What Is The Working Principle Of Solar Water Heaters?

- Dec 05, 2020-

Sunlight passes through the first layer of glass of the heat-absorbing tube and shines on the black heat-absorbing layer of the second layer of glass, which absorbs the heat of solar energy. Since the two layers of glass are vacuum insulated, heat transfer will be greatly reduced (Radiation heat transfer still exists, but there is no heat conduction and heat convection), most of the heat can only be transferred to the water in the glass tube, so that the water in the glass tube is heated, and the heated water moves up along the heating surface of the glass tube. Into the heat preservation water storage bucket, the relatively low temperature water in the bucket enters the glass tube along the backlight surface of the glass tube for supplementation, and this continuous circulation makes the water in the heat preservation water storage bucket continue to be heated to achieve the purpose of hot water.

Endothermic process

When the evacuated tube water heater absorbs heat, solar radiation passes through the outer tube of the evacuated tube, is absorbed by the heat-collecting coating and is transferred to the water in the tube along the inner tube wall. After the water in the tube absorbs heat, the temperature rises, the specific gravity decreases and rises, forming an upward power, forming a thermosyphon system. As the hot water continues to move up and is stored in the upper part of the water storage tank, at the same time, the lower temperature water is continuously replenished along the other side of the pipe in such a cycle, and finally the whole tank of water rises to a certain temperature.

Flat-plate water heaters are generally split-type water heaters. The medium circulates naturally in the heat collecting plate due to thermosyphon, and the heat of the solar radiation on the heat collecting plate is transmitted to the water tank in time. The heat exchange (jacket or coil) in the water tank transfers The heat is transferred to the cold water. The medium can also be circulated through the pump to achieve heat transfer.

Circulation pipeline

Domestic solar water heaters usually work in a natural circulation mode, without external power. The vacuum tube solar water heater is a direct plug-in structure, and the hot water is powered by gravity. Flat-plate solar water heaters are powered by the pressure of tap water (called top water). The solar central heating system adopts pump circulation. Due to the small heat collection area of solar water heaters, pipe circulation is generally not used in consideration of heat loss.

Components of solar water heater


The heat collecting element in the system. Its function is equivalent to the electric heating tube in an electric water heater. Unlike electric water heaters and gas water heaters, solar collectors use the radiant heat of the sun, so the heating time can only be when the solar radiation reaches a certain value.

At present, the most common one in the Chinese market is the all-glass solar vacuum heat collection tube. The structure is divided into outer tube and inner tube, and the outer wall of the inner tube is plated with selective absorption coating. The heat-collecting panel of the flat-plate collector is plated with black chrome and other heat-absorbing films, and the metal tube is welded on the collector plate. The cost of flat-plate collectors is slightly higher than that of evacuated tube collectors. Flat-plate collectors have shown an upward trend in recent years , Especially in the balcony solar water heater of high-rise residential buildings has unique advantages. The all-glass solar heat collection vacuum tube is generally made of high borosilicate 3.3 extra hard glass, and the selective heat absorption film adopts the vacuum sputtering selective coating process.

Insulation water tank

A container for storing hot water. The hot water collected through the heat collection tube must be stored in the heat preservation water tank to prevent heat loss. The capacity of a solar water heater refers to the water capacity that can be used in the water heater, excluding the capacity that cannot be used in the vacuum tube. For pressurized solar water heaters, its capacity refers to the capacity of the medium capable of heat exchange.

The thermal insulation water tank of solar water heater is composed of three parts: inner tank, thermal insulation layer and water tank shell.

The tank liner is an important part of storing hot water, and its material strength and corrosion resistance are very important. There are materials such as stainless steel and enamel on the market. The quality of the insulation material of the insulation layer is directly related to the insulation effect, which is especially important in the cold season. The better heat preservation method is the heat preservation of polyurethane integral foaming process. The outer shell is generally color steel plate, aluminized zinc plate or stainless steel plate.

The heat preservation water tank requires good heat preservation effect, corrosion resistance and clean water quality.


Shelves that support the collector and the heat preservation water tank. It requires firm structure, high stability, wind and snow resistance, aging resistance, and no rust. The material is generally stainless steel, aluminum alloy or steel sprayed plastic.

Connect the pipe

The solar water heater first enters the cold water into the hot water storage tank, and then transfers the heat to the heat preservation water tank through the collector. The hot water storage tank is connected with the indoor cold and hot water pipelines, so that the whole system forms a closed loop. Reasonable design and correct connection of solar energy pipelines are critical to whether the solar energy system can achieve the best working condition. Solar energy pipelines must be thermally insulated. In cold areas in the north, heating cables need to be laid on the outer wall of the pipeline to ensure that users can use solar hot water in cold winter.

Control unit

Generally, domestic solar water heaters need to operate automatically or semi-automatically, and the control system is indispensable. Commonly used controllers are automatic water supply, full water shutoff and display of water temperature and water level. Solar water heaters with electric auxiliary heating also have leakage protection and anti-dry burning. Features. There are intelligent solar water heaters controlled by mobile phone text messages on the market, which have the functions of water temperature and water level query, fault alarm, start water supply, close water supply, and start electric heating, which is convenient for users.

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