Published the 4 October 2024
Concentrated solar power concentrates the sun’s rays to generate heat and electricity. It differs from photovoltaic solar production and therefore offers a new mode of energy production. Ugo Pelay, research professor at IMT Nord Europe, explains the principles behind this system.
Ugo Pelay: As the name suggests, concentrated solar power concentrates the sun’s rays. Mirrors are used to reflect the rays toward a line or point, depending on the concentrator technology used. The irradiance is concentrated to heat a fluid called heat transfer fluid. This fluid then transmits the energy to a power cycle using an evaporator. The resulting steam then turns the turbines to generate electricity.
UP: The main advantage of concentrated solar power plants is their heat storage capacity. Photovoltaic systems require batteries to store the electricity produced, whereas concentrated solar power enables the use of thermal storage systems that are much easier to implement, have fewer environmental impacts and are less expensive. Depending on the technology used at the power plant, the heat produced ranges between 400 and 1,000°C. It can be used to generate electricity, as seen above, or used directly by industries and processes that consume thermal energy such as desalination.
UP: The difference between concentrated solar and photovoltaic power lies in their conversion methods of solar energy (in the form of electromagnetic waves). Photovoltaic panels use photovoltaic cells (electronic components) to directly convert solar energy into electrical energy based on a photoelectric effect. About 20% of solar energy is converted into electricity and 80% into heat. It is therefore a direct electronic electrical conversion process. Concentrated solar power, on the other hand, uses thermal energy from solar radiation. This is concentrated to produce high-temperature heat that is then used to turn turbines during the power cycle.
UP: Concentrated solar power mainly relies on three types of receptors or concentrators: tower, linear Fresnel, and parabolic trough.
The remote-controlled adjustable mirrors (heliostats) in the solar tower power plants reflect the sun’s rays towards a single point. The rays are concentrated in a high-efficiency cell, which is the receiver at the top of the tower. The intense concentration results in temperatures ranging between 800 and 1,000°C. The energy in the heat transfer fluid is then transferred to the power cycle (e.g. Rankine, Stirling) to produce electricity. Thermal storage systems can also be easily integrated into the plant to offset shortages or lengthen production.
Fresnel linear solar power plants use strip mirrors that can be washed automatically. They are placed in parallel rows installed close to the ground to direct the solar radiation towards stationary receiver tubes.
Parabolic trough power plants, on the other hand, have mirrors that focus the solar rays on tubes arranged at the focal axis of the concentrator. The concentrator can follow the sun’s path by rotating on an axis. Parabolic trough solar power plants can integrate thermal storage systems, just like Fresnel and tower power plants.
The concentrated solar power heat and electricity generation path. Credits: EDF.
UP: Photovoltaics offers energy efficiency of about 20%, compared to over 30% for concentrated solar power. Photovoltaic panels are the most widely used because they are easy to install, small in size and relatively inexpensive. Concentrated solar power plants, on the other hand, require huge facilities. They cover the equivalent of dozens of football fields filled with mirrors. This is not feasible for individuals but is an option for large groups and governments.
Concentrated solar power plants have a lower environmental impact than solar photovoltaics and are comparable to wind power. However, like all types of energy, they do have an impact.
UP: France currently has two concentrated solar power plants. The LLO Research and Development Plant in the Cerdagne region is the first commercial thermodynamic solar power plant with storage. The second is the Thémis demonstration solar power plant. Power plants require strong sunlight and dry air to function properly (to prevent the reflection of solar rays). This explains why there are fewer in France and more in the United States and Spain. These countries account for 80% of the world market. Electricity generation from concentrated solar power plants is currently more expensive than for wind and nuclear power. But with constantly changing electricity prices, it is highly likely that this energy will become competitive and enter the French energy mix. This technology is currently less mature than photovoltaics, yet it offers significant potential for industrial development.
UP: Many stakeholders in the concentrated solar sector, including IMT and CNRS, are conducting research in this area. Some of the work to improve the storage systems is being carried out by the PROMES laboratory. IMT Nord Europe is currently conducting research on receiver geometry to make them more efficient and to optimize the integration of multi-energy concentration plants into distribution networks.
The main challenges for concentrated solar power remain the storage of renewable energy and the optimization of components used to increase energy efficiency. The integration of concentrated solar power plants into smart grids will increase the system’s overall performance.
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