Know more about solar thermal collector

Sun is the biggest and the most abundant form of energy source in the universe. Energy generated in the core of the sun can sustain this universe for billions of years to come. All of the energy stored under the surface of the earth is solar. Just like solar panels convert solar radiation directly into electricity, solar water heaters use heat from the sun into heating water. It ensures that no energy is lost while doing multiple conversion of energy from one form to another. For example, in the running of a car using petrol or diesel, chemical energy is converted into heat, which gets converted to mechanical energy of the shaft of the internal combustion engine. There is loss of energy, therefore decreased energy efficiency as a lot of energy gets wasted in the form of heat loss, friction, resistance etc. As the heat from this is captured directly by a solar thermal collector in a water heater, the whole process is much more efficient.

What are solar thermal collectors?

Solar thermal collectors collect heat by absorbing sunlight. It is installed in solar water heaters, solar parabolic troughs and solar towers etc. It has the aperture area that receives the solar radiation and the absorber area which absorbs the radiation. Depending on the relative size of the two, solar thermal collectors are of two types

Concentrating

In concentrating solar thermal collectors, the aperture area is larger than the absorption area. It helps in the concentration of solar heat, increasing its intensity. Common examples include concave mirrors where radiation is concentrated to an object or metal located at the focal point. Due to the movement of the sun, concentrating collectors need to track the sun to improve the concentration of heat. Therefore it is also called active collectors. It is commonly used in a concentrated solar power plant where heat gets transferred to a heat transfer fluid which helps to drive a turbine for generating electricity.

Non-Concentrating

The aperture area is roughly the same as that of the absorption area. Metal plates are painted with dark paint to maximize the absorption of heat. It is installed in commercial, industrial and residential places for space heating.

Solar thermal collectors are used extensively in solar water heaters. It is mainly of two types: flat plate and evacuated tube collector. Both are non concentrating used to capture direct and diffused sunlight to circulate fluids and heat water in the process.

Flat plate collectors

It consists of a flat absorber plate with typically black enamel paint to increase the absorption of heat. The plate is enclosed with a transparent covering on top to allow the transmission of solar energy. All the sides and back of the enclosure are insulated to avoid any heat loss. A heat transfer fluid is passed to the absorber’s fluid passway taking away all the heat to the heat exchanger. This heat exchanger heats the water. Hot water is then stored in an insulated water tank. Flat plate collector water heaters are usually directed at the sun to increase the availability of sunlight. In tropical countries, heat exchange fluid is usually water. In climatic conditions where temperature freezes down to zero, antifreeze liquid or a mixture of antifreeze liquid along with water is used. Flat plate collector solar water heater is one of the most commonly preferred type of water heater in Europe.

Next-generation flat plate collectors are much more efficient with an anti-reflective coating on top of the enclosure cover. It increases transparency, making way for much more sunlight. The absorber is coated with a specialized material that increases the absorption of the visible spectrum coupled with a low emittance of infrared radiation. It reduces the blackbody radiation most hot bodies have to undergo.

Evacuated tube collector

It uses a glass tube around the absorber with a high vacuum inside it. Vacuum around the absorber reduces the loss of heat by convection and conduction, achieving greater energy conversion efficiency. Absorbers inside the vacuum tube can be either metallic, as in the case of a flat plate collector or concentric glass tube acting as an absorber. It is known as the Sydney tube. Heat exchange fluid flows inside the Sydney tube exchanges heat with the heat pipe reaching inside. Like the flat plate collector absorber, the Sydney tube is insulated to protect the flow of heat and increase the transfer of sunlight to the absorber. Evacuated tube collectors are more complex than flat plate ones increasing the price significantly. But there are situations where evacuated ones are much more desirable to use.

To know more about solar panels and water heater installation, contact Grand Agency or visit https://grandagency.in/ for more information.