A solar inverter is the box that changes the direct current (DC) from your panels into alternating current (AC). Your home runs on AC, and so does the grid. Without an inverter, the power your roof makes would be of no use, because nothing in your home could run on it.

There are three main types. However, the choice affects cost, shade tolerance and upkeep. This guide explains each one, how to size it, and what to ask before you sign. For the basics of the whole system, see how solar panels work.

What an inverter does

The US Department of Energy explains the job well. A solar panel makes DC, and the grid uses AC. The inverter switches the DC back and forth very quickly to create a clean AC wave.

Modern units do more than that. They also monitor the system and talk to your home network. As a result, you can see your output in an app. Our later guide on reading your solar monitoring app shows what the numbers mean.

Inverters also protect the grid. The Department of Energy says a household inverter should ride through small dips in voltage or frequency. However, if the problem is large or lasts a long time, it disconnects and shuts down. That is why a plain solar system goes quiet in a power cut.

The three main types

String inverters

A string inverter connects a group of panels, called a string, to one box. The Department of Energy calls this set-up cost-effective.

The weak point is shade. If one panel is shaded or damaged, output falls across the whole string. Therefore, string inverters suit simple, unshaded roofs best. Our guide to how many solar panels you need explains how roof layout feeds into the design.

Microinverters

A microinverter is a small unit fitted to each panel. The Department of Energy says shading or damage to one panel will not affect the power drawn from the others. However, microinverters can cost more.

They can suit roofs with patchy shade, so ask your installer if that applies to you. Although they work well, there are more parts on the roof, so ask about the warranty on each one.

Hybrid inverters

A hybrid inverter handles panels and a battery in one box. The Department of Energy notes that solar can charge a battery directly over DC, or after conversion to AC. Both routes exist.

A hybrid unit can suit you if you want a battery now or soon. While it costs more up front, it may save a second inverter later. If you only might add one later, ask about a battery-ready design. Our guide on solar battery cost and sizing covers the storage side.

Choosing the right size

Inverter size is rated in kilowatts (kW) of AC output. Panel size is rated in kilowatts peak (kWp). The two do not need to match exactly. Still, they should be close.

Your grid connection sets a ceiling. National Grid says a small system under 16 amps per phase can use the G98 route, and the installer notifies the network within 28 days of commissioning. On a single-phase supply, that is about 3.68 kW. Bigger systems need approval first under G99, which our post on DNO grid connection, G98 and G99 explains.

Ask about the panel-to-inverter ratio

Some designs pair a larger panel array with a smaller inverter. For example, a 4 kWp array might sit behind a 3.68 kW inverter. This can be fine, but ask the installer to explain any expected loss at peak times. Compare that with the estimate on your quote.

Warranty and replacement

The inverter and the panels carry separate warranties, and their lengths can differ. Always check both in writing.

Home Energy Scotland says solar panels should last 30 years or more, and MCS says they can last over 20 years. Energy Saving Trust says an inverter usually needs replacing after around 12 years, and its maintenance guide gives 10 to 15 years at a cost of around £800. Warranty terms are set by the maker, so check them. Ask for the warranty length, who pays for labour, and what happens if the maker closes. Our piece on solar panel lifespan and degradation looks at the long view.

Check the cost of a replacement too. Add a possible swap into your long-term sums when you ask are solar panels worth it. Our guide to cleaning and maintaining solar panels covers what you can check yourself, while our hub on solar panel maintenance and lifespan gathers the rest.

Registering your inverter

Your network operator needs to know about your system. GOV.UK guidance says you must register an energy device in your home with your Distribution Network Operator (DNO). The DNO is the company that brings electricity to your property.

Your installer normally handles this for you. However, ask to see the paperwork before you pay the final invoice. Keep the commissioning certificate and the inverter manual somewhere safe, because you will need them if you sell the house.

Power cuts and backup

Many people expect solar to keep the lights on in a power cut. In most cases it does not, since the inverter has to switch off for safety. A standard inverter shuts down when the grid fails, as described above.

The Department of Energy says solar-plus-battery systems can run without grid support in an outage, but only if they are designed to. So if backup matters to you, say so at the quote stage. Expect a different design and a higher price.

Winter and shade

Inverters do not change the sunlight, yet they shape how well you cope with weak light. Shade is the big issue, because output on a string drops with the weakest panel. Our post on solar panels in winter shows how low winter light cuts output, and why shade matters more then.

Questions to ask your installer

Since quotes differ so much, take this list to each one.

  • Which inverter type is proposed, and why does it suit my roof?
  • What is the model, its AC rating and its warranty length?
  • Is it ready for a battery, and what would that cost?
  • Does it connect under G98 or G99?
  • Where will it be mounted, and can I see the display or app?
  • Is the installer MCS certified? Our hub on choosing an installer explains why that matters.

Our hub on batteries and export helps if storage is on your list. Get at least three quotes and compare them like for like.

Sources

Common questions

What does a solar inverter do?

It changes the direct current (DC) from your panels into alternating current (AC). Your home and the grid use AC. Most inverters also track output and send data to an app.

What is the difference between a string inverter and a microinverter?

A string inverter serves a group of panels. A microinverter sits on each panel. With microinverters, shade on one panel does not drag down the others.

Do I need a hybrid inverter for a battery?

Not always. A battery can use its own inverter, or share a hybrid unit with the panels. Ask your installer which route they plan and why.

Will my solar panels work in a power cut?

Usually not. Grid-tied inverters switch off when the grid fails. A battery system only keeps your home running if it is designed to do so.

How big should my inverter be?

It should suit your panel total and your grid connection. On a single-phase home, an inverter under 16 amps (about 3.68 kW) can use the simple G98 route.