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Energy in greenhouses, a necessary source for productivity
Growing vegetables, flowers and ornamental plants in greenhouses is beneficial in many ways. In fact, plants that grow in structures with a controlled environment develop better. In greenhouses, lowering or raising the temperature and controlling humidity is done through ventilation, heating and humidification systems. However, this equipment requires a certain amount of energy and fuel to operate efficiently.
In order to reduce the input of electricity from external sources, and use renewable sources, the installation of solar panels can prove to be an effective solution to provide energy needed for climate control in greenhouses. In addition, photovoltaic technologies, are widely promoted by institutions in order to foster the green revolution.
Installing photovoltaic panels requires space
Considering the lack of adequate space to install photovoltaic panels on farms, especially in areas where arable land is scarce or very expensive, greenhouse roofs may seem like an ideal surface on which to install this energy-efficient equipment.
However, photovoltaic panels installed on the roof of greenhouses and nurseries will shade the surface below. The shade produced, will prevent direct sunlight from reaching the plants. This factor will most likely negatively affect their growth. Therefore, it is important to consider the various risk factors for plant health in these structures before proceeding with the installation of photovoltaic systems.
The importance of geometric design
Installing photovoltaic panels on the roof of greenhouses is possible, but only after careful geometric design. Arranging the panels in such a way that they do not excessively reduce the amount of direct sunlight entering the greenhouse is critical to crop productivity.
For example, researchers have shown how different geometric arrangements of PV modules affected the growth of a Welsh onion crop in a greenhouse.
The researchers analyzed the results of two types of greenhouses, one with PV panels arranged in a linear fashion, and the other with a checkerboard panel structure.
The linearly arranged panels achieved better energy yields, but garlic growth decreased dramatically. In contrast, the checkerboard method ensured an optimal supply of direct sunlight, with slightly lower, but still satisfactory, electricity production.
Another key factor is the orientation of the structure; for example, an east-west oriented structure will favor the entry of direct sunlight through the side walls (since in the morning and evening the sun is at a lower angle).
In what cases is shading necessary?
Therefore, the darkening of the greenhouse has a negative impact on the growth of most plants grown within it. As a result, this factor erodes the main purpose of greenhouses, which is to promote faster growth and improve crop productivity under controlled environmental conditions.
However, the installation of photovoltaic panels on greenhouse roofs creates ideal environmental conditions for the growth of certain types of crops.
In greenhouses designed for mushroom germination, a rooftop cover through solar panels is perfect, as they promote darkening of the structure, which is crucial for this type of production.
Dark leafy vegetables, such as spinach, Swiss chard, kale and collard greens, require a growing environment with less direct sunlight. Greenhouses for floriculture such as orchid, hydrangea, or cyclamen crops also require shading of about 75 to 90%.
For these crops, the installation of photovoltaic panels on the roof of the structure is a great way to shade the environment below and get clean energy to activate the various machines inside the greenhouse.
Future development prospects
In climates where summers are very hot, sunny and arid, crops inside greenhouses suffer from the excessive influence of sunlight. For this reason, temporary shade cloths are used, which can be easily removed at the end of the hot season.
The use of photovoltaic panels to shade the greenhouse can be an alternative solution to shading nets and paints. This method will help cool the greenhouse microclimate, especially when coupled with an efficient ventilation and humidification system.
Obviously, the concern of farmers lies in the fact that solar panels are not removable. For this reason, modern research is focusing on the development of variable systems, which allow to adjust the angle of the panels placed on the roof; according to the needs of the greenhouse plants.
Although the use of photovoltaic panels on structures intended for agricultural production still has some disadvantages, it is clear that future innovations will allow a wider dissemination of these systems.
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