This electricity generation process is carried out in so-called thermoelectric solar power plants or solar thermal power plants. The first solar thermal power plants were built in Europe and Japan in the early 1980s.
What Is the Difference Between Thermoelectric Power and Photovoltaics?
The difference between thermoelectric power is the way of producing electricity.
Thermoelectric power plants work by concentrating solar radiation in a focus point to generate steam. Afterward, the steam drives turbines and generates electricity.
On the other hand, photovoltaic solar panels use another physical principle: the photoelectric effect. Solar panels are made of a material that, when whet a photon hits it, the material releases an electron, generating an electric current.
What Is Thermoelectric Energy?
Thermoelectric power generation uses this effect to generate electricity. So, for example, thermoelectric generators could convert residual heat into additional electrical power.
Thermoelectric energy is called three phenomena related to each other by Thomson's relations, discovered by Lord Kelvin :
1. Seebeck Effect
The Seebeck effect occurs when two dissimilar metals at different temperatures are brought into contact to form a bimetallic bond. An electromotive force is generated between the two sides of the bond.
This phenomenon is the basis for the operation of thermocouples, a thermometer used to control gas flow in household devices such as ranges, space heaters, and tap water heaters.
2. Peltier Effect
The Peltier effect occurs when a current is made to circulate through a bimetallic joint. To keep the temperature of the joint constant, heat must be supplied or extracted, depending on the direction of circulation.
This phenomenon has a practical application in small refrigeration devices, having the advantage, unlike refrigerators based on the compression and decompression of gases, of not having moving parts that wear out.
3. Thomson Effect
Less well-known is the phenomenon called the Thomson effect, discovered by William Thomson, Lord Kelvin.
It occurs when a current flows through a homogeneous conductor of constant cross-section where a temperature gradient has been established. In order to keep the temperature distribution invariant, heat must be supplied or extracted from the conductor.
What Is the Thermoelectric Effect?
The thermoelectric effect is the conversion of temperature difference to electrical voltage and vice versa. A thermoelectric device creates a voltage when there is a difference in temperature on either side. On the contrary, when a voltage is applied, it makes a temperature difference.
At the atomic scale (especially charge carriers), an applied temperature gradient causes charged carriers in the thermoelectric material, whether electrons or holes, to diffuse from the hot side to the cold side. It occurs similarly to a classical gas that expands when it is heated. Therefore, the current is thermally induced.
This effect can be used to produce electricity, measure temperature, cool objects, or heat or cook them. Because the direction of heating or cooling is determined by the sign of the applied voltage, thermoelectric devices produce very convenient temperature controllers.
How Does a Thermoelectric Power Plant Work?
The operation of a thermosolar power plant is similar to that of a thermal or nuclear power plant. The distinctive element between them is the fuel or the heat source.
Thermal power plants use fossil fuels such as coal or gas to generate heat. Nuclear power plants use the nuclear energy in uranium atoms to produce thermal energy. On the other hand, thermoelectric plants use solar radiation.
Mirrors concentrate the sun's rays in a receiver that reaches high temperatures of up to 1,000 degrees Celsius. This heat energy is used to heat a fluid and generate steam. The steam generated increased pressure, allowing a steam turbine to move. At the same time, this turbine drives a generator that will be in charge of converting mechanical energy into electricity.
What Techniques Are Used to Concentrate Solar Radiation?
Different types of concentrators with different maximum temperatures are obtained with their corresponding thermodynamic efficiencies. They are as follows:
Parabolic troughs solar collectors: A parabolic cylindrical solar concentrator consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line.
Compact linear Fresnel reflectors: they are made of reflectors are made of many thin, flat strips of mirrors that focus sunlight onto tubes into which the working liquid is pumped.
Stirling Disc is a reflector that follows the Sun in two axes. In particular, the disc is a unique parabolic reflector that concentrates light into a receiver positioned at the reflector's focal point.
Central solar power tower: these kinds of solar power plants consist of a set of reflectors called heliostats that concentrate sunlight onto a central receiver installed in a tower. Because the relative position of the Sun varies, heliostats must have the ability to reorient themselves by tracking on two axes.
What Are the Pros and Cons of This Technology?
Like all technologies, solar thermal power plants have pros and cons:
Advantages of Solar Thermal Power Plants
The main advantage is that the fuel used is solar radiation.
It is a free and inexhaustible resource. For this reason, we can treat it as renewable energy.
Its energy conversion efficiency is higher than regular PV power systems.
Disadvantages of Solar Thermoelectric Energy
The main drawback is in the schedule and weather that does not allow a constant amount of electrical energy to be generated.
Initially, the first plants could only operate during the hours of solar irradiation, but today it is possible to store heat during the day to produce electricity at night.
On the other hand, the maintenance of these facilities involves constantly cleaning large surfaces of reflectors. For this reason, the consumption of water and chemical products is abundant.
What Is the Influence of Geography on Solar Thermoelectric Plants?
Concentrated thermal energy systems always consist of mirrors and lenses that group direct sunlight and a receiver that contains a liquid heated by the grouped light.
The diffuse part of sunlight, the amount of light scattered by clouds and particles in the atmosphere, cannot be grouped and is therefore not used by this system. As a result, solar thermal systems are only suitable for areas with little cloud.
For example, in the Netherlands, 60% of the light consists of diffused light. Therefore, solar thermal energy cannot be used in the Netherlands and Flanders, but there is sufficient solar energy in the tropics and southern Spain, Italy, and Greece.
Why Are Solar Farms Not Created in Deserts?
Theoretically, mirror power plants in the Sahara in an area the size of France (1/5 of the Sahara) can provide current global energy consumption. However, in Europe, two practical obstacles hold investors back:
Cooperation between European and North African countries is such that investment risks are more significant in North Africa than within the EU.
The organization of electricity transmission between the continents, although there are already power lines.