Photovoltaic greenhouse - The correct amount of light and its distribution on the plane

Each crop needs solar radiation which in combination with temperature, humidity, air and water generates an ideal microclimate to thrive.

Our main source of energy is the sun, solar radiation is the form of energy that activates all the meteorological, physical and biological processes on the planet.

The sun produces electromagnetic waves with a wavelength between 0.3 and 30.0 µm. Plants use electromagnetic waves with a wavelength between 0.4 and 0.7 µm for photosynthesis (PAR), which roughly corresponds to the visible. As a result of all the phenomena of radiation dispersion in its journey from the sun to the leaves, which make up the plant cover, the photosynthetic efficiency, i.e. the ratio between the energy content of the biomass and the solar radiation available, is very low and varies in the our environments from 2 to 5%.

Plants can be classified into two large groups: heliophilous plants, which require a high intensity of light, and sciaphilous plants, which suffer from excess light. Cultivated plants are generally facultative sciaphilous.

For these reasons, the agronomic technique has the task of controlling the radiation regime of the crops, in fact by increasing the plant density the brightness is reduced and the accumulation of reserve substances is favored, also with a correct orientation of the rows, north-south. enlightenment is favored. These and other techniques contribute to the optimization of the radiation regime, for example: the position and exposure, the sixth of the plant, the control of the infesting flora, the shading, the tamping.

Another relevant agronomic aspect is the behavior of plants in relation to the duration of the period of solar radiation or photoperiod, in this case we have two groups of plants or those that pass to the reproductive phase when the lighting photoperiod does not exceed 12 hours a day ( among these the short days such as rice, chrysanthemum or tobacco and the neutral day ones such as tomato, potato, strawberry or bean) and those that pass in the reproductive phase when the lighting period exceeds 14 hours a day, the longi diurnal (including chard, clover, oats).

The benchmark relative to solar radiation is the Daily Light Integral which is defined as the total number of photons that affect per square meter in a day.

DLI is measured in units of mol / m² and each plant has a specific requirement of DLI for its growth. Values between 6-18 mol / m² / day are the most common, but can vary depending on the particular plant.

Therefore it is essential in the design phase to have a clear understanding of the crop project to optimize the structure of the photovoltaic greenhouse in order to provide the crop with the solar radiation necessary for it to thrive.

We see in the table below the values for some common crops to be done in the greenhouse. 

Lettuce14 – 16
Broccoli15 – 35
Tomatoes20 – 30
Peppers30 – 40
Cannabis30 – 45

So with the right tools, in terms of effective microclimate data and good design, a greenhouse structure can be created where the photovoltaic shading elements constitute an integrated improvement element if strictly related to the project crop and generate an optimal environment for the growth of plant. 

All requirements

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Calculate the DLI (Daily light integral) of the greenhouse you have in mind. Starting from the Italian geographical area concerned and knowing the limiting factors, in terms of the reduction of light radiation determined by the structure and material chosen as roofing, you can calculate the DLI of your project.

Energy green house photovoltaic rooftop solar
Naturae Plena

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