The expert guide to solar panel inverters

Solar panel 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 solar inverters work as well as the factors to consider when choosing the right one.

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What is a solar panel inverter?

A solar panel inverter converts the direct current (DC) electricity generated by your solar panels into alternating current (AC), which is the type of electricity used by most properties. Without an inverter, you wouldn't actually be able to access your solar-generated electricity via your property’s wall outlets. 

Funnily enough, a lot of modern tech appliances like mobile phones actually use DC electricity to recharge, but they are set up to take AC electricity from a power socket and convert it into DC.

Why do you need an inverter for solar panels?

Your solar panel system will need an inverter for several reasons:

1. Conversion of electricity: Solar panels produce DC electricity, while your home’s power outlets need AC electricity. The inverter plays a vital role in converting DC electricity into AC electricity.
2. Optimising performance: Solar inverters also help monitor and optimise the performance of your solar panels. This ensures that you're making the most of the energy generated.
3. Grid connection: If your solar panel system is connected to the grid, you'll need an inverter to synchronise the electricity you produce with the grid's frequency. This is essential for selling any excess electricity to the grid.

There are different types of solar panel inverters, which we go into more detail about below.

How does a solar panel inverter work?

When solar panels receive light from the sun, they generate DC electricity. However, the grid uses AC electricity, as do the power outlets in the vast majority of properties. 

Because of this, the inverter must synchronise the DC electricity it receives with the electricity supplied by the utility grid. It does this by using a process called inversion, whereby the direct current is switched rapidly back and forth, creating an alternating current. 

This ensures that the solar-generated electricity can be seamlessly integrated with the grid and used to power your home. The inverter monitors the grid's frequency and voltage to match its output accordingly.

What are the two types of solar panel inverter?

The two main types of inverter are string inverters and microinverters.

Certified installers will be able to fit either kind – or both – with ease.

Let's go run through what sets the two types apart, and how you should choose the right one for your solar panels.

What is a string inverter?

A string inverter is typically the most common type of solar inverter used in homes. 

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

This type of inverter is usually mounted on a wall near your main electricity supply, providing a straightforward and cost-effective solution. 

However, one downside of a string inverter is that if one panel is underperforming, it affects the overall output of all the others connected to it.

To get around this issue – or if you have more than 12 solar panels in your system – your installer can fit more than one string inverter. Three is usually the maximum for residential properties, as this is typically enough for 36 panels.

What is a microinverter?

A microinverter is a smaller, more technologically advanced alternative to a string inverter. 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 performance. 

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

Which type of solar panel inverter should you choose?

When selecting a solar panel inverter, it is crucial to choose one that is best suited to your needs. Each type has its own unique features, benefits, and drawbacks.

String inverters are the most common and cost-effective solution. They are generally more affordable and easier to maintain than microinverters, making them a popular choice for many homeowners. However, as each solar panel is connected in a series (or "string"), if one panel underperforms the overall output will be affected.

Microinverters ensure that if one panel underperforms, the others are not affected. They are ideal for situations where shading, dust, or varying angles may impact individual panels' performance. They tend to be more expensive initially, but their long-term efficiency may be worth the extra cost.

How much do solar panel inverters cost?

What size inverter do you need?

What’s the minimum number of solar panels an inverter needs?

The minimum number of solar panels a string inverter needs is usually three or four.

A microinverter, on the other hand, has a minimum of one solar panel.

Some microinverters can handle more than one, but most are designed for a single panel.

What is an inverter’s MPPT?

MPPT stands for Maximum Power Point Tracker, and is a piece of kit that can be added to your inverter to optimise your solar panels' output to your solar battery or the grid.

When the sun is shining brightly and directly on your roof, your solar panels may generate DC electricity at too high a voltage for your battery. An MPPT can convert this output into electricity with a low enough voltage to charge your battery effectively.

This allows you to use more of the solar electricity your panels generate, instead of lots of it being lost and expelled from your panels as heat.

Most inverters have a maximum of three MPPTs, and often fewer. A certified installer will analyse your needs and make a recommendation that takes into account the various different factors involved.

If your inverter has the same number of MPPTs as it does strings, and your roof has an area that's more often shaded than the rest, your installer should put the set of more shaded panels on one string, with one MPPT.

The less shaded panels should then go on separate strings and MPPTs. Since the panels in each set will generate roughly the same as the other panels in their set, this will allow each MPPT to work efficiently, and maximise the solar electricity sent to your battery.

How efficient is a solar panel inverter?

A solar panel 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 model and an MPPT, which can both 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.

However, the ideal situation is generally a completely unshaded roof that uses string inverters, so it largely depends on your situation.

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.

Where should solar panel inverters be installed?

Solar panel inverters are typically installed somewhere inside or just outside your home, to minimise the length of the DC wiring, which reduces energy losses and the likelihood of electrical issues.

This generally makes a garage or cupboard under the stairs the ideal choice, as long as there's enough space to properly ventilate the heat from the inverter.

Otherwise, your installer may set up the inverter in a hallway, depending on the layout of your home.

Solar inverters are also usually designed to function outside. They can be mounted on a wall or dedicated structure, again preferably in a location that receives good ventilation and is well-shaded.

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

It’s also good to mount the inverter under an eave or weatherproof enclosure, to protect it from rain, hail, and snow. Choosing a location that is easily accessible for maintenance and monitoring is also wise.

Consulting with a professional solar installer can ensure that the installation meets safety standards and local regulations.

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

Do solar panel inverters make any noise?

An inverter will typically hum at a maximum of 30 decibels (dB), meaning it'll be, at most, as loud as a mostly silent library.

And the majority of the time, it'll reach the noise level of a whisper you hear from two metres away.

Some older models may be louder, but are unlikely to emit any noise over 45dB, which is roughly as noisy as a quiet household room.

And since your inverter will likely be in a cupboard or your garage, you'll almost certainly never hear it unless you're standing right next to it.

How long do solar panel inverters last?

The different types of solar inverters have varying lifespans. 

String inverters handle the electricity of an entire solar panel array and typically come with a 10-year or 12-year warranty. In most cases, a string inverter will need replacing at some point during the lifespan of a solar panel system.

Microinverters often have 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.

To ensure your solar inverter lasts as long as possible, periodic inspections and cleaning can limit the need for premature replacement.

Summary

Solar inverters are a crucial part of your solar panel set-up, converting the direct current generated by your solar panels into usable alternating current to power your home. There are several types of inverters, each with their own pros and cons, as well as varying price. It’s always a good idea to consult a solar professional who can advise on the best type of inverter for you.

If you'd like to know how much a solar & battery system could save you, just answer a few quick questions below, and we’ll calculate an estimate.

Solar panel inverters: FAQs