A rooftop array on a livestock building sits in a chemically different environment from one on a warehouse fifty metres away, and the difference is not visible in a photograph. It comes out of the building. Ammonia released from manure and urine accumulates in and around housing for poultry, pigs and cattle, and it attacks some of the materials a standard solar specification assumes are fine.
This guide covers what is actually at risk, why a salt spray result does not answer the question, and what to ask for instead. It is the companion to our guide on coastal and industrial corrosion; the two environments are different problems and the specifications are not interchangeable.
Why livestock buildings are a different environment
Three factors combine, and the third is the one that catches people out:
- Ammonia in the air. It is generated continuously by the breakdown of waste, and concentrations are highest where ventilation is poorest.
- Persistent moisture. Housing is kept warm and humid, and the air leaving it is damp as well as ammoniacal.
- Ventilation outlets. Fans discharge that air somewhere, and the place they discharge it is often directly across the roof. An array positioned in the exhaust path receives a far higher dose than the ambient level would suggest.
That last point is a layout decision. Two identical buildings with identical equipment can have very different outcomes depending on where the fans discharge and where the array sits relative to them.
What ammonia attacks
The material list is different from the one for a coastal site, and that is the practical reason not to reuse a coastal specification:
- Copper and copper alloys. Ammonia attacks copper readily. Anything copper in the current path — conductors, terminations, connectors, busbars — needs to be either protected or specified out.
- Zinc coatings. Standard hot-dip galvanising is the default for mounting steel, and ammoniacal environments are hard on zinc. A galvanised structure that would be entirely adequate on a distribution centre can deteriorate quickly here.
- Some polymers and elastomers. Sealants, grommets and cable sheathing vary in their resistance, and the failures are slow: a seal that hardens, a grommet that cracks, moisture getting in somewhere it did not before.
- Module materials. The frame, backsheet and junction box are all exposed, and the junction box is both exposed and electrically critical.
Why a salt spray result does not answer this
This is the most common specification mistake on agricultural projects.
Salt mist testing and ammonia testing are different tests for different chemistries. Chloride attack and ammoniacal attack proceed by different mechanisms and affect different materials — a coating that performs well in one is not thereby qualified for the other. There is a dedicated ammonia corrosion test for photovoltaic modules, separate from the salt mist standard; the specific conditions, duration and acceptance criteria belong in the test report for the model you are buying.
So the useful question is not is this corrosion resistant but has this been tested for ammonia, to what method, and can I have the report. A supplier quoting a salt spray figure has answered a question you did not ask.
"Corrosion resistant" is not a specification
Three things to convert a phrase into something enforceable:
- The environment, stated. What the equipment will be exposed to: agricultural housing, exhaust path or not, and the cleaning regime.
- The test method, named. Ammonia corrosion testing for modules, and the relevant coating specification for steel.
- The evidence, supplied. Test reports and coating data sheets, with the order rather than after it.
Mounting structure and fasteners
This is where agricultural projects most often go wrong, because the default specification is a galvanised structure and the default assumption is that galvanised is enough.
- Coating specification. Ask what the coating is specified for, not what it is. Where galvanising is marginal, the alternatives are higher-specification coatings, stainless fasteners, or aluminium structure — and each has a cost and a compatibility question attached.
- Fastener material. Fasteners are the first thing to seize and the first thing to stain. On an agricultural roof they should be specified alongside the structure, not selected by whoever is fitting it.
- Dissimilar metals. Where aluminium and steel meet, or where stainless meets galvanised, the interface needs to be detailed. Ammoniacal moisture is a good electrolyte.
Our mounting structure selection guide covers how the choice is made by roof covering and foundation; this section is the amendment to it for farm buildings.
Electrical equipment
Three items worth checking specifically:
- Enclosure rating and material. Combiner boxes, inverter enclosures and isolators need an ingress rating appropriate to a damp, dusty, wash-down environment — and the gasket material needs to survive it.
- Any copper in the current path. Terminations and connectors are the points to check. Where copper is present, it needs protection appropriate to the environment.
- Cable sheathing. Standard sheathing is not specified for this. Confirm the cable is rated for the environment rather than assuming it.
The cabling, protection and enclosure items are listed in the balance-of-system buying guide; for an agricultural site, treat the environmental rating as a specification line rather than a footnote.
Ventilation, soiling and cleaning
Two operational points that are decided at design:
- Keep the array out of the exhaust path where you can. This is the single highest-leverage layout decision on a livestock building, and it costs nothing at design stage.
- Dust and moisture together make a more aggressive medium than either alone. Deposits on the module surface hold moisture against the frame and the backsheet. A defined cleaning interval is part of the corrosion specification, not just a performance one — and the cleaning agent matters, because the wrong one adds to the problem.
What to specify
Reference table
Swipe horizontally to view all columns →
| Item | What to specify | What goes wrong if it is left open |
|---|---|---|
| Environment | Agricultural housing, and whether in the exhaust path | A coastal or generic spec applied to a different chemistry |
| Module test | Ammonia corrosion testing, with the report supplied | A salt spray figure answering the wrong question |
| Structure coating | Named coating specification for the environment | Default galvanising that deteriorates early |
| Fasteners | Material specified with the structure | Seized fixings and staining within the first years |
| Copper in the path | Identified and protected, or specified out | Terminations corroding at the connection |
| Enclosure rating | Ingress rating and gasket material for wash-down | Moisture in enclosures that were rated for a warehouse |
| Cable sheathing | Confirmed rated for the environment | Sheathing degradation over time |
| Cleaning regime | Interval and agent, defined | Deposits holding moisture, or a cleaner adding to it |
How we supply
We supply photovoltaic modules, mounting structures, inverters, storage and distribution equipment, with the manufacturer’s documentation package. Tell us the building type and whether the array will sit in a ventilation discharge path, and we will specify against that rather than against a generic outdoor environment.
Two things we will not do. We will not quote a service life for a given environment — that depends on the concentration, the moisture, the cleaning regime and the equipment combination, and a number given without them would be an assumption. And we will not assume that a specification written for a coastal site transfers across; the two environments fail different materials first.
Where the array is going onto an existing building, the roof condition comes first — the sequence is in our guide to roof life and roof warranty, and on an agricultural building the roof has usually had a harder life than a commercial one. For the maintenance side, our plant operations and maintenance guide covers inspection intervals.
BUYER CHECKLIST
Buyer considerations for this scope
Ask for the ammonia test, not the salt spray figure
They are different tests for different chemistries. A coating or module qualified against chloride attack is not thereby qualified for ammoniacal attack. Name the test method you want, and ask for the report to travel with the order rather than being produced if something fails.
Specify fasteners with the structure, not after it
Fasteners are the first item to seize and the first to stain, and on an agricultural roof the default choice is often made by whoever is fitting it. Material and coating belong in the same specification line as the structure itself.
Check the array against the fan discharge path
It is the highest-leverage layout decision on a livestock building and it costs nothing at design stage. Equipment specified for the ambient level can be under-specified for a position directly in the ventilation exhaust.
PRACTICAL ANSWERS
Questions buyers ask about this
Can I use the same corrosion specification as a coastal site?
Not without checking it. Salt mist and ammonia are different chemistries that attack different materials — chloride attack and ammoniacal attack proceed by different mechanisms, so a coating that performs well in one is not thereby qualified for the other. There is a dedicated ammonia corrosion test for photovoltaic modules, separate from the salt mist standard.
Is hot-dip galvanised mounting structure enough on a farm building?
It depends on the dose, and it is worth asking rather than assuming. Ammoniacal environments are hard on zinc coatings, and a galvanised structure that would be entirely adequate on a distribution centre can deteriorate quickly in or near livestock housing. Where galvanising is marginal, the alternatives are higher-specification coatings, stainless fasteners or aluminium structure.
Does a salt spray test result tell me anything useful here?
It tells you about chloride resistance, which is a real property but a different question. The useful question for an agricultural site is whether the equipment has been ammonia corrosion tested, to what method, and whether the report can be supplied. A supplier quoting only a salt spray figure has answered a question you did not ask.
Why does the ventilation layout matter so much?
Because fan outlets discharge air with the highest ammonia concentration, and they often discharge across the roof. An array sitting in that exhaust path receives a far higher dose than the ambient level suggests — two identical buildings can have very different outcomes purely from where the fans discharge relative to the array.
EXPLORE FURTHER