How Do Solar Water Heaters Work?

Structurally, solar water heaters are most often made in a structure, which is commonly called a flat solar collector. We already know that heat from the absorber can be removed directly by the heat carrier or transferred through heat pipes; therefore, we will not focus on this. We take a certain collector; how to increase its capacity? There is only one way – to increase the area. Therefore, the capacity of our solar water heater will depend on its type and area. There is such a thing as the nominal efficiency of the installation. The absorbers themselves can have an absorption efficiency of up to 98%, but there will still be losses in real installations.

They are associated with incomplete transparent glass or plastic, reflection and others. For a leaky but well-insulated collector, it is 72-75%. For a vacuum collector with heat pipes, it is 60-65%; and for a plastic collector, 50-60%. In a vacuum collector, solar energy is lost as it passes through a system that provides a vacuum, as it travels from an absorber to heat pipes, etc., so the efficiency is lower. And in practice, when such systems operate at elevated temperatures, vacuum systems may even be less efficient. But now, when the ambient temperature is lower,

Solar Water Heater

Flat solar collector

 The actual efficiency decreases by an amount proportional to the difference between the temperatures of the coolant and the environment and multiplied by a factor determined by the type of collector. For a leaky collector, it is 3-5. For a vacuum one, 0.7-1.1, and a plastic one can reach 80. The value of the coefficients tells us that the plastic one will not work at low temperatures, especially negative ones. And a leaky one can and will work, but a vacuum one will be much more efficient. 

Water heater with two collectors

 The operating temperature in open systems, the water that we then use, is usually 30-70 degrees. A special heat carrier is usually used in closed systems, its temperature is higher, and hot water is heated in a heat exchanger tank. We cannot turn off the water heater; therefore, with a small water intake and maximum solar irradiation, they can reach 200 degrees in unsealed collectors and 300 degrees in vacuum ones.

Way to get energy from the sun

Saw solar collectors at the construction and architecture exhibition. In winter, they say that the collector can be heated to the temperature required for heating the premises in Siberia. Interested in this information, I studied the topic of heating water using a solar collector and a rechargeable battery available here.

A solar water heater is a device for collecting solar energy in a coolant. At the moment, this is the most efficient way to obtain alternative energy.

Solar collectors are direct action for water heating.

They represent a glass panel, inside of which black material is applied, and water is pumped. The sun’s light passes through the glass, hits the black material, and heats it; the heat is transferred to the water. Warm water can be used for a hot water supply. A direct solar collector is sometimes referred to as a solar water heater. I saw these in Turkey near the beach.

More versatile are solar vacuum collectors.

They can be used even in winter. The solar collector of the vacuum type consists of glass tubes. Inside each pipe, there is another pipe, and between them, there is a vacuum (like in a thermos). It is the vacuum that prevents the release of heat at negative temperatures. The inner tube has a special coating that absorbs the solar heat. A copper tube is inserted inside the inner glass tube, into which Freon is pumped. Freon heats up and turns into steam. The steam rises, condenses, giving off heat to the collector, and the condensate goes down the tube. The collector transfers heat to the antifreeze, which is transferred through the pipes to the heat exchanger and gives up its heat to the water. Vacuum collectors allow you to heat water up to 100 degrees, even winter. In everyday life, solar collectors are used for space heating and a hot water supply.

Can hail damage solar water geysers in winter?

Concerns about hail are in vain for owners of high-quality tubular and flat collectors because:

  • High-quality tubes are made of tempered glass (in some cases with additional reinforcement), the strength of which is an order of magnitude higher than usual;
  • Transparent panels of flat models are made of reinforced glass or composite materials – plastic, fiberglass (specific protection parameters depend on the manufacturer).

Such systems can easily withstand a hail of varying intensity and magnitude, up to an average rainfall diameter of 3-5 cm. Many manufacturers show videos of firing metal or stone balls to simulate hail on their collectors as proof of strength. 

How does a solar water geyser work in cold weather?

The second serious factor affecting the efficiency of solar systems is the ambient temperature, but the decrease in efficiency in frost is typical only for flat collectors. This is because the heating agent tube network is in contact with the outer panel through which the heat is escaping. Many manufacturers have begun installing an insulating layer between the transparent panel and the tubes to reduce this effect. 

A vacuum is formed between the tube with the heating agent and the outer transparent casing in tubular ones, which is a poor heat conductor. Therefore, tubular models demonstrate a minimum heat loss even in frosty conditions. 

It is worth noting here that frost can play a cruel joke with tubular collectors at high humidity and tighten the outer glass casing with frost, reducing the number of penetrating sunlight. But you should not be afraid of such situations, because: 

  1. The transparency of frost is several orders of magnitude higher than that of snow, and it has a very insignificant effect on productivity.
  2. The frost leaves in a few hours of sunny weather, so if a bright sun appears in the sky, it will quickly melt it, and if there is no sun, then the collector’s efficiency will decrease, regardless of the frozen layer. 
Solar Water Geyser

Do you need a solar water geyser in winter?

To summarize the influence of weather factors in the conditions of our climatic zone.

  • The number of sunny days in winter drops sharply;
  • The collector surface can be covered with snow or frost; 
  • Flat models will give off a significant amount of heat through the outer panels, especially in severe frosts.

However, in the cold season, we can note that.

  • Collectors easily tolerate temperature extremes and precipitation;
  • It is difficult to damage them with hail or ice;
  • You do not need to pay for the heat received;
  • With enough sun, the efficiency of the system drops slightly.

Considering that flat collectors have a mechanism for self-cleaning from snow, their efficiency is influenced only by the number of sunny days and the ambient temperature. In general, such a system will heat water by the sun, but its efficiency in winter drops by 3-4 times.

Suppose it is possible to calculate the required power reserve for hot water supply and install additional models. In that case, solar water geyser in heating systems is possible only as an additional source of water heating. 

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