Giuseppe Langella

Agrivoltaic systems represent an innovative solution for integrating renewable energy production with agricultural activity, optimising land use and improving overall energy efficiency. This technology involves the installation of photovoltaic panels above crops, with variable configurations in terms of height, inclination and coverage density, in order to maximise electricity generation without compromising agricultural yields. The energy performance of an agri-voltaic system depends on multiple factors, including the available solar irradiation, the efficiency of the photovoltaic modules, the shading induced on crops and local climatic conditions. Compared to traditional photovoltaic systems, agri-voltaic systems can be penalised in terms of performance, as they also have to meet the agronomic needs of the crops with which they are integrated; energy density and installed power per unit area are also penalised. The paper analyses the energy performance of the main types of agri-voltaic applications, also highlighting the environmental benefits they present, providing a concrete opportunity to combine environmental sustainability and energy efficiency. Finally, it analyses the future prospects of these systems, which research and technological innovation are fostering, thanks also to the use of management systems based on artificial intelligence.

This article examines the prospects of Scheffler solar receivers integrated into renewable energy power plants for civil applications. This kind of solar receiver can offer satisfactory energetic performance with acceptable energy conversion efficiency when compared to other technologies to harness solar energy since the high-quality focal receiver can reduce heat losses also supposing great levels of evaporation temperature. In this research, energetic optimization and a broad assessment of Scheffler-type solar receivers are thoroughly conducted for variable sun radiation and considering a broad range of working conditions. To achieve this goal, thermodynamic optimization of the chief factors was attained via a numerical model which calculated the energy efficiency of the Scheffler solar receiver at part-load working conditions by computing all energy losses negatively affecting the heat exchange phase in the cavity receiver. The results obtained in this study show that the solar collector efficiencies of Scheffler receivers appear more promising than that of usual parabolic trough collectors; moreover, Scheffler receivers persisted with less sensitivity to reductions in solar radiation intensity. For these reasons, solar power systems based on Scheffler-type systems can be used from tens to hundreds of kW to ensure the energetic supply of small urban settlements with acceptable efficiency, optimistic investments, simple construction and reduced overall sizes.

The paper addresses the prospects and challenges associated with the use of ammonia in gas turbine plants. The complexity of the chemical kinetic mechanisms of ammonia combustion and the insufficient amount of experimental data that can confirm the results still require a lot of scientific research. In this sense, this application is even less technologically mature than other sectors such as the marine engine one. From the point of view of combustion in gas turbines, the techniques in use and being perfected to deal with flame instability, low laminar burning velocity (about 20% of that of methane-air flames), the long ignition delay time and low volumetric heat release rate. In particular, the use of ammonia blended with other combustion enhancers such as hydrogen, methane and alcohols has been analyzed. Mild combustion is also being analyzed as a valid technique for dealing with the difficulties of ammonia combustion. The combustion of ammonia generates significant quantities of nitrogen oxides, both for the thermal mechanism and for the “fuel” one, which must therefore be mitigated, together with the emission of unburnt ammonia. Even in this case, blending with other fuels allows for improved emissions performance. The paper compares the different techniques and the relative advantages both in terms of combustion efficiency and emissions. Finally, the perspectives for the use of ammonia in gas turbines are outlined, highlighting the challenges still to be overcome, in a panorama of energy transition towards an increasingly decarbonized future, with the aim of mitigating climate change as much as possible.