Fresnel solar thermalA Fresnel type installation is one of the variants that exist within the solar thermal power plants. Let's see what they are and how this type of solar reflectors work.
A solar thermal fresnel is an installation that collects the sun's rays in a long tubular receiver to generate heat and electricity. This type of power plant obtains the concentration of solar radiation through a cylindrical or trapezoidal surface with the capacity to absorb heat from several meters away. They are known for their practicality, simplicity and low cost.
How does a Fresnel installation work?First, a set of mirrors focus the incident light on the receiver. These reflecting devices are a set of solar concentrators that are mounted on tubes and move according to the position of the sun. The concentrators have a reflection property suitable for concentrating the sun's rays as parallel as possible to a receiver.
The receiver is a trapezoidal-shaped compartment covered with silver-plated glass. This reduces losses due to convection and radiation itself. Inside it there is a set of tubes through which a fluid circulates. This fluid is driven by a pump which circulates it to a heat exchanger. In the following process, the fluid is heated by sunlight and this is used to generate water vapor. The steam generated will be used to produce electricity through a turbine.
Solar tracking mechanism.
This mechanism of the fresnel installation ensures that the set of concentrators moves according to the position of the sun throughout the day to maintain a position as perpendicular as possible. The most typical orientation is North-South because it maximizes the annual production.
Thermal storage of this installation
This type of installation usually consists of a thermal storage. This is done so that during the night hours or when the radiation is low (e.g. due to clouds) electricity is generated from the stored heat.
What is the world's largest Fresnel plant?
The Fresnel solar thermal power plant, which is considered the largest in the world, is located in the Murcian municipality of Calasparra. This plant has the capacity to generate 50 million KWh per year, producing electricity for around 12,000 beneficiaries and reducing annual CO2 emissions by 16,000 tons.
Comparison between fresnel and parabolic trough concentrators
The curved shape of parabolic trough mirrors allows their efficiency to reach up to 15% higher than that of fresnel mirrors, resulting in significant cost and material savings. Due to the simplicity of their development and function, they have a greater reduction in efficiency.
Fresnel concentrators tend to use a longer focal length, so they are able to replace large parabolic concentrators with flat mirror segments that capture the sun's rays on elevated and fixed linear receivers. This makes the structure lighter and the mirrors, the foundations and the connections to the hydraulic circuit in general simpler and more economical.
Taking into account that solar thermal fresnel systems do not require large extensions between collectors, they will occupy less space and will be relative to their performance. The space underneath the collectors can be used to advantage for solar heat production and for incorporation into industrial and large-scale processes.