Solar Thermal Energy
Solar thermal energy consists of harnessing energy from the Sun to transfer it to a medium that carries heat, usually water or air. It is a form of renewable, sustainable and environmentally friendly energy. This way of generating energy can be applied in homes and small installations but also in large solar thermal power plants.
Among the different applications of this renewable energy source there is the possibility of generating electricity through a solar thermal power plant. Current technology allows water to be heated with solar radiation to produce steam and subsequently obtain electrical energy. Although the thermodynamic performance is not very high compared to other systems, the price of fuel is zero.
Principle of operation of a solar thermal power plant
The principle of operation of this type of solar radiation is very similar, there are two main applications of solar thermal energy. In these solar thermal power plants, solar radiation is concentrated at a point to generate steam, with steam a steam turbine connected to an electric generator is activated. The electric generator is responsible for transforming mechanical energy into electricity. 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 way of generating heat to obtain steam. In a thermal power plant the heat comes from the combustion of fossil fuels (usually coal), in a nuclear center the heat is obtained by fissuring the nucleus of uranium atoms and, finally,
Solar thermal energy collectors 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 degrees Celsius.
- 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 electric power generation.
The basic scheme of a solar thermal energy installation is as follows:
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. The function of these panels is to capture solar energy to transform it into thermal energy, increasing the temperature of the fluid that circulates through the installation.
There is a large number of solar radiation collection systems. The choice of one system or another will depend mainly on whether it is solar thermal installations of low, medium or high temperature.
Among the different solar collection systems we highlight:
- The flat solar collector. It is the most widespread solar collector, temperature increases of 60 degrees Celsius can be obtained 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 pool water. The temperature rise is low, around 30 degrees Celsius. They are cheaper than flat solar collectors.
- Solar vacuum collectors. They consist of metal tubes that cover the metal 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. Panels in parabolic or semi-cylindrical shapes are used.
- Solar thermal collectors with tracking systems for the position of the Sun. Their position and inclination varies throughout the day to maintain a position perpendicular to the solar radiation received.
Solar thermal energy accumulation system
A solar thermal energy accumulation system consists of storing the heat energy in an accumulation tank for later use. The hot water obtained through the collection system is taken to the place where it will be used.
Stored hot water can be used directly, as is the case of heating a pool's water, in domestic hot water applications or heating 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 thermal energy in the form of hot water.
The thermal energy accumulation system consists of one or more hot water tanks. The size of the storage tanks must be proportional to the estimated consumption and must meet the demand for hot water for one or two days.
Solar thermal energy distribution system
Once the solar collectors have heated the heat-carrying medium (water or air) by increasing its thermal energy, we can transfer this thermal energy to other cooler sources.
This system includes all the elements destined to the distribution of the heat-carrying medium and conditioning for consumption: control, pipes and pipes, expansion vessels, pumps, traps, valves, etc. Also part of this system is the support system based on conventional energy (electric, gas boiler or diesel), necessary to prevent possible failures arising from the absence of solar radiation and cope with demand peaks.
Conventional energy support systems
Solar thermal energy installations need conventional support systems in anticipation of the lack of solar radiation or a consumption greater than the size. In most cases both in installations in single-family homes, as in residential buildings, solar installations are designed to provide homes with 60-80% of the hot water demanded, although in areas with great sunshine throughout the year, the contribution percentage is usually higher.
These energy support systems can be from various sources. If the installation is connected to the network, the electricity supply of the electricity company itself can be used. In other cases, other renewable energy sources (wind energy or hydraulic energy may be used if conditions permit) or non-renewable energy sources. Non- renewable energy sources can be derived from fossil fuel derivatives (oil, coal or natural gas), in some facilities pellet or biomass boilers are used.
In the months of lowest solar radiation, 60% of energy needs are not met. On the contrary, in the summer months practically 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.
Pretending 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 a surplus of production in the months of greatest solar radiation that could not be used and that 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 swimming pool for summer or even the whole year.
Economic and social aspects of a solar thermal energy installation in a home
The initial investment of a solar thermal energy system will be greater compared to a conventional energy supply system. On the other hand, its 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 electrical energy, repairs, maintenance, etc. associated with the conventional energy system.
One of the advantages of solar energy is in the economic part: all the energy we obtain from the Sun with solar thermal collectors, will be energy that we will need to produce (burning fuel in a boiler) or to consume (from the electricity grid of distribution). A solar thermal energy installation ends up profiting over the years, since the energy savings it produces are realized in economic savings. Over the years, economic savings will allow us to amortize the cost of the installation. This amortization can range between 5 and 12 years depending on the size of the installation, the aid obtained thoroughly lost, the place where it is installed (more or less solar radiation) and the needs of the user.
In the case of placing these solar thermal installations in newly built or rehabilitated homes, depreciation can be considered instantaneous. The increase that represents in the total price of the house is very small; The amount that is paid for that higher cost in a mortgage loan each year is less than the amount in euros that is the lowest cost of gas or diesel.
We highlight the main advantages of solar thermal energy:
- 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 power generation systems has conventional very important environmental costs (CO 2 , climate change, greenhouse, waste, nuclear waste, acid rain, etc.) in relation to solar systems. On average, a m 2 of solar thermal collector is able to avoid the emission of one ton of CO 2 into the atmosphere every year .
- Easy maintenance. The useful life of the solar thermal installations is over 25 years and the maintenance that it requires, although it is necessary to do, is much less important than in the case of conventional systems.
However, one of the drawbacks of solar thermal energy is that the installation of the same conventional system as the one that would result if solar collectors were not installed is required. Sometimes its assembly in existing buildings is problematic as a result of its lack of forecast at the project level.
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Last review: September 12, 2019