These types of plants have the same operating principle as thermal plants or nuclear plants. The difference is the heat source. In solar thermal power the source of heat is the Sun while in the others it is fossil fuels and uranium respectively.
How does a solar thermal power plant work?
The operation of a solar thermal power plant is based on obtaining heat from solar radiation and transferring it to a heat-carrying medium. Generally it is water.
In order to raise the water temperature to the desired high levels, the maximum solar radiation must be concentrated at one point. In this way temperatures of 300ºC to 1000ºC can be obtained. The higher the temperature, the greater the thermodynamic performance of the solar thermal power plant.
The capture and concentration of the solar rays are made by means of mirrors with automatic orientation that point to a central tower where the fluid is heated, or with smaller mechanisms of parabolic geometry. The whole of the reflective surface and its orientation device is called a heliostat.
There are various thermodynamic flows and cycles used in experimental setups. The cycles used range from the Rankine cycle, (used in nuclear power plants, coal-fired power plants) to the Brayton cycle (natural gas power plants). Many other varieties such as the Stirling engine have also been made. The most used cycles are those that combine solar thermal energy with natural gas.
What is the efficiency of a thermoelectric power station?
The efficiency of a solar energy concentration system will depend on the following factors:
- The technology used to convert solar energy into electrical energy.
- Receiver operating temperature and heat rejection.
- Thermal losses in the system
- The presence or absence of other system losses
In addition to conversion efficiency, the optical system that concentrates sunlight will also add additional losses.
Real-world systems claim a maximum conversion efficiency of 23-35% for "power tower" type systems, operating at temperatures of 250-565 degrees Celsius. With a combined cycle turbine the efficiency is higher.
Dish Stirling systems, operating at temperatures of 550-750 degrees Celsius (277 to 477 degrees kelvin), claim an efficiency of approximately 30%.
Due to the variation in the incidence of the sun during the day, the average conversion efficiency achieved is not equal to these maximum efficiencies. The annual net efficiencies from solar to electricity are 7-20% for power tower pilot systems, and 12-25% for demo scale Stirling plate systems.
What environmental effects do solar thermal power plants cause?
Thermal solar power plants have a series of environmental effects, particularly in:
- The high use of water.
- Large occupied surfaces.
- The use of hazardous materials.
- Effects on birds.
Water is generally used to cool and clean mirrors. Cleaning agents (hydrochloric acid, sulfuric acid, nitric acid, hydrogen fluoride, acetone and others) are also used for cleaning semiconductor surfaces.
Some projects are looking at various approaches to reduce the use of water and cleaning agents, including the use of barriers, non-stick coatings on mirrors, water mist systems, and others.
Effects on wildlife and birds
Insects can be attracted to bright light caused by concentrated solar technology, and as a result, birds that hunt them can be burned if they fly close to where the light is focused.
This can also affect birds of prey that hunt birds.