What an Agricultural Greenhouse Photovoltaic Racking System Is
An agricultural greenhouse photovoltaic racking system is a support structure that carries solar modules on the same site as the greenhouse. Two arrangements are common. Modules can be integrated into the roof of the greenhouse itself, or mounted on free standing racking raised above the greenhouse frame so that the crop is never touched by the mounting system. In both cases the racking is the load path between the modules and the ground, so it must carry dead load, wind and snow, and transfer them safely to the foundation.
Because the racking stands in a warm, humid agricultural environment, materials and coatings matter as much as strength. Hot-dip galvanized steel to EN ISO 1461 and continuously zinc coated steel to EN 10346 are widely used, since the zinc layer protects the frame against condensation, irrigation water, fertiliser and ammonia from livestock. Aluminium profiles are also used for lighter roof-integrated systems, though the higher cost and the need to insulate connections between dissimilar metals have to be taken into account.
Multiple Use of the Same Land Area
The main attraction of the concept is that land is used twice. A greenhouse already occupies valuable ground and is often limited by land availability, land price or planning constraints, which makes it uneconomic to build a separate solar plant next to it. Mounting the photovoltaic system on the greenhouse or on racking above it means the same area produces crops and electricity.
No additional land is taken for electricity generation, and the foundations, access roads and grid connection can be shared.
The structure benefits from an existing perimeter, so security, drainage and site services are available at low additional cost.
Cables, inverters and mounting steel can be installed during a scheduled greenhouse build or refurbishment, avoiding a second mobilisation.
Where the farm already has a transformer and grid connection for pumping or cold storage, the extra capacity needed for the array is usually modest.
Electricity Generation, Cost Saving and Farm Income
A greenhouse farm is an energy consumer all year round. Ventilation fans, irrigation pumps, lighting, cold storage and sorting equipment all draw power, and in remote areas pumping may depend on diesel generators. A photovoltaic system on the greenhouse roof or racking reduces the electricity bought from the grid and lowers operating cost, with the strongest effect during the sunny season when irrigation and cooling demand is highest.
Where local rules allow, the array can also be connected to the distribution grid and surplus electricity exported, creating a second income stream alongside the crop. The output of an installation depends on local solar irradiation, module efficiency, tilt angle, row spacing and the amount of greenhouse shading that can be accepted, so the layout is normally sized from an irradiation study rather than from roof area alone. Combining the two activities also spreads risk: a poor crop season and a poor generation month rarely coincide exactly, which makes total farm income more stable than either activity on its own.
Effect on the Greenhouse Microclimate
Shading is often described only as a loss of light, but in a greenhouse it also lowers peak temperature and reduces evaporation inside the house. Both effects matter during hot spells, when excessive temperature stresses the crop and drives up water consumption.
Temperature: the modules intercept part of the incoming radiation, so the air temperature under the shaded zone rises less sharply at midday.
Humidity and irrigation: reduced evaporation lowers the water demand of the crop and the running time of pumps.
Weather protection: the racking and modules form a partial barrier against hail, heavy rain and strong direct sun, which limits mechanical damage to leaves and fruit.
Wind: module rows act as a shelter, so wind speed at canopy level and the associated mechanical stress are reduced.
The amount of shading must be matched to the crop. Leafy vegetables generally tolerate more shade than fruiting crops such as tomatoes or peppers, so the module coverage ratio, row spacing and tilt should be chosen together with an agronomist and, wherever possible, confirmed on a trial area before the whole greenhouse is equipped.
Racking Structure, Coating and Design Loads
The racking is an outdoor structure designed for a service life of decades, so the design loads and the corrosion protection system must be fixed at the start of the project rather than added later. Wind and snow actions are normally taken from EN 1991-1-4 and EN 1991-1-3, applied to the actual plan area of the greenhouse and to the module surface, including uplift on the modules and the effect of snow sliding off the array onto the greenhouse covering.
| Item | Typical specification | Reason for the requirement |
|---|---|---|
| Main racking steel | Q355B sections, or S250GD / S350GD coated steel to EN 10346 | Strength and stiffness with easy cold forming |
| Coating, batch galvanized | EN ISO 1461, average at least 70 µm at 3 mm to 6 mm wall and 85 µm at 6 mm and above | Long life in humid, fertiliser-bearing air |
| Coating, coated strip | Z275 to Z450 class to EN 10346 | Corrosion allowance matched to the exposure class |
| Fasteners and clamps | Zinc or stainless fasteners with insulating washers | Prevents galvanic corrosion between dissimilar metals |
| Module and array design | Modules qualified to the IEC 61215 series, array installation practice to IEC 62548 | Confirms electrical safety and mounting compatibility |
| Earthing and surge protection | Bonded frame and DC surge devices | Protects equipment and livestock area from fault current |
Detailing rules that are easy to underestimate include drainage of every low point so that water cannot stand in the section, separation of the steel from any copper or aluminium component, and cable routing that keeps the DC conductors out of standing water and off walkways used by workers.
Installation, Inspection and Maintenance
A correctly specified system needs very little routine work, but it does need a schedule. Inspections are normally carried out before the growing season and after the storm season, and afterwards following any exceptional weather event.
Structure: check the coating for scratches, chalking or white rust, and look for loose or distorted members and movement at the base connections.
Fasteners and clamps: verify torque values, and re-check clamps after the first season when thermal cycling has taken place.
Drainage: clear gutters, channels and any drilled drain holes so that water and plant debris cannot collect against the steel.
Electrical: inspect cable insulation, connectors and earthing bonds, and keep vegetation clear of the DC cabling.
Modules: remove dust, pollen and bird droppings on a schedule that suits local conditions, since soiling reduces output and shading by soiling is uneven.
Because the frame is protected by a zinc coating rather than by paint, there is no repainting programme and no need to dry out the greenhouse for maintenance painting. Local damage can be cleaned and repaired with a zinc-rich coating during a normal inspection visit, which keeps both cost and downtime low.
Frequently Asked Questions
Q: What is an agricultural greenhouse photovoltaic racking system?
It is a support structure that carries solar modules on the same site as a greenhouse, either integrated into the roof or on racking raised above the frame. It transfers module loads to the ground while allowing crops to be grown underneath or alongside.
Q: What are the main benefits for a farm?
Land is used twice, electricity is generated on site to cut running costs for pumping, cooling, lighting and cold storage, surplus power can be exported where regulations allow, and the combination of crop and energy income makes farm revenue more stable.
Q: Does the shading reduce crop yield?
Shading always reduces the light available, but it also lowers peak temperature and evaporation. Whether yield falls depends on the crop and the shade ratio. Leafy crops usually tolerate more shade, so the layout should be agreed with an agronomist and tested on a trial area first.
Q: Which material is used for the racking?
Hot-dip galvanized steel to EN ISO 1461 is the usual choice for structural racking, with continuously coated steel to EN 10346 used for lighter profiles. Aluminium is also used for roof-integrated systems, but connections between dissimilar metals must be insulated to avoid galvanic corrosion.
Q: What standards apply to the design?
Wind and snow actions are taken from EN 1991-1-4 and EN 1991-1-3. Hot-dip galvanized steel follows EN ISO 1461, coated steel follows EN 10346, and the photovoltaic side is designed in line with the IEC 61215 series for modules and IEC 62548 for array installation.
Q: How much maintenance does the system need?
Normally two inspections a year, one before the growing season and one after the storm season, plus checks after exceptional weather. Work covers the coating, fasteners, drainage, cabling and module cleaning, and local coating damage is repaired with a zinc-rich coating.