The future of thermodynamic solar energy in Italy starts from Sicily, where it was “ideally” born with the burning mirrors of Archimedes from Syracuse. Thanks to the alliance between ENEA and the Italian industry, in fact, the first plant built in Italy that integrates concentrated solar power with photovoltaics will soon be inaugurated in Partanna (Trapani) and another to be built in Trapani nella Piana is already in the pipeline. by Misiliscemi. In the two projects ENEA has the role of technical supervisor, the Italian companies SOL.IN.PAR. srl and Stromboli Solar srl are the clients and FATA spa of the Danieli group builds the plants.

“These two projects demonstrate that in Italy there is an industrial reality that is investing in thermodynamic solar technology with concrete initiatives despite bureaucratic and regulatory constraints”, underlines Giorgio Graditi, director of the Energy Technologies and Renewable Sources Department of ENEA. "ENEA has been involved in these two plants to carry out various activities, from the supervision of the design, construction and start-up, to the verification of performance, up to the integration of the concentrated solar plant with photovoltaic technology", continues Graditi.

The Partanna plant has an installed capacity of 4.26 MWe and is capable of producing electricity for over 1,400 families (about 30% of the population of the municipal area, with 3 kW domestic users). "We expect to reach a thermal energy storage capacity of 180MWht, which is equivalent to about 15 hours of operation of the system at full load, even in the absence of solar radiation," explains Graditi.

The integration of thermal energy storage systems is an important aspect, since it allows you to have thermal energy that can be converted into electricity and, therefore, to program production to meet the energy demand. In this way, it is possible to decouple the collection of solar energy - which depends on the day-night cycle and the weather conditions - from the production of electricity, linked instead to the demand from users. In Partanna the total area of the solar field is 83,000 m2 (about 10 football fields), where 126 linear Fresnel-type solar collectors are installed, arranged in 9 loops [1], capable of focusing the sun's rays on a tube receiver; a low-cost, non-flammable, harmless to the environment mixture of molten salts (mainly potassium and sodium nitrates) flows inside (in case of circuit leaks, easy to remove because they solidify quickly), which is used both as a heat transfer fluid, and as a means of accumulating thermal energy at a stable temperature of about 550 ° C. The fluid heated in the solar receiver accumulates in the hot tank [2], then enters the steam generator where it releases its energy and is discharges into the cold tank and returns to the solar receiver from there. The steam produced is sent to a generation group, a steam turbine / alternator, with a power of 4.26 MWe. The plant is completed by a first start-up boiler fueled with LNG - about 47 t stored in a cryogenic tank - to ensure that the temperature of the molten salts is maintained above the freezing point, especially in winter and during the filling phase. initial of the tanks.

In addition to the two plants in Sicily, in Italy there are other initiatives in the field of thermodynamic solar: starting from 2019, this technology is among the strategic themes of the Research of the Electric System, the three-year research program on new energy technologies funded by the Ministry of Economical progress. In this context, ENEA presented a three-year research plan on the main components of concentrating solar plants, which envisages the study of new heat transfer fluids, the development of innovative surface coating materials for receiver tubes and the construction of advanced thermal storage systems. Furthermore, by 2021 an experimental platform for the characterization of components for the supply of industrial heat at medium and high temperatures will be created at the ENEA Casaccia Research Center (Rome). "The process heat market can prove to be an effective tool for promoting thermodynamic solar energy: in this sector the competition with other renewable energy technologies is less strong and the applications that would allow to trigger the virtuous circuit of the economy of scale are significantly expanded. , even in the short-medium term ”, underlines Giorgio Graditi. The medium / high temperature heat produced by a concentrating solar plant could be used to power, for example, some processes in the pharmaceutical, food and textile industries, but also to produce 'green' fuels and hydrogen from biomass and water (electrolysis ). "The energy consumption of the industry represents about 32% of all energy globally required and, of this share, only 26% is attributable to electricity consumption, while the remaining 74% is attributable to thermal energy consumption, which could to be satisfied by concentrating solar plants integrated into the industrial process ”, concludes Graditi.

In the next decades, the International Energy Agency expects a substantial increase in the share of energy produced by thermodynamic solar, which should cover more than 10% of the global primary energy needs by 2050. Aim to improve the thermal energy storage capacity of the systems it will be essential to attract further investment.

While in Italy large-scale plants (over 20-50 MW) are difficult to build due to specific geographical conditions and authorization restrictions, the countries where this technology has found greater application development worldwide are Spain and United States, which leads the ranking with the highest installed and operating power, with 2.3 GW and 1.8 GW respectively; followed by China, Morocco and South Africa. A further boost to the development of this technology also comes from the United Arab Emirates and India, countries at the forefront with new plants under construction of 700 MW and 290 MW.

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