Solar Inverters UK

A solar inverter converts the direct current your panels produce into the alternating current your house runs on, and the type you get shapes three separate decisions: shade handling, battery readiness, and grid paperwork. The Energy Saving Trust puts it simply: "The direct current passes through a solar inverter to turn it into alternating current (AC) electricity. You need AC electricity to run your household appliances." Without it the panels make electricity nothing in your home can use.

It is also the component most likely to fail before the panels do, and the one homeowners know least about at the point of signing. Everything below was verified on 14 August 2026 against the Energy Saving Trust, the MCS solar PV installation standard MIS 3002, the Energy Networks Association and HMRC VAT Notice 708/6.

The four ways a UK solar system is wired

There is one inverter job and four common ways of doing it. Almost every domestic quote in the UK is one of these.

• A string inverter. One box, usually in the loft or on a utility room wall, wired to all the panels in series. It is the long-standing default and the simplest thing that works. The catch is in the wiring: panels in a string interact, so a single heavily shaded panel drags on the rest of that string.
• A string inverter plus optimisers. A small device fitted behind each panel, working with a central inverter. The Energy Saving Trust describes what they buy you: "Solar optimisers help improve the overall performance of your solar panel system. So, if one panel is shaded, it doesn't impact how much electricity the other panels can generate."
• Microinverters. One small inverter per panel, mounted on the roof, converting to AC at each panel rather than in a single central box. Each panel then runs independently. There is no central inverter to fail and take the whole system with it, but there are a dozen or so units sitting under the array where replacing one means going back on the roof.
• A hybrid inverter. A single unit that handles both the panels and a battery. If a battery is on your list, this is the configuration that matters, and it is worth reading the next section carefully because it changes your grid application.

The Energy Saving Trust is blunt about when optimisers are worth it: "If your roof doesn't have shading, optimisers won't help you generate more electricity. But having an optimiser gives you extra opportunities to monitor your system's performance." That is the honest test for the whole per-panel category. Per-panel electronics solve a shade problem. If you do not have a shade problem, you are buying monitoring detail rather than electricity.

Which setup suits your roof

Start with shade, then batteries, then everything else. The decision is usually settled by the first two.

• One clean, unshaded roof plane. A plain string inverter does the job and costs the least. Per-panel electronics add cost for output you were going to get anyway.
• A chimney, a dormer, or a neighbour's tree over part of the array. This is what optimisers and microinverters exist for. Ask the installer to quantify the shade loss both ways rather than accepting the upgrade as a default.
• Panels split across two roof faces. Different orientations generate on different curves, which is awkward for a single string. Either a multi-string inverter or per-panel electronics handles it. Our guide to which direction solar panels should face covers what each aspect actually yields.
• A battery now, or a battery later. A hybrid inverter takes both jobs in one unit. If you are undecided, ask what adding storage in five years would involve with the inverter being quoted, because the answer is sometimes a second inverter. Our solar battery storage guide covers the cost side.

The inverter, not the panels, sets your grid paperwork

The threshold that decides which grid application your installer files is measured on AC output, which is the inverter's rating, not the kWp of panels on your roof. This is the single most misunderstood thing about inverters in UK domestic solar, and it costs people weeks.

The Energy Networks Association sets the national rule: "A generator with a capacity less than 3.68kW/phase then EREC G98 applies" and "A generator with a capacity greater than 3.68kW/phase then EREC G99 applies." G98 is the fit-and-notify route. G99 means applying to your network operator and waiting for approval before anything is connected.

MCS requires its certified installers to follow the same thresholds. MIS 3002, the solar PV installation standard, states at clause 3.1.5 that the contractor must follow the requirements "In Engineering Recommendation (EREC) G98 for installations up to and including 16 A per phase", "In EREC G99 for installations exceeding 16 A per phase", and "In EREC G100 where the export of power is to be limited".

Then comes the note that catches people out. MIS 3002 spells out exactly how that 16A is counted:

"the 16 A per phase threshold is the total aggregated AC output of all generators. For example, a 3kW solar PV system and a 3kW electrical energy (battery) storage system are connected in parallel to the same single-phase AC supply, gives a combined maximum theoretical output greater than 16 A. In this case EREC G99 applies."

Read that example again, because it is the practical trap. A 3kW solar system on its own sits comfortably inside G98. Add a 3kW battery and the aggregate crosses the line, so the whole job becomes a G99 application even though neither component would have triggered it alone. If you are adding storage to an existing system, or buying solar and a battery together, the inverter configuration is what determines whether your installer is filing the quick form or the slow one.

There is a third route worth knowing about. Where export needs to be capped to stay inside a limit, EREC G100 applies. The ENA describes it as "Technical Guidance for Customers' Export and Import Limitation Schemes", and it is how a larger array can be installed on a constrained connection: the inverter is configured to limit what it pushes back to the grid. Our full guide to G98 and G99 walks through both processes and the per-network differences, including Northern Ireland, where NIE Networks operates its own G98/NI and G99/NI rules on a separate process.

One point on responsibility that rarely reaches homeowners. The ENA states that "Compliance is the responsibility of the customer who is quite often, but not always, the owner of the generation" and that owners "are required to make sure that generation equipment they purchase and install on their premises complies with the law". In practice your MCS installer handles the notification, and MIS 3002 clause 3.1.6 requires it of them, but the legal duty sits with you. That is a good reason to keep the paperwork.

How UK inverters are actually regulated

Panels and inverters go through different UK compliance systems, and knowing which is which tells you what to ask for.

For the panels and the mounting kit, the route is MCS product certification. MCS says certified installers "use MCS certified products, including solar panels and mounting kits", and you can look up any model in the MCS Product Directory.

For the inverter, the relevant register is the ENA's type test register, which records manufacturers' declarations that a unit meets EREC G98 or G99. The ENA runs it as a repository "where equipment manufacturers can submit information about their products and make their own declarations of compliance with EREC G98 or EREC G99", and it publishes each entry with its compliance status, manufacturer, model, category, capacity in kW and phase. For smaller units the register is compulsory: the ENA states that EREC G98, "which applies to generation equipment rated less than 3.68kW/phase, requires that manufacturers must always lodge their declarations of full compliance in the ENA LCT Register."

Above that threshold it is not mandatory. The ENA notes it "is not mandatory for manufacturers of generation products with a capacity greater than 3.68kW/phase to use this register to declare compliance information about their generation products there", so an absence from the register is not automatically a red flag on a larger inverter. Ask the installer for the manufacturer's declaration of compliance instead.

Worth knowing alongside that: MIS 3002 requires solar PV systems to be designed and installed in accordance with the 2nd Edition of the IET Code of Practice for Grid Connected Solar Photovoltaic Systems, and states that where requirements conflict, "the latest version of BS 7671 shall take precedence". BS 7671 Part 7-712 is the section covering solar PV supply systems specifically.

Inverter size is not panel size

Your quote carries two different capacity numbers and they do not have to match. The array is rated in kWp, the peak DC capacity of the panels under laboratory test conditions. The inverter is rated in kW of AC output. The second number is the one the grid threshold is measured against.

Panels almost never hit their kWp rating on a UK roof, because that rating assumes lab conditions your weather does not supply. We cover why in our guide to solar panel efficiency. So an inverter rated a little below the array's peak DC figure is a normal design choice rather than a mistake, and it is one of the levers an installer uses to keep a system inside G98.

What matters is that you know both numbers and why they were chosen. Two questions do it:

• What is the inverter's rated AC output, and does that keep us inside G98? If the answer is no, ask what the G99 timeline looks like before you agree a fitting date.
• If we add a battery later, what happens to that number? The MIS 3002 example above is the reason to ask now rather than later.

What an inverter costs, and the VAT trap on buying one yourself

No UK primary source publishes a separate figure for what a domestic solar inverter costs, so we are not going to invent one. The inverter is bundled into the installed system price on every quote you will see. The Energy Saving Trust benchmarks a typical 4.5 kWp domestic system at around £7,600 installed, and MCS puts the average certified domestic system in 2025 at just over £7,000 on its own data dashboard. The inverter sits inside those figures. Ask for it as a line item if you want to compare two quotes properly, and see our full breakdown of solar panel costs for what else should be in there.

The VAT position, though, is precise and worth understanding because it can cost you real money.

HMRC's VAT Notice 708/6 lists solar panels among the energy-saving materials qualifying for the zero rate, and its definition at section 2.11 explicitly names the inverter: the relief covers "photovoltaic (PV) panels with cabling, control panel and AC/DC inverter". So the inverter in a supply-and-install job is inside the 0% rate.

Buy the unit over the counter and the position reverses. Section 2.3 of the same notice is unambiguous: "if you supply energy-saving materials without installing them your supply will be standard-rated. For example, the sale of energy-saving materials by a retailer is always standard-rated." That means 20% VAT on an inverter you buy yourself, against 0% on one your installer supplies and fits.

The zero rate is also time limited. VAT Notice 708/6 covers installations to 31 March 2027 and states that "From 1 April 2027 onwards, supplies of installations of energy-saving materials will revert to the reduced rate of VAT of 5%". Note that is 5%, not 20%, a distinction plenty of sites get wrong. Our guide to VAT on solar panels works through the full rules, including what this means for a replacement inverter years from now.

The inverter is the part that ends first

Budget for replacing it at around year 12. The Energy Saving Trust is direct: "Your solar panels should last 25 years or more. But if you have a solar inverter, you need to replace this after around 12 years."

The warranty gap is where people get caught. The Trust says "Most inverters have warranties of five years as a minimum, which you can often extend by up to 15 years", then adds the line that should shape the decision: "You might find that a 15-year warranty costs almost as much as a replacement inverter, so consider it carefully." Price the extension against a replacement unit rather than assuming the extension is good value.

Monitoring is the other thing to settle at quote stage, because a dead inverter you do not notice costs you far more than the part. The Trust notes that "Some inverters have online monitoring functions and can warn you by email if the system fails", and that your installer should leave written maintenance details including "details of the main inverter fault signals and key troubleshooting guidance". Our guide to how long solar panels last covers the replacement economics, the warranty position and the VAT on a mid-life swap in full.

What to check on the quote

Five questions, all of which should get a straight written answer.

• Make, model and rated AC output. Without these you cannot check anything else, including whether the job is G98 or G99.
• String, hybrid, optimisers or microinverters, and why this one for my roof. The answer should reference your shading and your battery plans, not a product tier.
• Is it G98 or G99, and who files it? MIS 3002 clause 3.1.6 puts the notification duty on the MCS contractor. Get the timeline in writing if it is G99.
• What is the inverter warranty, what does an extension cost, and what would a replacement unit cost today? Compare the last two directly.
• How will I know if it stops working? If the answer is a display in the loft you will never look at, ask about monitoring with alerts.

None of this needs technical knowledge to ask. It needs the model number and a willingness to wait for the written answer, which is also a decent test of the installer. Our guide to choosing a solar installer covers the rest of that conversation.

Solar inverters: frequently asked questions

Figures and quotations on this page were verified against the Energy Saving Trust, MCS standard MIS 3002, the Energy Networks Association and HMRC VAT Notice 708/6 on 14 August 2026. Grid connection rules, standards and VAT treatment change, and network operator processes differ between regions and in Northern Ireland. Check the linked primary sources before making a decision.