## 2 Construction Aspects for Energy Performance Improvement
### Greenhouse Construction
#### 2.2.2. Covering and Insulation Material for Greenhouses
Each greenhouse roofing material has specific limitations that influence its selection: polyethylene plastic, although economical, has limited durability and poor thermal insulation, requiring frequent replacement; polycarbonate offers better insulation and strength but with a higher cost and susceptibility to scratches that can affect light transmission; glass provides excellent transparency and durability, but it is expensive, heavy, and fragile, requiring robust support structures; air-inflated double-layer polyethylene films improve thermal insulation, but require continuous maintenance of the inflation system and are vulnerable to punctures and light-diffusing films distribute light evenly, but are more expensive and can suffer UV degradation. Choosing the ideal material depends on a balance between cost, durability, plant needs, and local climatic conditions, requiring careful evaluation of pros and cons [95; 102; 103]. Advanced materials, such as aerogels and nano-structured membranes, are being researched for their superior insulating properties and ability to selectively filter light spectra, optimizing transmittance for plant-specific needs [104; 105]. Light-diffusing covering material can promote more uniform plant growth, avoiding spots of intense light that can cause stress or burns [106]. The graph in Figure 6 is a visual representation of the transmissivity of light through different materials used in greenhouse roofs [7]. Transmissivity is expressed as a percentage, indicating the fraction of incident radiation that is transmitted through the material. With 86% transmissivity, the glass is highly transparent, allowing a large portion of sunlight to pass through, which is beneficial for most greenhouse applications. With a transmissivity  
Figure 5: Interactions of solar radiation with a material. The diagram illustrates the three fundamental processes: reflection, absorption, and transmission. Incident solar radiation is partially reflected off the surface, absorbed by the material and transmitted through it. of 81%, slightly lower than glass, Acrylic is known for its strength and clarity, although it filters a little more light. With 77% transmissivity, polycarbonate allows less light to pass through compared to glass and acrylic but offers advantages such as durability and impact resistance. Glass fiber-reinforced plastic panels have 82% transmissivity, a middle ground between polycarbonate and acrylic, combining transparency and strength. With 90% transmissivity, polyethylene is a highly translucent material, making it an economical and efficient option for light transmission in greenhouses. The choice of roofing material for a greenhouse depends on a balance between the amount of light desired to optimize plant growth and other material properties such as weather resistance, durability, and cost. The review article of [PERSON] et al. [90], discusses the development and use of nano and microscopic materials to improve thermal insulation in greenhouses while maintaining visible light transmission crucial for photosynthesis. These advancements aim to minimize heat loss while generating significant energy savings. The analysis includes materials such as glass, plastic films and sheets, as well as additives such as fillers and dyes. Graphene, fullerene and phase transition materials (PCMs) are noteworthy for their potential to insulate against radiation, suggesting their applicability in greenhouse covers. The review categorizes advances in semi-transparent photovoltaic materials and zinc oxide-based films, emphasizing their thermal insulation and light transmission properties. The development of new roofing materials for greenhouses is anticipated, despite climate concerns. The study concludes by highlighting the positive impact of these technologies on sustainability, energy efficiency, reduction of \(CO_{2}\) and agricultural productivity, also highlighting the economic benefits, such as the reduction of operating costs through the use of PCMs to stabilize temperatures.