves a lot of electric or gas costs and it is very efficient. However, the solar hot water systems rely on the climate situation too much; therefore, usually the solar hot water systems combine with the electric or gas hot water systems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: Typical Residentail Solar Water Heating System

 

 

Industrial:

The uses of the solar hot water system in the industrial aspect are more limited than in the residential aspect because the industry needs too much energy to rely on the solar energy. The solar panels need a lot of spaces to place and the unstable climate is also a factor that limits the uses of the solar energy in the industrial aspect. However, the solar energy is very clean and it reduces a lot of cost on the electricity and gas. The maintenance and the replacement are cheap as well. The solar hot water systems are usually used in the pre-heat water system. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4: Industrial Rooftop Solar Water Heating System