Solar inverters play a crucial role in any solar panel system, ensuring that the energy harvested from the sun is usable within your home.

As a core component of a solar installation, it's essential to understand how inverters work, as well as the factors to consider when choosing one.

In this guide, we’ll explain how an inverter works, how much they cost, which type you should get, and how often they need replacing.

To find out how much a solar & battery system could save you on your energy bills, enter a few details below and we'll provide an estimate.

How does a solar inverter work?

An inverter turns the DC electricity it receives from your solar panels into AC electricity that your home and the grid can use, in a process called inversion.

DC electricity only flows one way, so to convert it into two-way AC electricity, your inverter will use transistors to rapidly switch the direction of the DC electricity back and forth, until it turns into AC electricity.

It functions by connecting multiple solar panels together in a series, known as a 'string’. However, each model of inverter has a maximum number of panels it can incorporate on one string, ranging from around eight to 12.

However, one underperforming panel will affect the overall output of all the others on the same string.

When designing your system, a good installer should avoid shaded areas, or put the shaded panels on a separate string. This is the first port of call, before turning to optimisers or microinverters.

There's no maximum number of solar panels that a UK property is allowed to have, but you're unlikely to have more than three string inverters, as this would be enough for up to 36 panels.

Most domestic inverters no longer use a transformer to lower the electricity’s voltage so that it’s suitable to be exported, and instead rely on power electronics. 

As a result, they’re lighter, more efficient, and less prone to losses from magnetisation, copper resistance, and core hysteresis.

This all ensures your solar electricity can be seamlessly channelled into your home and the grid.

What is a hybrid solar inverter?

A hybrid inverter can act as both a solar inverter and battery inverter.

This means it can convert solar-generated DC electricity into AC electricity for your home and the grid, whether it’s coming directly from your solar panels or via your battery.

Before the creation of hybrid inverters, you’d need to pay for two inverters to perform these roles. Now, you can get one machine to do it all – and most people do.

Hybrid inverters are the industry standard for inverters, so in the vast majority of cases, the word ‘inverter’ refers to a hybrid inverter.

This can get confusing, especially when you see solar companies referring to ‘standard inverters’ and ‘hybrid inverters’, but as long as they can convert DC electricity coming from your panels and battery, they’re hybrid machines.

Hybrid models have become the norm thanks to the rise in popularity of batteries; around 94% of new solar panel installations in the UK include a battery, according to data from Flexi-Orb and EPVS.

How long do solar inverters last?

34% of inverters fail by the end of year 15, according to a Bern University of Applied Sciences study from 2023.

As a result, these machines – which handle the output of an entire solar panel array – typically come with a 10-year or 12-year warranty.

An inverter is therefore pretty likely to need replacing at some point during the lifespan of a solar panel system.

Microinverters often have longer warranties of up to 25 years, thanks to being less prone to heat damage and not having to handle the electricity of an entire array – but they’re relatively expensive (more on this further down).

Even if they don’t fail, an inverter’s efficiency will decline significantly as it ages.

The study’s researchers said that “inverters are still the most frequently failing components of PV systems”, and pointed out the high price of dealing with this.

They wrote that “the cost of maintaining and replacing inverters accounts for the largest share of the operating and maintenance costs of a PV system.”

This is one of the hidden costs of going solar that most installers won’t warn you about.

To ensure your solar inverter lasts as long as possible, you should arrange for periodic inspections and cleans.

Fortunately, every Sunsave Plus subscription is backed by the Sunsave Guarantee, which includes 24/7 monitoring and a free, out-of-warranty replacement inverter once it's required.

How much do solar inverters cost?

A string inverter for a solar panel system with 12 panels costs around £1,400.

This is just an estimate, though – the actual price you pay could be different.

It’s also worth accounting for the cost of a replacement inverter, which you’ll probably need at some point during the lifetime of your panels.

The good news is that the first time you buy a solar & battery system for your home, any inverters should come as part of the purchase and installation, so you won’t need to budget for it separately.

To learn more about the total price of going solar, check out our guide to solar panel costs.

And if you’re wondering how much a solar & battery system could save you on your energy bills, enter a few details below and we'll provide an estimate.

What size solar inverter do you need?

Your installer will tend to pick an inverter capacity that’s 80% to 90% of the system’s size. So if you have a 10kWp solar panel system, you’ll probably get an 8kW or 9kW inverter.

This should allow the inverter to run efficiently. A larger inverter receiving the same amount of electricity will be less efficient, which can cause it to suffer more wear and tear.

It's vital that your inverter's rating is lower than your system's rating, or it may not work some of the time.

Every inverter has a startup voltage – that is, the amount of power needed for it to turn on – but since panels don’t regularly hit their peak rating, the inverter is unlikely to overload, lose any electricity, or fail to start.

However, if you have a large amount of battery storage and want to use a time-of-use tariff to fill it all in five cheap, off-peak hours, your inverter will need to be big enough to handle this charging rate.

And if you have high-usage items that you want to run with solar electricity – such as an electric car or hot tub – you’ll again need a large enough inverter to handle this level of power.

But a good installer will take all of this into consideration and size your inverter accordingly.

The 3.68kW threshold

Once an inverter exceeds 3.68kW, the system will require permission from your DNO – that is, the company that runs the hardware supplying your area of the UK with electricity.

Your installer will send a G99 application to the DNO, and should handle the whole process.

This is necessary because it allows the DNO to prepare the grid for the electricity you’ll be exporting.

Any inverters below this 3.68kW threshold don’t require permission, so your installer should fit your system, then send a G98 form within 28 days of commissioning your installation.

Solar panel systems which need a G98 make up the majority of installations, and are sometimes known as ‘connect and notify’ systems.

Where should your solar inverter be installed?

Solar inverters should be installed one to two metres away from your battery.

They also need to be close enough to a router to connect to the wifi – unless they have an hardwired internet connection – and less than 50 metres from both your panels and consumer unit (also known as a fuse board).

If it’s any further from these devices, your system will endure a voltage drop, which means you’ll lose some electricity as it moves along the cables.

Your inverter and batteries should ideally be placed outside or in your garage, which your installer will know if they’re aware of the most recent guidelines, outlined in Publicly Available Specification (PAS) 63100.

Wherever your inverter and battery end up, the space should be properly ventilated and shaded to ensure neither machine overheats.

Direct exposure to sunlight can increase the operating temperature of the inverter, affecting its efficiency and potentially reducing its lifespan.

Choosing a location that is easily accessible for maintenance and monitoring is also a good idea.

To ensure your installation meets the latest safety regulations, it’s wise to hire one of the best solar installers in the UK.

To learn more, check out our guide to how solar panels are installed.

Are there any alternatives to string inverters?

There’s one main alternative to string inverters: microinverters.

A microinverter is a smaller, more technologically advanced device, made by the likes of Enphase and SolarEdge.

Each solar panel in your system will get its own microinverter, which allows for the individual conversion of DC to AC on a per-panel basis.

This can offer several benefits, such as improved system performance in situations where one malfunctioning panel would otherwise drag down overall system output. 

In addition, this setup enables easier monitoring and troubleshooting of problems, as issues can be identified at an individual panel level.

If you do use microinverters and have a solar battery, the AC electricity sent from your panels will need to be converted back into DC electricity to be stored in your battery. 

However, all modern top-tier storage batteries are more than capable of handling this additional conversion.

To learn more, check out our full guide to microinverters.

What about optimisers?

Optimisers aren’t technically a type of inverter, because they don’t convert DC electricity to AC electricity – but they do improve panel performance.

These small boxes connect to your panels and track their production with Maximum Power Point Tracking (MPPT), which is the same software that inverters use to maximise a system’s generation.

With this technology, they can take any shaded or otherwise underperforming panels out of ‘series’ and put them in ‘parallel’, so they don’t negatively impact the rest of the system.

However, they can’t replace your inverter, because they can’t convert electricity.

They’re also not as durable as microinverters, or as effective at dealing with shading.

Unfortunately, you’ll sometimes see optimisers incorrectly referred to as ‘power inverters’, which only adds to the confusion.

For more information, read our guide to optimisers.

What’s the best type of solar inverter?

String inverters are the most cost-effective type of solar inverter.

Microinverters are only your best choice if you have a significant level of unavoidable shade that would heavily reduce your energy bill savings, and which can’t be resolved in any other way.

And your installer should usually be able to find a solution in the design stage – such as by rearranging the panels, or by putting shaded panels on different inverter strings.

And it’s worth avoiding microinverters if you can, as they tend to make a system more expensive for no benefit.

A 2021 study by researchers at France’s Limoges University compared 200 standard domestic solar installations: 100 with microinverters, and 100 systems with string inverters – and found no significant difference.

The group wrote: “According to the production data, the performance ratio is ultimately almost identical for installations with inverters or microinverters.”

How efficient are solar inverters?

A string inverter is typically 93% to 98% efficient at turning DC electricity into AC electricity, though never 100%, as they need some DC electricity to function.

This is a reassuringly high efficiency level – though that range is still large enough that you should make sure you get a high-quality MPPT model, which can shift your system's output nearer to 98%.

Depending on how much shading there is on your roof, you may be able to boost your system's efficiency with microinverters, as they can maximise each panel’s output.

Microinverters themselves aren’t necessarily more efficient than string inverters, though – it varies from model to model.

Inverters are most efficient when working at their maximum capacity, so it's best if your solar panels can produce enough electricity to reach this point – but not too much more, as even with MPPTs you'll still lose some electricity to heat.

Next steps

Solar inverters are a crucial part of your solar panel system, converting the DC electricity generated by your solar panels into usable AC electricity to power your home and sell to the grid.

Microinverters are a potential alternative to string inverters, but should only be used in specific, rare circumstances. If you get a top-tier installer, they’ll be able to work out the best type of inverter for you.

To find out how much a solar & battery system could save you on your energy bills, enter a few details below and we'll provide an estimate.

Solar inverters: FAQs