What are Solar thermal collectors: some facts to know.

Solar thermal collectors are devices, that arrest the solar radiations from the sun’s rays as heat. It is usually referred to as a device for a solar water heater for domestic uses and space heating or cooling.

What are Solar thermal collectors?

Solar thermal collectors are devices, that arrest the solar radiations from the sun’s rays as heat. It is usually referred to as a device for a solar water heater for domestic uses and space heating or cooling. However, it may also be referred to as the bigger installations for generating power including parabolic troughs, parabolic dishes, power towers etc.

Solar thermal collectors include many components and types manufactured as per the requirements.

Components of Solar thermal collectors:

A solar thermal collector consists of some of the important components for proper functioning. They include;

Solar radiation absorbing element or arrestor:

Solar radiation-absorbing element or arrestor or collector is normally a flat dark coloured plate or tube that absorbs solar energy.


Such an item comes with a transparent cover, generally made out of glass materials. The cover allows the solar radiation to pass through it to reach the absorbing element or absorber and reduce heat loss from it.

A heat transfer fluid(HTF):

HTF may be liquid or gas that transfers heat from one absorber to the storage tank or heat exchanger. The application of a heat transfer fluid is required in the process where maintenance of a particular temperature is needed. HTF is also referred to as heat pump antifreeze, heat pump fluid, glycol, brine etc. The low-temperature heat fluids are salt brines, hydrocarbon and silicon oils. However, Therminol66 is considered the world’s most popular high-temperature, liquid-phase heat transfer fluid.

Insulated housing:

The absorber, cover and HTF all are connected to insulated housing. Such installation may have glazed to allow solar radiation to enter but minimise the heat loss to a great extent. The insulation materials may be fibreglass, cellulose, natural fibres etc.

Types of Solar thermal collectors:

Many types of solar thermal collectors are now available which include, as follows;

Flat plate solar collectors:

It is the most common type of solar collector developed in 1950. The objective of the innovation was to use solar energy for providing hot water requirements for the household for domestic use. In such a device, water is heated when it passes through the dark/black flat plate under a transparent cover before it is returned to an insulated hot water storage cylinder. The flat plate can occupy more area because of its exposed surface area to solar radiation. Further, the HTF is circulated through copper or silicon tubes fitted within the flat plate.

Image of a flat solar collector
Image of a flat solar collector

Evacuated tube solar collectors:

Such installation is made up of insulated glass tubes, containing copper pipes within it. It is designed in such a way that the collector shall remain always perpendicular to the sun’s rays. This device provides high temperature, as the vacuum within the evacuated tube is designed to reduce convection and conduction heat losses. The water is heated in the collector before it is passed to the storage tank through a pipe. Evacuated tube solar collector is very useful in colder region of the world and the most efficient heating system but more expensive than Flat plate solar collectors. The thermal energy generation efficiency is considered at 70%.

Parabolic trough:

A parabolic trough is a type of solar thermal collector, where long and curved mirrors are arranged in such a manner, that reflects the concentrated solar radiation on an insulated tube or a heat pipe placed in the focal point. The generated heat is transferred to the boilers in the solar power plant for the production of power. It has advantages over Photovoltaic cells, as a parabolic trough is cost-effective and requires less area than PV cells.

parabolic trough solar thermal collector image.
Image of a parabolic trough thermal collector.

Parabolic dish:

The parabolic dish is a type of solar thermal collector basically used in solar power stations. In such a system, a few parabolic dishes are used to concentrate solar energy at a focal point. The dishes are fitted into the system in such a way that maximum radiation can be absorbed and losses are minimised.

Power tower solar collector:

The power tower solar collector is a setup to receive the focussed solar radiations. It is really a big tower fenced by tracing mirrors, known as heliostats for which it is also referred to as a heliostats power plant. Further, as the tower is stationed at the centre of the establishment, it is also called a central tower power plant.

The mirrors are movable and arranged to track the sunlight, collect it and transfer the same to the receiver at the top of the tower. The thermal energy is then transferred to the power plant to generate electricity. Such installations cover large areas at a relatively low cost against traditional solar cells.

Purposes of solar thermal collector:

The solar thermal collector mainly serves three purposes;

  • Heating the water: It uses solar radiation to heat a fluid or water directly. It serves the purpose of heating pool water and domestic hot water(DHW).
  • Cooling: It can be used for cooling commercial buildings such as central air conditioning systems.
  • Production of electricity: The thermal collectors in large power plants can produce electricity in huge quantities in a commercial manner. Parabolic trough, parabolic disk and Power tower solar collectors are some examples of thermal collectors, that produce electricity.

Solar collectors or solar cells which are better?

Solar collectors need more attention for their maintenance and cost-effectiveness. It is perfect for households to get domestic hot water but not electricity. The generation of electricity depends on weather conditions and large establishments. It may be feasible commercially.

On the other hand, solar cells or solar panels are more expensive but an assured source of green energy throughout the year for a longer period with lesser maintenance. Useful for domestic households, street lighting, and commercial buildings for energy needs. Further, PV cells can convert solar radiation or solar energy into electricity directly.

Bottom line:

The time has come to focus on eco-friendly green energy. Solar energy is one of the best solutions for the energy needs of domestic households and commercial establishments. To encounter the greenhouse effects, the generation of green energy is the only solution. We may see our energy future in solar collectors and solar cells.

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