HOW SOLAR THERMAL ENERGY WORKS

Thermal solar energy is another clean way to take advantage of sunlight,

HOW DOES THE LOW TEMPERATURE THERMAL SOLAR ENERGY WORK?

For several years, we have heard about solar thermal energy, we have installed solar panels on the roofs of buildings, single-family homes, hotels, etc. considering it to clean and efficient energy.

In this article we will explain how it works, what elements are needed and what we must take into account to get the most out of it. Likewise, we will indicate the advantages of this type of energy in terms of its profitability and energy efficiency.

What is solar thermal energy?

To get an idea, we indicate that the percentage of energy of domestic hot water in a home or hospital corresponds to 20%. In hotels, depending on the type of establishment, it would be around 23%.

Therefore, it is one of the systems where we can reduce costs, with the consequent energy saving and reduction of CO2 emissions. Indicate also that solar thermal energy is not only used for the use in taps and showers, but can be used as support for heating swimming pools, heating, preheating, etc.

But, what does Thermal Solar Energy consist of? Well, the answer is simple. If we have an inexhaustible source of energy, such as solar radiation, and with it we can heat a fluid without the use of any fuel and take advantage of it for different uses, the idea seems great, right?

Therefore, one of the key words in solar thermal energy is the use of the sun’s energy.

Once we know that we can take advantage of this energy, we need elements that allow us to capture it, transport it, transfer it and accumulate it.

How does solar thermal energy work?

To know how solar thermal energy works we must know the components of the thermal system but basically the principle of operation is as follows:

The solar collectors absorb sunlight and heat a liquid or fluid, this liquid circulates through an internal circuit in a water tank transferring this heat to the water by heating it.

What are the components of a solar thermal installation?

The basic elements that intervene in an installation of this type are the following:

Collectors or solar collectors 

They allow us to capture solar radiation and heat the heat transfer fluid circulating through them. There are different types and with different yields.

Hydraulic circuit

Logically, we will need a circuit to transport the water heated in the collectors. This circuit will be closed (most usual installations).

Therefore, we will talk about output circuits (panel output) and return (panel input). We can make a simile, in which the collectors would correspond to a boiler that heats the water, and the closed circuit, to the return and return of a heating installation.

Heat exchanger

In the solar thermal installation, we must transfer the heat transported by means of a heat exchanger. Continuing with the simile of a heating installation, in it we give the heat to the environment through radiators, while in a solar installation, we transfer it to the water through an exchanger.

The closed circuit that joins the collectors is called Primary Circuit; The Secondary Circuit corresponds to the one that starts from the exchanger to the solar accumulation tank.

The exchangers can be external to the tank (exchangers of plates), or interiors (coil), in which case we will talk about storage cylinders.

Solar accumulation

Solar thermal energy is not consumed in its entirety instantaneously, since it depends on the existing demand at each moment, so that, in order to waste it, it is necessary to accumulate it.

Therefore, we need a system of hot water accumulation, so that it can be supplied as it is demanded.

This is achieved with the Accumulators or Interaction, which are nothing more than deposits with enough capacity and insulation to avoid, as much as possible, the energy losses.

Solar Circuit Circulation Pumps

To move the necessary flow rates, in addition to overcoming the load losses of the circuits, to circulator or pump is needed.

Conventional Auxiliary Energy Solar Energy

In periods of low thermal radiation or with high demand, we will need a support system that warms the water, independently of the solar system, called auxiliary generator.

In general, boilers are used, which will start working under these conditions, to heat the water to the pre-set temperature (setpoint temperature).

Below is a very basic scheme of a solar thermal installation, to visualize and understand these concepts forming what are called compact equipment or kit.

What are the necessary elements for security?

ad, to ensure that the installation works in optimal conditions and does not deteriorate. The following are the most important safety elements that make up a low-temperature solar thermal installation:

Expansion Glasses Solar Circuit

As the temperature of the water increases, its volume increases. Therefore, we need an element that absorbs that increase when the heat transfer fluid expands.

For this purpose, containers called  vessels or expansion tanks are used .

There are two types: open and closed. The most common are closed expansion tanks. They must be designed to work in the solar circuit.

Solar Circuit Safety Valves

It is used to control the pressure in the primary circuit. When the calibration value is reached, the valve discharges liquid to prevent the pressure of the installation reaching dangerous limits for the operation of the solar collectors and the installed devices. They must be designed to work in the solar circuit.

Glycol Solar Circuit

An ideal liquid for transporting heat in a solar thermal installation should be anti-freeze, not boil, not corrode, be toxic, have a high heat capacity and a high coefficient of heat transmission, should not be spent and should be economically accessible.

This ideal liquid “does not exist”, the closest you have reached the ideal parameters is a percentage of 60% water and 40% glycol (ethylene glycol or propylene glycol).

Heat Sink Circuit Solar Thermal Power

To avoid dangerous temperature increases in the primary circuit of the solar energy installation, it is necessary to have elements that dissipate excess heat (in the case of not using it).

For this there are different systems in the market, such as static dissipators, fan heaters, etc.

In the following infographic, different heat dissipation systems are shown. They are very interesting animations, since you can see how solar thermal installation works and how heat can be dissipated.

When the process of static dissipaters, logically, the advantages of this system are compared to the system with aerotherm (electrical) are praised.

The tab called Heat Pipe corresponds to solar collectors called vacuum tubes. You can click on each one of the tabs and numbers. It’s very interesting (only visible on a desktop computer)

Solar Thermal Power Purgers

In order to extract the air that accumulates inside the primary circuit and causes serious problems of operation of the installation, it is necessary to install purgers in the high parts. These elements must be designed to work in a solar circuit.

Automatic Control Solar Thermal Energy

For the entire system to work properly, it must have an automatic control, more or less complex, depending on the size of the installation, with probes of temperature measurement in panels, tanks, programming, activation of electric heatsink (if there is one this system), programmer, pump control, etc.

What should we take into account to obtain maximum efficiency?

Of course, the installation of solar thermal energy is a great system to take advantage of the sun’s radiation and transform it into heat.

We have a clean energy, and that will bring us great savings from the energy point of view, and consequently economic.

But for this,  the system must be efficient . Of little use, have an installation of this type, if it is poorly designed, poorly executed, malfunctioning or standing.

An installation in optimal conditions is capable of eliminating a large percentage of the conventional energy that would be used if such installation did not exist.

For our climatic conditions, the percentages saved vary between 70-80% in Sanitary Hot Water, 40% in Radiant Soil and 15% in Conventional Heating.

The solar thermal installations are amortized in a short space of time, depending on the size of the installation (between 5 and 10 years), and easily adapted to existing conventional installations.

The depreciation of the solar system is inversely proportional to the, that is, the more hot water is consumed, the more quickly the investment is amortized.

Finally, indicate that the useful life of the thermal capture systems is 20 years, so that with the amortization periods indicated above, it will be available for practically free, over a long period of time.