## 2 Construction Aspects for Energy Performance Improvement
### Location and Orientation
#### 2.1.2 Influence of Solar Radiation on Greenhouses  
Solar radiation, the primary source of energy for greenhouses, is essential in the cultivation of plants and the energy efficiency of agricultural operations. The design of modern greenhouses seeks to maximize sunlight absorption by adjusting specifically to the demands of the plants and the climatic conditions of the site. The intensity and quality of sunlight are modulated as needed through shading systems and the choice of appropriate roofing materials because they are critical to maintaining an optimal growing environment, as discussed by [46; 47]. Such decisions are guided by factors such as latitude, altitude, seasonality, and meteorology, with the aim of maintaining an optimal environment for vegetative development [48; 49]. [PERSON] et al. [50] proposes an improved model to calculate the total solar radiation transmitted by transparent curved surfaces in greenhouses. This model emphasizes the importance of external soil reflection, a component often overlooked in previous studies, highlighting how solar radiation reflected by the soil contributes significantly to the total radiation received inside the greenhouse. By incorporating external soil reflection, the model offers a more accurate and comprehensive approach to the efficient design of solar greenhouses, allowing for the optimization of the greenhouse's aspect ratio for different latitudes in order to maximize solar radiation capture and improve the plant growth environment. The insertion of photovoltaic technology in greenhouses provides dual functionality: Converting solar energy into electricity to power indoor operations, decreasing reliance on external energy sources, and providing power for irrigation systems and other agricultural equipment [44; 51; 52]. This approach not only lowers operating costs but also reinforces the facility's energy self-sufficiency. The integration of photovoltaic systems in greenhouses, such as organic semi-transparent solar cells (OSCs), can create an annual energy surplus in hot and moderate climates while minimizing the reduction of sunlight entering the greenhouse with an appropriate design [44]. [PERSON] et al. [53], developed mathematical models to optimize the distribution of sunlight within Chinese solar greenhouses, highlighting the importance of understanding the impact of solar radiation on the greenhouse environment. These models are critical not only to assess the quality of the light environment, but also to enable the optimization of greenhouse design, lighting regulation, and planting pattern, with a view to maximizing energy efficiency and improving crop growing conditions. By quantifying the allocation of solar radiation and obtaining the dynamic spatial distribution of solar radiation, the study provides valuable information to enhance the low-light environment near the north wall and optimize the storage capacity and heat release of the north wall, which are critical aspects for the success of solar greenhouse farming. The integration of photovoltaic (PV) systems in greenhouses faces several limitations, including high implementation and maintenance costs that may hinder their large-scale adoption [54]. Technical challenges such as the limited efficiency of solar cells due to losses from radioactive and non-radioactive recombination, parasite resistance, and poor light management are also significant barriers [55]. Shading caused by nearby structures or by the greenhouse structure itself can reduce the power generated by the PV system, severely affecting its performance [56]. In addition, the connection of photovoltaic plants to the electrical system requires careful analysis to ensure voltage stability, which poses another technical challenge [57]. These limitations highlight the need for ongoing research and development to overcome the technical and economic hurdles associated with implementing greenhouse PV systems.