Photovoltaic greenhouse - economic structure, advantageous for the photovoltaic generator and for agricultural production

The balance point between the need to create a perfect environment for the crop and a durable, economical, solid and performing structure for the photovoltaic generator

Greenhouses are becoming more and more concentrates of technology. From the simple protected tunnel we have progressively passed to greenhouses that tend to create closed environments, where the seed enters and the finished product exits. This type of systems must comply with some fundamental parameters, the most important are:

  1. durability of the covers;
  2. an intrinsic structural strength;
  3. protection of steel structures;
  4. a perfect harmony between the integrated technological systems;
  5. and last but not least, they must be cheap.

In a greenhouse the main elements that influence the duration over time are: foundations and steel structure, and the roof panels. 

As for the latter element, when possible we prefer to make roofing in polycarbonate, of the clear type, capable of passing light radiation up to 90% such as glass (see the article where glass is compared with polycarbonate).

It is obvious that the installation of glass roofs can have advantages but also intrinsic fragility, while polycarbonate has characteristics such as to make it practically equal to itself at least up to 20 years (due to its high resistance to UV rays and not on the other hand it generates good protection from UV radiation) and from the point of view of light transmission while at the impact angle of 90 ° the glass and polycarbonate panels show a similar light transmission; at low angles of incidence 0.8mm corrugated polycarbonate transmits nearly 50% more light.

It is also easy to install and replace and prevents condensation dripping.  

There steel structure of the greenhouse must follow a design process that can be schematized as follows:

  • choice of materials;
  • structural pre-dimensioning;
  • structural analysis, to evaluate the effects of external actions on the same structure; 
  • verification of the resistance where the resistant stresses must be greater than those acting;
  • verifies that the deformations of the structure are lower than the limits established by the regulations.

In general, a structural system can be broken down into increasingly simple systems, up to the individual components. Therefore a harmonic system where everything, even the smallest fixing element, must meet specific criteria of:

  • reliability, must be able to withstand the loads acting during execution and operation;
  • robustness, in the event of exceptional events, the structural damage must not be disproportionate to the triggering causes;
  • duration, the physical and mechanical characteristics must remain unchanged for the entire useful life of the work;
  • precaution, the materials and components must have certain geometric and mechanical characteristics and in particular in the case of steel, this is guaranteed by the CE marking of the product.

National and European regulations consider the following structural steel classes for the production of hot rolled open section sections (NTC 2008, table 11.3.IX; UNI EN 1993, table 3.1):

  • S 235 (Fe 360)
  • S 275 (Fe 430)
  • S 355 (Fe 510)
  • S 460

The value after the S (steel) indicates the characteristic yield stress. The denomination that the same steels had in previous regulations is indicated in brackets.

There hot dip galvanizing. It is of fundamental importance to guarantee the functionality, safety and usability of steel structures over time.

Rust, if left free to act, reduces the useful life of the steel and deteriorates its characteristics. The anticorrosive treatment with the best cost / protection / durability ratio is hot dip galvanizing.

The anticorrosive action offered by hot-dip galvanizing is both passive and active and has the ability to protect the internal surfaces of a product as well. During the galvanizing phase a real iron-zinc alloy is formed so that the protective layer remains firmly adherent to the steel.

These and other features are unique to hot dip galvanizing. A lasting protective strategy such as galvanizing, involves essential savings in terms of natural and energy resources as well as economic ones.

ISO 1461 (international standards for hot dip galvanizing) define the minimum thicknesses necessary to consider the protective zinc layer compliant. The average thickness of the coating must be at least 45 microns (steel thickness <1.5mm); at least 55 microns (steel between 1.5 and 3.0mm); at least 70 microns (steel between 3.1 and 6.0mm); at least 85 microns (steel> 6mm) to have last up to 80-100 years.

The photovoltaic generator is completely confined from the plant engineering point of view compared to greenhouse plants, but its presence can bring great benefits to agricultural production.

In some cases it is necessary to integrate the light radiation for some crops with lamp systems, mostly led, in this case the farm can draw energy directly from the generator or storage systems with significant savings in the bill.

In indoor cultivation systems the presence of a photovoltaic generator can be an important synergistic element that generates an extraordinary compatibility of the agricultural project with the same photovoltaic generator.

There are other synergies between plant systems, such as the ability to power pump systems, from irrigation to heat exchangers, etc.

The power / weight ratio is a parameter commonly used to compare the performance of vehicles or engines of cars, motorcycles, etc.  It is defined as the ratio between the power of the engine and the weight (or rather the mass) of the vehicle (or sometimes the ratio between power and weight of the engine is indicated), the weight / power ratio is of course its inverse. 

This ratio can be an excellent indicator between the installed power on the photovoltaic greenhouse and the weight of the structure used to house it.

Below a calculation model which can provide an idea of how the structural data combine with other values, such as irradiation, shading or space allocated to the PV generator, efficiency of the photovoltaic modules etc. 

greenhouse efficiency
Eg. 1412 W / m² January
Ex. Mono 19%, Poli 20%, CUdTe 16%
Area occupied by the PV
Size of the PV generator
Number of Wp for the entire surface
Referred to the structure
Referred to the structure
Referred to the structure

This calculation module is a free service provided as is. By using the service, the user raises the website and the manager from any responsibility, implicit and explicit, deriving from its use. The website or the operator are in no case responsible for any inconvenience, damage and / or economic loss caused by the use of the calculation module.

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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