Today we are going to talk to you, long and hard, about  solar thermal energy  –  what it isclassificationoperation , advantages and disadvantages .


When you finish reading this article, it is possible that you rethink the complete change of the installation of your house.



Thermal solar energy characteristics

Solar thermal or solar thermal energy is the one that means the capture and absorption of the heat emitted by the sun is used to heat water to be used in mechanical systems, for cooking, heating and cooling for machines that use heat instead of electricity and power. condition the environments.

Elements and description

Solar thermal energy uses collectors that capture the sun’s rays and absorb the energy they emit in the form of heat, through which a fluid is passed, which is commonly water, to which the heat is transferred, then where it is consumed.

The collectors can pass through and heats some tubes through which the liquid that must be heated passes. The tubes must be covered with black paint that absorbs heat much better and also keeps it longer.

The glass that covers the installation not only protects the collector but also generates a greenhouse effect that benefits the collector’s performance.

The elements that make up a solar collector are the following:

Cover:  Must be transparent, usually glass or special plastic, the function is to reduce heat loss and transmit energy with great efficiency.

Absorbing plate:  It is responsible for capturing the sun’s rays and absorbing heat and then transmitting it to the pipes. It must have a good absorption of heat and minimum thermal emission to reduce the loss of heat.

Pipes:  They can be welded or simply joined to the panel so that as much heat as possible can be transferred from the panel to the said pipes.

Air channel:  It can also be vacuum, it is a space between the plate and the cover, its function is to balance the heat loss by convection and high temperatures depending on its thickness.

Insulating layer:  The purpose of this layer is to cover the system to reduce heat losses.



As you can see, in the use of this type of energy can lose much of the heat between the characteristics of the components of a thermal system should be the ability to contain heat and reduce losses.

A practical use of a solar thermal system is to generate water for sanitary use where the water passes directly through the collectors but there are some problems in areas where the high concentration of salts ends up obstructing the conduits.


Basically it is to take advantage of the energy generated by the sun and convert it into heat , through some element that is usually air or water. However, there is also the option of converting this solar thermal energy into electricity.

The method is as simple as raising the temperature of water to more than 100º to evaporate, and thus generate electrical energy.


Solar thermal energy operation

The operation of thermal solar energy is as follows:

The principle of operation of a solar thermal installation is not too complicated: The solar panel captures the sun’s rays, thus absorbing its energy in the form of heat.

Through the solar panel we pass water so that part of the heat is transferred to the fluid that raises its temperature and is stored and brought to the point of dew.


Description of components and equipment

Solar collectors

The solar collector is the fundamental element of any solar thermal system. Its mission is to capture the solar energy incident and transmit it to the flow that flows through it.


The need for energy does not always coincide in time with the collection obtained from the sun, it is necessary to have an accumulation system that meets demand at times of little or no solar radiation.

Heat exchangers

The heat exchanger in a solar installation is placed when you want to transfer the heat from one fluid to another, without mixing them, thus separating the two circuits.

When it exists, it is responsible for transferring the energy absorbed by the collectors (which contain water with antifreeze when installed in the open) to the domestic water of the accumulator.

Circulation pumps

The circulation pumps are powered by an electric motor, capable of supplying the fluid with an amount of energy sufficient to transport the fluid through a circuit, overcoming the pressure losses therein.


The insulation is fundamental in a solar thermal installation to avoid heat losses to the outside.

Glass of expansion

Its function is to absorb the expansions of the fluid contained in a closed circuit, produced by increases in temperature. They can be open or closed. Thus, the expansion vessels will always be placed in closed circuits.

These are the main components of a thermal solar system. However, we will have more elements such as pipes, valves and accessories, purgers and deaerators, thermometers, thermostats or pressure gauges that will make the system work properly.

Watch the video and learn more about solar thermal energy

How can thermal energy be used?

The water  is  heated with  thermal energy  and then this water  can  be used for many applications. The domestic application par excellence for  solar  thermal energy  is the heating of water through thermal solar panels, with which  the water for domestic heating  is heated

Solar thermal system for domestic use

Obviously, a  solar thermal system for domestic use  is a tool that will help save energy and money to anyone who has it. For domestic use, one of the three types of solar thermal collectors available is needed to accumulate energy.

The type of collector to choose will depend on the purpose that we will give to the solar thermal system for domestic use.

  • Low temperature collector  – When you require temperatures below 65º
  • Average temperature collector –  When you require temperatures below 300º
  • High temperature collector  – When you require temperatures below 500º or you are looking to accumulate electricity.


What is the use of solar thermal energy? 

Solar thermal energy has many applications, these are some of the most developed:

  • In homes:  You can provide domestic hot water (DHW) in the home, heating, cooling and swimming pool heating.
  • In industrial facilities:  there are many industrial processes that require large quantities of hot water at temperature ranges that can be supplied by solar installations.
  • In the agricultural sector:  For heating greenhouses and farms, heating water from fish farms, cleaning slaughterhouses and fish markets, etc.

There are subsidies (for facilities that do not have to comply with the CTE) and financing at low interest, increasing the profitability of these facilities.

Systems that form an installation of thermal solar energy

A solar thermal system is a complex machinery, so you should know the systems that form a solar thermal installation .

Solar radiation collection system 



The solar radiation collection system is what make up the solar collectors or collectors . They are the ones who initiate the process, collecting solar energy to become thermal energy.

Therefore, the collectors must be connected and can be of various types, although the most common is the  flat solar collector .

It can generate temperatures of up to 60º at a ridiculous price. It is, therefore, a low temperature thermal solar plant.

Other systems for capturing solar radiation can be the 

  • Non-glazed  (used to heat water from swimming pools or spas);
  • Vacuum solar collectors ;
  • Concentration collectors  (used in large installations)
  • Solar thermal collectors with sun tracking systems  (rotate as the sun moves throughout the day, to gain as much energy as possible).



Thermal solar energy accumulation system 

The  accumulation system of solar thermal energy  is the element that accumulates the heat energy in a warehouse, ready to be used when required.

The heated water arrives directly at the tap, normally. Of course, in some facilities, if the sun is not out, it may take a while to start going hot.

Obviously, this system of accumulation of solar thermal energy should have a  size according to the use . If it is for domestic use, a 60 liter tank is enough. If it is for a pool, an irrigation or any industrial purpose, the deposit must be much larger.



Thermal solar energy distribution system

The  solar thermal distribution system  is the next step in the mechanism. It is responsible for bringing the thermal energy of the collector to the area where it wants to be used. That is to say, in the distribution system of solar thermal energy they are included from the pipes, to the purgers, passing through the controllers.

This system also includes the emergency system, which will jump if it fails. That is, the boiler or the radiator. And is that  if solar radiation is missing at some point , we must have a backup plan.



Convectional energy support systems

Finally,  conventional energy support systems  are those that support when there is no solar radiation or when the demand is higher than expected. These conventional energy support systems use  fuelelectricity or natural gas .

The usual thing is that a solar thermal system for domestic use, covers 80-85% of the energy demand of a home . If the area receives a greater than average amount of sunshine, this percentage can touch 95%.

The rest is covered by conventional energy support systems. Of course, during autumn and winter, this percentage can go down to 70% due to the absence of sun on many occasions. So things, reaching 80% on average is a triumph.

Thermal solar energy advantages and disadvantages

Finally, we analyze the  advantages and disadvantages of a solar thermal system . Everything for you to shuffle if it deserves or not worth launching for self-consumption.


Read more about Solar thermal energy to heat water

V entajas of a thermal solar system

The  advantages of a thermal solar system  are:

    • It does not pollute  – It is a clean energy that leaves fossil fuels in diapers.
    • Unlimited  – The sun is an inexhaustible source of renewable energy. A luxury.
    • It reaches everywhere  – In the end, he only arrives where the power lines do not reach.
    • Minimal  maintenance – Maintenance is simple and almost non-existent
    • Savings  – Not only energy, but also economic. In less than three years you will have it amortized, because you will only make the initial investment.
    • Space  – If you put the sensors on the roof, you do not need to look for a place.



Disadvantages of a thermal solar system

The  disadvantages of a thermal solar system  are:

    • Radiation  – Radiation levels are very variable, and that scares.
    • Investment  – Maintenance is minimal but the initial investment is important. Now, a family can recover their investment in no more than seven years.
    • Aesthetics  – Man does not live only from solar panels. There are tremendous collection systems, decorative and according to what you look for your home. Yes, solar panels are still the best sellers.
    • Space  – If the goal is large-scale, an immense amount of terrain is needed for installation. Not only is it complicated, but it goes a lot of price.

Thermal and photovoltaic solar energy

Solar thermal energy VS photovoltaic energy?


It is important to understand that solar thermal technology   is not the same as that of a photovoltaic energy system  . The generation of  solar thermal electric energy  concentrates sunlight to generate heat, in addition to the heat used to run the thermal engine, which rotates a generator to produce electricity. On the contrary,  photovoltaic solar energy  directly converts sunlight into electricity.

As solar energy has had a rapid growth within the sector of renewable energy sources, important attention has been paid, both publicly and privately. From Ainfar we wanted to consider which of the available solar technologies, that is, whether  solar thermal or photovoltaic energy is more profitable and efficient.

Representative characteristics of solar thermal energy and photovoltaic energy

The  photovoltaic and solar thermal  are the two solar technologies established. The  photovoltaics  uses a devised by semiconductors to convert sunlight directly into electricity system.

The  photovoltaics , therefore, only works when the sun is shining, and must be accompanied by other power generating mechanisms to ensure a steady supply of electricity.

Concentrated sunlight is used either directly as a heat source, as in solar water heating, or to drive a heat cycle, like that of an engine.

In addition, since  solar thermal energy  is produced directly with heat, it can store thermal energy from various media. Some plants, in fact, can store enough energy for about 8 hours without the need for sunlight; So, solar thermal energy can potentially generate energy 24 hours a day.

However,  photovoltaic energy  is becoming a very popular source of energy at the public level because the capacity to generate energy through a photovoltaic system   has greatly improved compared to the generation of  solar thermal energy  for large installations.

Skinny spots of solar energy

Solar energy is one of the most expensive sources of renewable energy available compared to other sources of energy. However, currently, there is little price difference between  photovoltaic  and solar thermal energy ; But,  photovoltaic energy  can become something more affordable.

The trend, therefore, is that prices will decrease over time, especially by government actions that support the green commitment, as Ainfar does. In addition, as the  photovoltaic components  have entered a clear and direct industrial phase, clearly benefiting the entrepreneur, the industries also do, little by little, to support initiatives such as the consumption of renewable energy.

What do we conclude, then, about solar thermal and photovoltaic energy?

Although the technological differences are debatable, it is clear that both technologies are somewhat more expensive than other sources of renewable energy. But, on the one hand,  solar thermal energy  has the advantage that it can be stored and  photovoltaics  that are profitable for large installations.

The future is very sweet in the face of expectations like this one and it remains optimistic: it is foreseen that  photovoltaic energy  will be able to supply electricity to almost two thirds of the world population in less than 20 years, according to data provided by Greenpeace. Other studies reveal that within 100 years maximum boom will occur with respect to this type of energy and, practically, all the energy we consume will be solar.

Thermal solar energy as you get 

Thermal solar energy:  its main component is the collector, through which circulates a fluid that absorbs the energy radiated from the sun.

The high temperature thermal solar systems refer to large installations where the main element is a paraboloid tower, or a field of heliostats that concentrate solar radiation in a tower.

Thermal solar energy examples 

The  thermal energy , also known as  heat energy  or  heat is manifesting itself as heat. It is, however, a product of the movement or vibration of atoms, so it is a manifestation of the  internal energy of  the system, which is nothing more than the accumulated kinetic energy of the particles.

This type of energy is measured, like the others, in joules ( J ), according to the international system, although it is also usual to talk about calories: 4.18 joules, the amount of caloric energy needed to raise a gram of one degree of a degree Water.

The amount of thermal energy in a system, as will be assumed, has directly to do with the temperature exhibited by it. Thus, the  more thermal energy (heat) we introduce to a container with water , for example, the higher its temperature will rise, until reaching the necessary for a phase change: water evaporates and goes from liquid to gaseous.

Transmission of thermal energy

Thermal or caloric energy  can be transmitted from one medium to another or from one body to another  in three specific ways:

  • Transmission of heat by radiation. In this first case the thermal energy is displaced by electromagnetic waves, as is the case with the sun’s energy. It is also what happens when we turn on the heating: the air is radiated from heat and the temperature rises.
  • Heat transmission by conduction. This case occurs when a hot body comes into direct physical contact with a cooler body, resulting in heat being transmitted and temperatures being equated. This does not happen if the initial temperature is the same.
  • Transmission of heat by convection . This is the name given to the displacement of hot particles in a colder environment, such as wind: the air that moves contains particles at a higher temperature that make us perceive the whole as hot air.

Examples of thermal energy

  1. Boil the water . As we said earlier, by introducing heat from a flame into a container of water, we can raise the temperature by multiplying the thermal energy of the system (its internal energy) to force the water to a phase change ( evaporation ). The same happens with ice: if we extract it from the freezer, the heat from the environment will radiate towards the solid until it becomes liquid water again.
  2. Fireplaces . A chimney is only a place where a  constant organic matter combustion is maintained  so that the heat energy produced by the fire radiates to the joint rooms and keeps the house warm.
  3. The heaters. Useful to maintain water at an ideal temperature, electric heaters operate based on a set of metallic resistances that transform  electrical  energy into heat energy, increasing the temperature of the water to the proper point.
  4. The sun . The largest source of thermal energy available to us is the sun, whose constant combustion processes radiate enormous amounts of heat and light to the universe that surrounds it. Cold-blooded animals take advantage of this energy source, for example, by exposing themselves to sunlight to warm their body.
  5. The atomic bomb . The atomic bombs and their pacific version, the nuclear power plants, do nothing but produce atomic reactions in chain (controlled in the case of power plants and without control in the case of pumps) to generate large amounts of heat energy from the alteration of the fundamental energies of the  atom .
  6. The homemade thermos . A thermos filled with hot coffee, for example, is ideal for observing the caloric energy that radiates (if we put our hands close) and the energy that is conserved (if we drink a cup). This happens because the thermo material prevents or reduces the heat radiation considerably and preserves the temperature of the liquid.
  7. The cooking ovens . The ovens work from the concentration of thermal energy to increase the temperature and exercise changes in food (cooking). This energy comes from the  transformation of  electrical energy (by resistances) or from the continuous combustion of natural gas.
  8. The human body . The chemical reactions that take place inside our body, including our own breathing, generate a quantity of thermal energy that keeps our body temperature around 37 ° C. That energy is perceptible and transmissible, in fact the coats work preventing the escape of that heat through the surface of the skin.
  9. The combustion of organic matter . Burning wood, coal or other flammable organic substances is a method of obtaining thermal energy usual in the history of mankind. In fact, today that heat is used to boil water which in turn mobilizes the turbines that generate electricity.
  10. The rubbing of the surfaces . The  kinetic energy  and friction can often become caloric energy, as happens when we repeatedly rub our bare hands and feel how friction raises the temperature. This movement increases the thermal energy and can then be transmitted by contact, if we apply freshly rubbed hands on another part of the body, as in the massages.
  11. A running engine . The internal combustion engines generate thermal energy in abundance, since the controlled explosion in its interior and the electric flow of many of its parts, as well as the constant movement of the pistons, transform into heat all the energy they handle. This thermal energy can be perceived by placing your hands on the hood when the car has been in operation.
  12. An incandescent light bulb . The passage of electricity in the filament of an incandescent bulb produces light (yellow), but also produces heat: that’s why it costs to change a bulb that was on for a long time, its surface has accumulated thermal energy that radiates the passage of electrons.
  13. The melting of metals . In metallurgy, the metallic solids that are worked are exposed to very high temperatures in large smelting furnaces. This is to increase its thermal energy to the point of forcing, as in the water example, a phase change. Thus, the metal becomes liquid and can be mixed or molded. During the time it takes to cool and solidify again, the metal will radiate the surplus of thermal energy to the environment.
  14. The environmental water vapor . In places with high environmental humidity, in which the air is loaded with water particles, the heat is perceived much more than in the drier places, giving rise to the elevated thermal sensation. This is because the water in suspension is heated and by  convection  of the thermal energy we perceive the environment at a higher temperature than it is.
  15. The thermal waters . Under the earth’s crust there is water in deposits subjected to high pressures and high temperatures, which when springing to the surface becomes thermal waters. These liquids have such thermal energy that they can melt frozen layers when they reach the surface, causing large jets of steam (geysers).


Geysers of Yellowstone Park in the USA.

Low temperature thermal solar energy


Low-temperature solar thermal installations are considered those installations of solar thermal energy that provide useful heat at temperatures below 65 ° C through solar energy.

A solar thermal installation of low temperature is formed by solar collectors, two water circuits (primary and secondary), heat exchanger, accumulator, expansion vessel and pipes.

The circulation of water inside the circuits can be obtained by thermosiphon, taking advantage of the density difference of the water at different temperatures or by means of a circulation pump.

Although with a circulation pump an external contribution of electrical energy is needed.

Solar thermal sensors capture solar radiation to transform it into heat energy or heat. There are different types of solar thermal collectors, currently we know those with flat plates, those with vacuum tubes and absorber sensors without protection or isolation.

The solar thermal collectors are composed of the following elements:

  • Cover: It must be a transaprente material, usually it is glass, but there are certain plastics that can also be used with the advantage of being cheaper and more manageable. The function of the cover is to minimize the heat losses by convection and radiation and therefore must have a solar transmittance as high as possible.
  • Air channel: It is a space that separates the cover of the absorbent plate and may be empty or not. To calculate its thickness, it is necessary to balance the convection losses and the high temperatures that can be produced if it is too narrow.
  • Absorbent plate: The absorbent plate is the element that absorbs solar energy and transmits it to the liquid that circulates through the pipes. The main characteristic of the absorbing plate is that it has to have a great solar absorption and a reduced thermal emission. To meet this requirement, combined materials are used to obtain the best absorption / emission ratio.
  • Pipes or ducts: The tubes are touching (sometimes welded) the absorbent plate to maximize the exchange of heat energy by thermal conduction. The liquid that is heated will circulate through the tubes and transport the heat to the accumulation tank.
  • Insulating layer: The purpose of the insulating layer is to cover the system to avoid and avoid thermal losses. In order for the insulation to be the best possible, the insulating material must have a low thermal conductivity.

What is a thermal solar plant?

A solar thermal power plant  or solar thermal power  plant is an industrial installation in which, from the heating of a flow by solar radiation   and its use in a conventional thermodynamic cycle, the power needed to move an alternator to generate electrical power is produced as in to central …