Solar water heater helps in heating water with the help of solar energy for residential, commercial, and industrial purposes. Basically a solar water collector that is placed in a wall facing the sun helps in heating the cold water with the help of the rays of the sun. The heater is available in two types i.e. active and passive. The collectors consist of a box that is insulated and has a black painted glass cover, a solar metal absorber that is flat and is fastened to wires made of copper. Heat is stored in a separate water tank with an outlet and inlet which is attached out to the collector. Passive collectors make use of electricity to produce hot water where there is no access to sunlight and the temperature is too cold. Now let’s talk in brief about both these systems.
There are two kinds of primary systems namely
Batch: it is a tank inside a solar collector without any tubes. The water heats inside and either the gravity or the tendency of the hot water to rise, moves the water upwards and the water reaches the home pipes.
Thermosiphon: In this the water collector and solar system both are separate. Cold water moves through the solar collector tubes and then natural convection pumps which results in hot water in the storage tank. That water then travels to home pipes.
Direct: This system makes use of pumps. The water moves from solar collectors to storage tank with the help of electrical pumps.
Indirect: In this system the solar collectors heat the heat transfer fluid and not the water. The fluid then flows through a sealed piping of a heat exchanger which is full of water. The water absorbs the heat from the fluid and then is pumped inside the storage tank.
Drainback: This is similar to the indirect method. The only difference here however is that it uses distilled water as the heat transfer fluid. It has a separate tank for the distilled water. Pumping out the heat transfer liquid into a separate tank makes it perfect for use during cool climates.
By now you might have understood the variation in the working of the solar water heaters on the basis of collector classifications and the active and passive distinctions. To make it easy for you, I would be explaining the working of a basic solar water heater. This would help you to understand the common mechanisms in a solar water heater. The key mechanisms are as follows:
Heating: The collector is exposed to sunlight. The radiation from the sun passes from the glass top into the collector, here it is absorbed by the heat absorbing material. Thus, the radiation from the sun is converted into heat and the water inside the collector gets heated.
Movement: Now the water is heated and it needs to be transferred to the storage tank. Gravity or the convection can play a decisive role in the movement of the water.
Gravity: If the storage tank is situated at a lower level than the collector, then the heated water will be transferred to the tank under the influence of gravity.
Convection: It is the phenomenon by which the water tends to rise after heating. If the water tank is situated at a level higher than the collector, then the water rises to the tank through convection.
Storage and Use: Storage tanks are used to segregate the water from the collector. The tanks should ideally be kept in a conditioned environment to avoid the cooling of water due to external atmosphere. This water can be used by connecting pipes to the tanks. In a geographical region with ample sunlight, a solar water heater can meet 80-90% of the household requirements.
Source: Peak Solar