Solar Thermal Energy
Among the different applications of solar thermal energy there is the possibility of generating electrical energy. The current technology allows heating water with solar radiation to produce steam and then obtain electrical energy.
Although the principle of operation is very similar there are two main applications of solar thermal energy:
- Use of solar thermal energy in homes and small installations
- Large thermal solar power plants. In these plants the heat is concentrated in a point to generate steam, with the steam a turbine is driven to generate electric power. Once the heat is generated, the operation of a solar thermal power plant is very similar to that of a thermal power plant or a nuclear power plant. The difference lies in the fact that a thermal power plant the heat to generate the steam comes from the combustion of fossil fuels, normally coal, and in a nuclear power plant, heat is obtained by fissuring the nucleus of uranium atoms.
The collectors of solar thermal energy are responsible for capturing the thermal energy of solar radiation. These solar collectors are classified as low, medium and high temperature collectors depending on the way they work.
- Low temperature collectors . They provide useful heat at temperatures below 65 ° C.
- Medium temperature collectors . They are the devices that concentrate solar radiation to deliver useful heat at a higher temperature, usually between 100 and 300 ° C.
- High temperature collectors . They work at temperatures above 500ºC. They are used for the generation of electrical energy.
Systems that form a solar thermal installation
The basic scheme of a solar thermal installation is the following:
A solar thermal installation consists of several systems:
Solar radiation collection system
The solar radiation collection system consists of solar collectors connected to each other. Its mission is to capture solar energy to transform it into thermal energy, increasing the temperature of fluid circulating through the installation.
Among the different solar collection systems we highlight:
- Flat solar collector. It is the most widespread solar collector, you can get temperature increases of 60 ° C at a reduced cost. It is used in low temperature thermal solar plants.
- Solar thermal collectors not glazed. It is common, for example, to heat the water in swimming pools. The temperature increase is low, around 30 ° C. They are more economical than flat solar collectors.
- Vacuum solar collectors. They consist of metal tubes that cover the metallic tube that contains the working fluid, leaving between them a chamber that acts as an insulator. They have a very high yield, but their cost is also high.
- Solar collectors with radiation concentration systems. They are used for installations that require higher temperatures. Parabolic or semi-cylindrical panels are used.
- Solar thermal collectors with tracking systems of the position of the Sun. Its position varies throughout the day to maintain a position perpendicular to the received solar radiation.
Thermal solar energy accumulation system
It consists in storing the heat energy in an accumulation tank for its later use. The hot water obtained through the collection system is conducted to the place where it will be used.
The stored hot water can be used directly, as is the case of heating the water of a pool, in hot water or heating applications the demand.
Because the moment of need for hot water does not always coincide with the moment when there is enough radiation it will be necessary to make the most of the hours of Sun to accumulate the thermal energy in the form of hot water.
The thermal energy storage system consists of one or more hot water tanks. The size of the storage tanks must be proportional to the estimated consumption and must cover the hot water demand of one or two days.
Distribution system of solar thermal energy
Once the solar collectors have heated the heat carrier medium (water or air) increasing its thermal energy, we can transfer this thermal energy to other colder sources.
In this system all the elements destined to the distribution of the medium carrying heat and conditioning to consumption are included: control, pipes and conduits, expansion vessels, pumps, purgers, valves, etc. Also part of this system is the support system based on conventional energies (electric, gas boiler or gas oil), necessary to prevent possible faults derived from the absence of solar radiation and deal with peak demand.
Conventional energy support systems
The solar thermal installations need conventional support systems in anticipation of the lack of solar radiation or consumption exceeding the dimensioning. In most cases, both in installations in single-family homes and in residential buildings, solar installations are designed to provide homes with 60-80% of the hot water demanded, although in areas with high sunshine throughout the year. year, the contribution percentage is usually higher.
These energy support systems can be from various sources. If the installation is connected to the network, it can take advantage of the electricity supply of the electric company itself. In other cases you can use other sources of renewable energy (wind energy or hydroelectric power if conditions permit) or non-renewable energy sources. Non-renewable energy sources can be from fossil fuel derivatives ( oil, coal or natural gas), in some installations pellet or biomass boilers are used.
In the months of lowest solar radiation, it does not reach 60% of the energy needs. On the contrary, in the summer months almost 100% of them are reached. Thus, the objective with which solar thermal installations are designed is to cover a minimum of 60% of the annual energy needs depending on the geographical area.
Trying to cover over 60% or 70% per year of solar thermal energy would require placing a very large solar field, which would result in an extremely high cost that would never be amortized. In addition, such a large solar thermal installation would cause in the months of increased solar radiation a production surplus that could not be used and would cause overheating problems throughout the installation.
For this reason the facilities that work best and are profitable before are those that need sanitary hot water for the whole year, heating for winter and have a pool for summer or even all year.
Economic and social aspects of a solar thermal installation in a house
The initial investment of a solar thermal system will be greater compared to a conventional energy supply system. On the other hand, the operating cost during the more than 25 years of life of the solar thermal installation will be irrelevant compared to the purchase of fuel or electric power, repairs, maintenance, etc. associated with the conventional energy system.
The installation of solar thermal energy is economically more economically advantageous, since all the energy that we obtain from the Sun with the solar thermal sensors, will be energy that we will save it from producing (burning fuel in a boiler) or consuming (from the electric network of distribution). A solar thermal installation ends up being profitable throughout the years, since the energy saving that it produces materializes in economic savings, which allows to end up amortizing the cost of the installation. This amortization can vary between 5 and 12 years depending on the size of the installation, the aids obtained in the form of a lost fund, the place where it is installed (more or less solar radiation) and the greater or lesser needs of the user.
In the case of placing these solar thermal installations in new construction or rehabilitation houses, the amortization can be considered instantaneous, since the increase that represents in the total price of the house is very small; the amount paid for that higher cost in a mortgage loan each year is less than the amount in euros that involves the lower cost of gas or diesel.
We highlight the main advantages of a solar thermal system:
- Economic advantages For the same needs, the conventional system will need to consume less fuel (derived from fossil fuels or biomass), which will represent a lower annual expense for the user. In addition, solar energy is independent of conventional fuel and its supply, since it is compatible with any conventional system and independent of the variation in the purchase price of fuel.
- Environmental advantages, since the generation of energy with conventional systems has very significant environmental costs (CO2 emissions , climate change, greenhouse effect, discharges, nuclear waste, acid rain, etc.) in relation to solar systems. On average, one m2 of solar thermal collector is able to prevent the emission into the atmosphere of one ton of CO2 each year .
- Easy maintenance. The useful life of thermal solar installations is greater than 25 years and the maintenance required, although it is necessary to do, is much less important than in the case of conventional systems.
However, the installation of thermal systems presents a drawback: it requires the installation of the same conventional system that would result if the solar collectors were not installed. Sometimes it is problematic to assemble them in existing buildings as a consequence of their lack of foresight at the project level.
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Last review: April 17, 2018