What Is a Solar Inverter? Types, Sizing and Costs

What Is a Solar Inverter? Types, Sizing and How They Work

A solar inverter converts the direct current (DC) electricity your solar panels generate into the alternating current (AC) your home runs on, at a nominal 230 volts in the UK. Without one, the electricity coming off your roof can't power a kettle, a heat pump or anything else in the house.

It's also the component most likely to need replacing before your panels do, and the one that decides how well the system copes with shading, how easily you can add a battery later, and what you can see on your monitoring app. Worth understanding before you sign anything.

On this page

• What is a solar inverter?
• How does a solar inverter work?
• The types of solar inverter compared
• What size inverter do I need?
• Do I need DNO permission?
• How long do inverters last?
• How much does an inverter cost?
• Solar inverter FAQ

What is a solar inverter?

It's the box that makes solar electricity usable. Panels produce DC, the grid and your appliances use AC, and the inverter sits between the two doing the conversion.

It does four other jobs at the same time:

• Tracks the maximum power point. Panel voltage and current shift constantly with light and temperature. The inverter's MPPT circuitry hunts for the combination that yields the most watts, several times a second.
• Matches the grid. Exported electricity has to match the grid's voltage, frequency and waveform, or the network operator won't allow the connection.
• Keeps things safe. Anti-islanding shutdown, earth fault detection, over-voltage protection and isolation are all built in.
• Reports. Generation data, export figures and fault codes all come from the inverter, which is what feeds your monitoring app.

A system is only as good as its weakest component, and the inverter is where cheap installations usually cut corners.

How does a solar inverter work?

Fast electronic switching, then filtering. Transistors inside the inverter switch the DC input on and off thousands of times a second, building a stepped approximation of an AC waveform, which is then filtered into the clean sine wave the grid requires.

Modern units are good at it. Peak conversion efficiency on a decent residential inverter sits around 97-98%, and the weighted "European efficiency" figure quoted on datasheets, which averages performance across a realistic spread of load levels, usually lands a percentage point or so lower. That's the number to compare, because your inverter spends most of a British year running well below its rated output.

Two design details matter more than the headline efficiency:

MPPT count. Each MPPT input tracks one string independently. A single-MPPT inverter on an east-west roof drags both halves of the array to a compromise operating point. Two MPPTs let each side do its own thing. Most domestic string inverters have two, some have three.

Start-up voltage. The array has to reach a minimum voltage before the inverter wakes up. On dull winter mornings a poorly matched string starts later and shuts down earlier than it needs to, which is one reason string design is an installer's job rather than a catalogue choice. Our guide to how solar panels work in the UK covers the generation side of the same process.

The types of solar inverter compared

Five options turn up in UK homes. Here's the short version before the detail.

Type	Best for	Typical UK installed cost	Typical warranty
String inverter	Simple, unshaded roofs, one or two orientations	£600-£1,200	10-12 years, often extendable
Power optimisers + string inverter	Partial shading on a budget	String inverter plus roughly £60-£100 per panel	12-25 years depending on brand
Hybrid inverter	New installs that include a battery	£900-£1,600	10-12 years
Microinverters	Shaded or complex roofs, mixed panel types	£1,500-£2,500 for a typical domestic array	20-25 years
AC-coupled inverter	Adding a battery to an existing system	Quoted with the battery	With the battery

Cost figures are UK market averages as of autumn 2026, sourced below, and your own quote will vary with brand, system size and access.

String inverters

A "string" is a row of panels wired in series. One wall-mounted inverter handles the lot, usually sited near the consumer unit to keep cable runs short.

For a string to work properly, the panels in it should share orientation, pitch, brand and power rating. Many string inverters have two or three MPPTs, so you can run a separate string on each, which is what makes an east-west roof workable without extra kit.

Pros

• Cheapest route to a working system, and the one most UK homes end up with.
• Proven technology with decades of field data behind it.
• One unit to monitor, update and eventually replace, all of it at ground level.

Cons

• The weakest panel in a string sets the pace. Shade, leaf litter or a failing module pulls the whole string down.
• Only system-level data unless you add optimisers, so fault-finding is slower.
• Strings need a minimum number of panels, which rules out very small arrays.

Microinverters

A microinverter is a small unit fitted behind each panel, converting DC to AC on the roof. Every panel then works independently, so a shaded one doesn't drag down its neighbours.

That makes them the natural answer for awkward roofs: multiple orientations, chimneys, dormers, or a mix of panel wattages. Enphase and APsystems are the names you'll see most often.

Pros

• Panel-level optimisation, so shading and soiling stay local to the affected panel.
• Per-panel monitoring, which makes faults obvious rather than mysterious.
• No high-voltage DC cabling inside the property.
• Easy to expand later, because you aren't constrained by one inverter's rating.
• Warranties of 20-25 years are normal, close to the life of the panels.

Cons

• Highest upfront cost, because every panel needs its own unit.
• Anything that fails is on the roof, so a replacement can mean scaffolding.
• More units means more potential failure points, although reliability is generally good.

Power optimisers with a string inverter

Optimisers also sit behind each panel, but instead of converting to AC they condition the DC and pass it down to a single string inverter. You get most of the panel-level benefit for less money.

SolarEdge is the market leader and pairs its own optimisers with its own inverters, delivering module-level MPPT with arc-fault detection built in. Tigo makes optimisers that work with most third-party inverters if you want to keep your inverter choice open. We fit SolarEdge systems regularly, including the SE5000H on domestic installs.

Pros

• Cheaper than microinverters with similar shading tolerance.
• Detailed per-panel data for fault detection.
• More design freedom on mismatched or multi-orientation arrays.

Cons

• Still dependent on the main inverter. If that fails, the whole array stops.

Hybrid inverters

A hybrid combines solar inversion and battery management in one unit. If you're installing panels and a battery together, this is usually the right architecture.

Because panels generate DC and batteries store DC, a hybrid keeps surplus energy in the DC domain when charging rather than converting it twice. That's a DC-coupled system, and it's slightly more efficient than the alternative. Surplus beyond what the battery can take goes to the grid under a Smart Export Guarantee tariff.

GivEnergy, Sunsynk, Solis, Growatt and Fox ESS all make hybrids for the UK market, and the Tesla Powerwall 3 has one built into the battery itself. If you've already got a Sunsynk, our guide to changing Sunsynk battery settings walks through the configuration screens.

Pros

• One unit, one app, one place to manage solar, battery, charging windows and export.
• Fewer conversion losses than an AC-coupled retrofit.
• Compact. Less wall space than separate solar and battery inverters.

Cons

• Single point of failure for both generation and storage.
• Battery choice is constrained to what the hybrid supports.
• Many domestic models cap out around 5-6kW, which limits array size before you need a second unit.
• Replacing a working string inverter with a hybrid just to add a battery rarely makes financial sense.

AC-coupled inverters

An AC-coupled inverter manages a battery on the AC side of the system, which means you can bolt storage onto an existing solar installation without touching the inverter that's already there. It's also how you run a battery with no solar panels at all, charging overnight on a cheap off-peak rate.

Integrated units such as the GivEnergy All-in-One combine the battery and its inverter in one cabinet. We cover the retrofit route in adding a battery to an existing solar system, and off-peak battery storage explains the tariff side.

Pros

• Works with almost any existing solar setup, whatever the inverter brand.
• Solar and storage fail independently, so one outage doesn't kill both.
• No need to scrap a perfectly good inverter.

Cons

• Extra conversion steps (DC to AC to DC to AC) cost you a few percent in round-trip efficiency.

Which type of solar inverter is right for your project?

Inverter choice follows from the kind of system you're building, so if you haven't yet settled on grid-tied, hybrid or off-grid, start there and come back. Once that's decided, work through it in this order:

1. Is any part of the roof shaded, or does it face more than two directions? If yes, you want microinverters or optimisers. If no, a string inverter is fine and cheaper.
2. Is a battery going in now? Then a hybrid. If it's going in later, a string inverter now plus AC coupling later keeps the door open.
3. Is the supply single or three-phase? Most homes are single-phase. Larger properties and commercial sites may be three-phase, which changes both the inverter and the grid connection paperwork.
4. Do you want backup power in an outage? That needs specific hardware, covered below.
5. How much do you care about per-panel data? Optimisers and microinverters give it, plain string inverters don't. Monitoring is how most faults get spotted in the first place.

What size solar inverter do I need?

Slightly smaller than your array, in most cases.

It sounds wrong, but panels almost never hit their rated output in UK conditions. A 5kWp array might peak at 4.2kW on a good June day and spend most of the year far below that. Sizing the inverter a little under the array, commonly somewhere in the range of 100-130% DC to AC, keeps it operating in its efficient band more of the time. Oversize the inverter instead and you've paid for headroom you'll use for a few hours a year.

There's a limit to it. Push the ratio too far and you start clipping real generation on bright days. The right number depends on your orientation, pitch and shading, which is why it comes out of the system design rather than a rule of thumb. How many solar panels do I need covers array sizing, and solar panel sizes explained covers the physical fit.

Do I need DNO permission for my inverter?

Yes, and it's based on inverter capacity, not panel capacity.

Your Distribution Network Operator governs what can connect to the local network under the Energy Networks Association's engineering recommendations. Systems at or below 16A per phase, which is 3.68kW, fall under G98 and can be notified to the DNO, in practice usually before the work. Anything above that needs a G99 application, which has to be approved before the system is commissioned. Applications go through the ENA's Connect Direct portal or the DNO's own system, and your DNO is set by your postcode rather than by who you buy electricity from.

This is why export limiting exists. A larger inverter can be configured to cap its export at 3.68kW so the installation stays inside G98 territory, while still generating freely for the house. Whether that's the right call depends on how much you export and how busy your local network is.

We handle the G98 or G99 submission as part of every installation, along with the MCS certificate you'll need for an SEG tariff.

Where does a solar inverter go?

Somewhere cool, dry, ventilated and reachable.

Inverters are lumps of power electronics, and heat is what kills them. A loft that hits 45 degrees in July is the worst common choice, and it's still where a lot of older systems ended up. A garage, utility room, plant room or a shaded external wall is better. The unit needs clearance around it for airflow and access for servicing.

They make noise, too. A faint electronic hum plus a cooling fan on larger models. Not loud, but loud enough that you'd notice it through a bedroom wall at night, so avoid mounting on the other side of one.

Battery siting is stricter than inverter siting. PAS 63100:2024 rules out lofts and bedrooms for domestic batteries, which often decides where the whole assembly goes.

Will my solar system work in a power cut?

Not by default, and this surprises people.

Grid-tied inverters are required to disconnect within moments of losing the grid. It's called anti-islanding, and it exists to stop your system back-feeding a supposedly dead network while an engineer is working on it. So in a standard installation, a power cut on a sunny afternoon leaves you with nothing.

Getting round it takes an inverter with Emergency Power Supply capability and, realistically, a battery. Depending on the unit, that gives you either a single backup socket or a changeover box that powers selected circuits. Not every hybrid supports it, and the ones that do vary a lot in how much load they'll carry, so specify it up front if outages matter to you.

How long do solar inverters last?

String and hybrid inverters typically last 10-15 years, against 25-30 years for the panels. Microinverters are usually rated for 20-25 years.

Expect one inverter replacement over the life of a solar system. Standard warranties run 10-12 years on most string and hybrid units, and many manufacturers sell an extension to 15 or 20 years, which is usually cheapest bought at the time of installation.

Signs yours is on the way out:

• Generation lower than the same month last year, with no new shading to explain it.
• Repeated fault codes, or the unit restarting itself.
• Louder fan noise, or a hot casing.
• Monitoring dropping out regularly.
• Any display of error codes the installer can't clear remotely.

Our guides to how long solar panels last and solar panel maintenance costs cover the rest of the system's upkeep.

How much does a solar inverter cost in the UK?

Around £600-£1,200 fitted for a like-for-like string inverter, £900-£1,600 for a hybrid, and £1,500-£2,500 for a microinverter system on a typical domestic array.

Those are market averages rather than our prices, and they move with brand, system size and how awkward the access is. Here's what sits behind them.

What you're buying	Hardware	Labour	Typical all-in
String inverter replacement, 3-4kWp system	£400-£800	£200-£400, 2-4 hours	£650-£1,100
Hybrid inverter (battery-ready)	Varies by brand	Included in install	£900-£1,600
Microinverters, around 12 panels	£960-£1,440	£600-£900	£1,560-£2,340

The string inverter figures come from Smart Solar Homes (£650-£1,100 all-in for a 3-4kWp like-for-like swap) and Solar Panels Funded (£400-£800 hardware plus £200-£400 labour, with loft access adding £50-£100). The same Solar Panels Funded analysis puts a 12-panel Enphase IQ8 system at £1,560-£2,340 all-in, with APsystems coming in cheaper. Hybrid pricing of roughly £900-£1,500 installed is reported by EcoAim, and Solar Panels Network puts the premium over a standard string inverter at about £400-£600.

Three things move the number more than brand does:

• Where the unit lives. A loft or a tight cupboard adds labour. A garage wall next to the consumer unit is the cheap version.
• Whether the wiring changes. A straight swap is a couple of hours. Moving the position, upgrading isolators or re-terminating strings is longer.
• Roof access. Microinverter work means scaffolding, which is why a single failed unit can cost more to reach than it does to buy.

As a share of a new installation, the inverter is a modest slice of the total. On a replacement it's most of the bill.

Zero-rate VAT applies to domestic solar and battery installations in Great Britain until 31 March 2027, after which it returns to 5%, and that covers the inverter as part of the installation (GOV.UK VAT Notice 708/6). A standalone replacement inverter on an existing system is treated differently from a full install, so ask for the VAT treatment in writing on any replacement quote.

For full-system numbers, see how much it costs to install solar panels and how much a solar battery costs.

Solar inverter FAQ

Can I add a battery to my existing solar inverter?

Usually yes, with an AC-coupled battery. It works alongside whatever inverter you already have, whatever the brand, and doesn't require replacing it. The alternative, swapping your string inverter for a hybrid, only makes sense if the existing unit is near the end of its life anyway.

What's the difference between a hybrid inverter and a normal one?

A standard solar inverter only converts panel DC to household AC. A hybrid does that and manages a battery as well, deciding when to store, when to discharge and when to export, all from one unit. In system terms that's the difference between a grid-tied and a hybrid installation, which the types of solar PV system guide sets out in full.

Do microinverters really produce more electricity?

On a shaded or multi-orientation roof, yes, because a weak panel no longer limits the rest. On a clean, unshaded, single-orientation roof the difference is small and rarely justifies the extra cost.

Can a solar inverter be installed outside?

Many can. Look for an IP65 or better rating and mount it out of direct sun, because a unit baking on a south wall runs hot and derates. An indoor position in a cool, ventilated space is generally kinder to it.

Why is my inverter showing a lower output than my panels' rating?

Almost always normal. Panels are rated under standard test conditions of 1000W per square metre at 25 degrees, which UK weather rarely delivers at the same time. Add conversion losses, cable losses, temperature derating and any deliberate DC to AC oversizing, and output below the panel rating is expected. A sustained drop against previous years is the thing to investigate.

Do inverters work in cloudy weather?

Yes, at reduced output, as long as the array clears the inverter's start-up voltage. Diffuse light on an overcast day still generates. Do solar panels work in cloudy weather has the detail.

What happens if my inverter fails out of warranty?

You replace it, and a modern replacement usually improves things: better efficiency, proper monitoring, and often the chance to go hybrid so a battery can follow. Panels, mounting and cabling all stay put, so it's a short job.

Does an inverter need servicing?

Not routinely, beyond keeping the vents clear of dust and cobwebs and checking the monitoring now and then. What it does need is somewhere cool to live. Heat is the single biggest factor in how long it survives.

Getting the inverter specification right

The inverter is where a solar quote quietly tells you how much thought went into the design. One MPPT on a split roof, a loft mounting position, no allowance for a future battery: all of those are cheap to do and expensive to live with.

CRG Direct has been designing and installing solar, battery and hybrid systems across the South and South East of England since 2017. We're MCS Certified and HIES Accredited, we handle the G98 or G99 application for you, and we'll specify the inverter around your roof rather than around the cheapest bill of materials.

Call 0330 133 2497 or email info@crgdirect.co.uk to book a free survey.