# Renewable Energy Systems 2023
## 2 The Research Topics Represented in This Special Issue
### Power Plants Based on Solar Systems  
[PERSON] et al. [17] developed a dynamic simulation study on the operation of a greenhouse coupled with renewable energy technologies. The paper is focused on the design of the system components in order to dynamically investigate the operation of this hybrid renewable energy plant. The plant is considered an optimal solution within the green farm framework. In particular, a 20 kW photovoltaic (PV) field is considered adequate to supply the electric energy demand of the farm, in addition to 28 m\({}^{2}\) solar thermal collectors which are designed to meet the thermal energy demand of the greenhouse when its operating temperature falls lower than a specific set point. A biomass auxiliary heater is also included. The plant is designed to produce electricity for buildings close to the greenhouse, their related irrigation pumps, and thermal energy both for the greenhouse's heating and the domestic hot water and space heating energy demands of users in the nearby buildings. As part of a bio-circular economic approach, the plant also includes a pyrogasifier fueled by wood and agricultural waste. This model is applied to a specific case study; a green farm located in Naples (southern Italy). The operation of the whole plant, the energy components, and the greenhouse are dynamically simulated in TRNSYS 18 software. The greenhouse's thermal behavior is also validated using the values in the literature. Subsequently, a detailed energy, economic, and environmental analysis of the whole plant is performed. The proposed plant is able to reduce its total equivalent CO\({}_{2}\) emissions by 148.66 t/y. In addition, it obtains good profitability, with a simple payback of only 1.7 years. [PERSON] et al. [18] presented a simplified mathematical model for the evaluation of the energy production of a PV field, as a function of its tilt angle and azimuth angle. The authors state that the developed model is useful for ordinary users of PV systems, considering the model's very small number of input parameters. The key objective of this study is the identification of the optimum locations of PV fields, considering the local weather in southern Slovakia. In their work, an experimental system based on two polycrystalline PV modules is also used. In particular, the first part of this experimental system identifies the tilt angle variation, from 0 to 90. The second module aims to calculate energy production as a function of the azimuth angle. Using the carried-out measurements, regression equations highlighting the relationships between the tilt or azimuth angle and the energy produced by the PV system are generated. Although the presented models are obtained for an area of southern Slovakia, these models, described by a simple second-degree polynomial function, can also be considered applicable to the further areas in Central Europe, if the regression equation coefficients are suitably modified. The presented mathematical model is about 4% more precise than other models used for this weather zone in southern Slovakia. Combining their analysis of the results achieved through their experimental and numerical simulation approaches, the authors found that the effect of the tilt angle and azimuth angle of a PV module on its electricity production is about 18% and 24%, respectively. This mathematical model allows for a simple forecast of PV production in real operating conditions in southern Slovakia for design, dimensioning, and optimization purposes. [PERSON] et al. [19] investigated the integration of thermoelectric generators (TEGs) into these photovoltaic and thermal collectors (PVT) in order to increase their power production. They performed an experimental and numerical comparison between a PVT panel with and without TEGs. The authors state that the novelty of the presented work is due to both the numerical and experimental analysis they performed on this kind of system. The aH60 model manufactured by Abora Solar was used to perform the analysis.