Concentrated solar power is a long-standing yet innovative technology that we have improved to make it even more efficient. It works based on a simple principle whereby a parabolic mirror concentrates the sun's rays into a single point called the “fire” point, generating a temperature of around 550°C. A pipe is run through at this point, through which a fluid with the ability to store heat flows before passing through an exchanger so that it can be used to generate industrial steam or run a turbine and produce electricity. The use of a heat transfer fluid with optimised composition allows the plant to remain in operation even at night, reusing the heat it has absorbed during the day. This type of plant has been used since the 1970s and the principle of the parabolic mirror has been known since ancient times, with Archimedes said to have made a weapon out of it to set enemy ships on fire. Our Renewable Energy and Environmental R&D Centre in Novara, in collaboration with the Politecnico di Milano and the MIT in Boston, has taken this technology to the next level in terms of efficiency, making it easier to produce, use and install.
Of all of the sources of renewable energy, solar is one of the most widely used, in both its photovoltaic and thermal forms. The limitation of this type of energy source, however, is its intermittency and variability; after all, the sun, by definition, only shines during the day and with varying levels of intensity depending on weather conditions. Concentrated solar power also has these limitations because the fluid inside it, which is normally a molten salt, needs high temperatures of approx. 270 °C to be able to flow through the circuit. Below this it gets too viscous to be able to be pumped through the pipes. If the temperature drops below 250°C, the salts solidify and turn into ceramic blocks and the plant has to be discarded. For this reason, concentrated solar systems not only fail to produce energy at night or in bad weather but in fact consume it because it is needed to keep the heat transfer fluids warm. Our aim was to broaden the range of applications and the periods for which such systems could be used in order to make them profitable and to be able to integrate them into our industrial operations, for example, and we have succeeded in this by introducing some major engineering improvements.
We had to make concentrated solar power more efficient, economical and versatile in order to make it more appealing from an industrial perspective and we went about this by targeting four aspects of the plant, these being the mirror, the coating on the circuit tube, the heat transfer fluid and the overall design. We chose a special PET and silver film for the reflective surface that is much more economical than a traditional glass mirror. The circuit tube through which the fluid flows, on the other hand, is made of steel and ceramic plywood with optimised thermal properties including 95% absorbance and 7% emissivity at 550°C. With regards to the heat transfer fluid, meanwhile, we went for a mixture of molten salts that solidifies at around 100-150°C - a temperature threshold that is much lower than the temperature at which the fluids currently used solidify, namely around 250°C. Finally, in terms of the overall design, we adopted the simplest possible solutions to enable us to commission the construction and assembly of the corresponding systems from local workers in the countries in which we operate, even those located great distances from the large production complexes. These improvements have collectively halved the cost of the entire plant and reduced the cost of the mirrors four-fold.
The Concentrated Solar Power technology - Eni Video Channel
Our CSP systems are more economical, efficient and versatile than standard systems, meaning that they are suitable for a wide variety of applications. They can notably be incorporated into upstream, downstream and chemical production sites to provide industrial steam for production cycles or to run thermoelectric power plants with a lower environmental footprint. We are currently developing the first experimental plant in Gela. The heat emitted by the heat transfer fluid can be used in the upstream sector in particular to improve hydrocarbon recovery. The system can also be very useful in other fields, such as heating and supplying electricity to civic buildings, with or without thermal storage
Technologies that exploit renewable sources, including concentrated solar power (CSP), luminescent solar concentrators (LSC) and the organic photovoltaic (OPV) technology, are an integral part of the decarbonization process. The advantage of our CSP technology is its cost-effectiveness, simplicity and versatility, all of which mean that it can be easily and broadly applied even in areas a long way from logistics infrastructures, as is the case in many of the scenarios in which we operate. In such contexts, concentrated solar power could contribute positively to community life, whether by producing low-carbon thermal or electrical energy or by supporting the local economy and employment, since it could be developed directly at the site.
Data, performance and results
Temperature reached by the heat transfer fluid
Solidification point of the fluid
Absorbance of the tube through which the fluid flows
Emissivity of the tube (at 550°C)
Read more on renewables
Selected contents on this issue.