Solar Panel Warranty (UK): the Layers on a Farm Roof Install

The four layers

Module product warranty. A promise that the module is free from defects in materials and workmanship for a set period. It is the layer that pays for a delaminated laminate, a failed junction box or a cracked frame. Kiwa PVEL's 2026 reliability scorecard found 87% of manufacturers and 61% of bills of materials had at least one test failure, with delamination failures tripling year on year, so this layer is not academic.

Module performance warranty. A promise that output will not fall below a stated curve, usually expressed as a first-year allowance and an annual degradation rate thereafter. The curve is only useful if the document says how output will be measured, by whom, at whose cost and against what reference, which is where most performance claims founder.

Inverter warranty. A separate contract with the inverter maker. The published terms, as at October 2026: SMA gives a five-year standard warranty that can be extended to 10, 15 or 20 years at any time during the five years. Fronius ships string inverters with two years of Fronius Warranty Plus and, on registration at Solar.web within 30 months of dispatch, extends it to a choice of seven years of Fronius Warranty (materials only) or five years of Warranty Plus (materials, labour and transport); inverters up to 12.5 kW commissioned after 1 September 2023 receive ten years free, as five years Plus followed by five years materials-only. SolarEdge gives a twelve-year standard warranty on inverters, extendable to 20 or 25 years depending on model, with the extension bought within 24 months of shipment and covering the inverter only, not its communication accessories. Which inverter suits which building is on solar inverters for farm buildings.

Workmanship warranty. The installer's promise about the installation itself: fixings, waterproofing, cabling, commissioning. RC62 is blunt about why it matters: installation issues are the largest single cause of PV fires, and a 2017 BRE study found DC connectors, inverters and DC isolators behind 84% of them. A workmanship warranty is only as durable as the company giving it, which is where the insurance-backed version comes in.

Insurance-backed warranties

An insurance-backed warranty, often shortened to IWA or IBG, is a policy that pays for the workmanship guarantee if the installer ceases trading. It does not add to what the guarantee covers; it makes the guarantee survive the installer. For a farm contract the questions are whether the installer's guarantee is insurance-backed at all, which insurer underwrites it, for how many years and up to what sum, and whether the policy document is issued in the farm's name. A certificate from the underwriter is the evidence; a line on the quote is not.

What the independent testers say about module warranties

Kiwa PVEL's methodology note for the 2026 scorecard makes two points that belong in every warranty conversation. First, modules with the exact same model type can be manufactured from completely different bills of materials, and the industry's certification tests are typically not rigorous enough to identify the difference. Second, module warranties also often have shortcomings that leave site owners exposed to significant financial losses. The practical consequence is that the warranty is only as good as the specific bill of materials it is attached to and the UK legal entity standing behind it. How to compare the module itself is on solar panel comparison for farm roofs.

What keeps the cover valid

• Maintenance to the standard. RC62 says PV installations shall be serviced and maintained in accordance with the installer's instructions and BS EN IEC 62446-2:2020, with the schedule following the service contract, warranty conditions and performance guarantees, and it adopts the Solar Energy UK recommendation of inspection at least annually by a competent person.
• Records. NFU Mutual's PV programme asks for all records of periodic inspections, servicing and maintenance to be kept as the reference for future inspections. A warranty claim without a maintenance log is an argument.
• Registration deadlines. The Fronius extension requires registration within 30 months of dispatch; a SolarEdge extension must be bought within 24 months of shipment. Module manufacturers set their own windows. Diary them at handover.
• Compatible parts. IEC 62548 does not allow DC connectors from different manufacturers to be mated, and RC62 asks for spare compatible connectors to be held on site. A repair with the wrong connector is both a fire risk and a warranty argument.
• Cleaning and clearance. Bird droppings and debris under panels cause hot spots; a regular cleaning programme is what insurers expect, and what a performance claim will be measured against. Whether bird-exclusion kit fitted to an array affects cover is a question for the manufacturer, in writing: see bird proofing solar panels on farm buildings.

The handover documents to keep

RC62 refers documentation to the IET Code of Practice and BS EN 62446-1:2016, which sets the commissioning tests, inspection and documentation for grid-connected systems, and notes the handover pack may form the health and safety file required under CDM 2015. Keep the commissioning test certificate, the electrical installation certificate, the string test results, the as-built drawings, the inverter and module serial numbers, the warranty documents with their registration confirmations, the G99 acceptance letter and the operation and maintenance instructions. These are the same documents your insurer will ask for, which is set out on solar panel insurance for farm buildings.

Making a claim

1. Identify the loss from the monitoring portal: which string, from when, by how much. Export the data.
2. Check the maintenance log and the last inspection report, and commission a thermographic survey if the fault is not obvious.
3. Read the warranty document for the notice period, the notice method and who must be told; many require the installer to raise the claim with the manufacturer.
4. Notify in writing, with the serial numbers, the commissioning records and the evidence, and keep the defective part.
5. Ask in advance who pays for measurement, labour, scaffolding and shipping, and whether lost generation is covered. On most module warranties it is the replacement module only.

Farm arrays and the 50 kW line

MCS certification, and the consumer-facing protections that come with it, apply to installations up to 50 kW. A 100 kW grain-store roof or a 250 kW livestock site is a commercial contract, and the warranty layers above are whatever the contract says they are. That is not a weakness, it is a negotiation: the module and inverter terms are fixed by the manufacturers, but the workmanship warranty, its insurance backing, the maintenance obligations and the performance-measurement method are all contract clauses a farm can ask for. The certification question is set out in is MCS certification required for a farm solar install.

The figures on this page and where they come from

For what a complete farm system costs, from the government's installation data rather than quotes, see solar panels for farm buildings cost; for the head-term guide, solar panels for farm buildings.