Solar Inverters for Farm Buildings: Types, Sizing and Warranty (2026)

Three types of solar inverters, and where each fits on a farm

String inverters take the DC output of several strings of modules and convert it to AC at the building's distribution board. They are the default for a farm roof: one or more three-phase units, each with its own maximum-power-point tracking inputs, mounted in a plant room or on a non-combustible wall. The design question is how many units, not which brand. A single large inverter is the cheaper installation; splitting the array across two or three units limits the output lost when one fails, which matters on a parlour or a poultry site with a continuous load.

Hybrid inverters add a DC-coupled battery input. They make sense only where a battery is part of the plan from the start; retrofitting storage to a plain string inverter is usually done with a separate AC-coupled battery inverter instead. The battery question on a farm is a separate decision with its own rules, covered on battery storage for UK farms.

Module-level power electronics, meaning optimisers or micro-inverters on each module, cost more but solve two farm problems. The first is shading and mixed orientation across several buildings. The second is fire safety: RC62 notes that module-level electronics can switch the DC side to extra-low voltage when the AC supply is disconnected, which is one of the two measures it lists for systems that cannot otherwise be designed as low voltage, and a direct answer to the question firefighters ask about live DC on a roof.

Sizing: the supply, the phase balance and the G99 line

The inverter's AC rating is bounded by the supply, not by the roof. The Engineering Recommendation G98 limit is 16 amps per phase: 3.68 kW on a single-phase supply or 11.04 kW across three phases. Up to that size the installer can connect and notify the distribution network operator afterwards. Above it, a G99 application has to be approved before the system is energised, and the operator can attach an export limit that caps what the inverter may push onto the network. A farm array is almost always above the line, so the inverter's type-test listing on the ENA register, its export-limitation capability and the G99 acceptance letter are the documents to ask for before anything is ordered. The process differs by operator; the practical steps are on UK Power Networks G99 connections and National Grid (NGED) G99 connections.

Two more sizing points. Balance the load across phases: a three-phase inverter does this by design; several single-phase units do not. And match the DC input windows to the strings: the installer should show the string voltage at the coldest design temperature sits inside the inverter's input range, because an undersized window is a nuisance trip in January and an oversized one is wasted hardware.

Siting and fire safety: what RC62 and insurers say about inverters

RC62 is the Joint Code of Practice for fire safety with PV installations, published in 2023 by the Fire Protection Association with RISCAuthority, MCS and Solar Energy UK and written for insurers and their clients. Its evidence on inverters is specific: a 2017 Building Research Establishment study found DC connectors, inverters and DC isolators accounted for 84% of PV-related fires. Its recommendations follow from that:

• Around 3% of the energy an inverter converts is turned into heat, so its location needs careful consideration, and obstructions or stored materials must not reduce its ventilation.
• Automatic fire detection should be installed in all areas inside buildings where inverters, isolators and distribution boards are located.
• Separate DC isolators should be eliminated wherever possible; many inverters now have integrated isolators.
• Whether the inverter's arc-fault circuit interrupter is acceptable, or a stand-alone one is needed, should be decided in the fire risk assessment.
• Where required, a fire-service switch in a prominent position should isolate the DC side remotely, and a sign of at least 100 mm by 100 mm reading "PV on the roof" should be displayed at the supplier's cut-out.

NFU Mutual's published risk management programme for roof-mounted PV asks for the inverter housing to be acceptably ventilated so the operating temperature is not excessive, for combustible materials and flammable liquids to be kept away from it, for the unit and any grid connection to be housed in or fixed to non-combustible construction, and for regular thermographic inspection. Dust from grain and straw, and ammonia in a livestock building, argue for a plant room or an external, shaded enclosure rather than a wall inside the shed. The wider fire picture, including grain-store dust and nesting birds, is on solar panel fire risk on farm buildings, and what the farm's insurer will ask to see is on solar panel insurance for farm buildings.

How long solar inverters last, and what the warranties say

The inverter is the component a farm should expect to replace. Marley's guidance puts replacement at five to 15 years depending on type and quality, and lists the reasons: wear on electrical components, heat, humidity and dust, electrical surges, and the thermal stress of normal operation. RC62 expects a PV system to have a design life of 30 to 35 years and asks that equipment be rated for that life rather than for the warranty period alone. Put together, that is one replacement in the array's life if the siting is good and two if it is not. The research behind that estimate is in how long do solar inverters last on a farm roof.

The manufacturers' published terms, as at October 2026, show how far standard cover falls short of that life:

• SMA: a five-year standard warranty, extendable to 10, 15 or 20 years at any time during the five years.
• Fronius: string inverters ship with a two-year Fronius Warranty Plus; registering on Solar.web within 30 months of dispatch extends it, with a choice of seven years' Fronius Warranty (materials only) or five years' Warranty Plus (materials, labour and transport). Inverters up to 12.5 kW commissioned after 1 September 2023 get ten years free, as five years' Warranty Plus followed by five years' Fronius Warranty.
• SolarEdge: 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.

Read what the term covers, not just its length: materials only, or labour and transport too, and what happens to the lost generation while a replacement is shipped. Those questions, and the module and workmanship layers that sit alongside, are set out on solar panel warranty.

Monitoring: the early-warning system

Every commercial inverter reports to an online portal, and RC62 treats that as a fire-safety measure as much as a performance one: live online monitoring and error indication provide early warning of potential problems on systems from domestic to utility scale, and it recommends that internet connectivity be arranged for every installation that lacks it. A string that drops out, a rising temperature alarm or a falling performance ratio is the first sign of a connector or isolator fault, which is exactly the class of fault the BRE study found behind most PV fires. The portal access should be handed over at commissioning in the owner's name, not the installer's.

The figures on this page and where they come from

Questions to put on the quote

1. Which inverter model, its ENA type-test listing, and whether it supports export limitation if the G99 acceptance comes back capped.
2. How many units, and what happens to the parlour or the shed if one fails.
3. Where it will be mounted, on what construction, with what ventilation and what fire detection.
4. Whether DC isolation is integrated, whether an arc-fault interrupter is fitted, and whether a fire-service switch is specified.
5. The warranty document itself: years, what is covered, who pays labour and shipping, and the registration deadline.
6. Who holds the monitoring portal login after handover.

The module side of the same decision is on solar panel comparison for farm roofs; the installer side on agricultural solar panel installers; and the cost of the whole system, from official data, on solar panels for farm buildings cost.

Inverter life is only one part of the answer farmers want; how long solar panels last on a farm roof covers the modules, the air in the building and the roof under them.