## 2 Construction Aspects for Energy Performance Improvement
### Greenhouse Construction
#### 2.2.2. Covering and Insulation Material for Greenhouses  
Greenhouse covers refer to the materials used to cover and protect the structure of the greenhouse [89]. Proper selection of roofing materials and insulation strategies is crucial for optimizing the indoor microclimate, maximizing energy efficiency, and promoting optimal plant growth. The choice of greenhouse cover also significantly impacts the quality and quantity of light entering the greenhouse, which is essential for photosynthesis [90; 91]. For example, some coatings can filter or block certain wavelengths of light, which can affect photosynthesis and other biological processes [89]. Greenhouse cover plays a crucial role in the efficient transmission of sunlight, a process measured by transmittance. This essential parameter indicates the percentage of sunlight that can pass through the roofing material [90; 92]. At the same time, proper thermal insulation is essential to maintain the heat needed for crop development. As solar radiation reaches the surface of the greenhouse cover material, some fractions of this radiation are absorbed, others are reflected, and the remaining portion is transmitted through the cover into the greenhouse, as illustrated in Figure 5. The selection of materials with optimal transmittance properties allows the entry of light necessary for plant growth, while minimizing heat loss, contributing to energy efficiency [93]. There are several types of roofing materials available for greenhouses, each with its own profiles for transmittance, thermal insulation, durability, and cost. Glass, for example, offers high transparency and longevity. Low-E glass and integrated photovoltaic glass are innovations that maintain the transparency necessary for photosynthesis while generating energy. Polymeric plastics, such as polyethylene (PE), polycarbonate (PC), and ethylvinylacetate (EVA), are valued for their lightness and cost-effectiveness. The durability and UV resistance of these materials have been improved with additives and treatments [90; 94; 95]. \begin{table}
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**Study Title** & **Purpose of the Study** & **Methodology Used** & **Main Results** \\ \hline A combination of agricultural and energy purposes: Evaluation of a prototype of PV greenhouse tunnel [81] & Evaluate the performance of a PV greenhouse prototype for agricultural and energy generation & Analysis of the indoor microclimate and energy production of a PV greenhouse tunnel & There is a consistency in shading, attributed to the curvilinear shape of the greenhouse, with virtually constant shading within it from March to September during the day. In the other months, shading alternated between the inside and outside of the tunnel greenhouse. With the photovoltaic system used, the shading did not exceed 40\% throughout the year. & There is a consistency in shading, attributed to the curvilinear shape of the greenhouse  
Thermal insulation is vital for reducing heat loss and minimizing heating costs. Materials such as multi-wall polycarbonate and polyethylene films with air bubbles or insulating foams can be used to improve thermal performance [40]. Rock wool, polystyrene, and insulating foams are commonly used to improve heat retention, which is essential in cold climate regions [96; 40; 97]. Greenhouse covers should have high levels of transparency to visible light and low permeability to infrared radiation. It is important that they maintain their clarity and do not suffer significant reductions in light transmission over time, thus ensuring an extended lifespan [98; 99]. In addition, they must offer robustness against weather conditions, such as gusty winds, to ensure durability and protection of crops [29; 100; 101].