Solar inverters

Panels get most of the attention, but the inverter is arguably the most important component of a solar system. It converts the panels' DC power into AC for your home, squeezes the most energy out of the panels as conditions change, keeps the system safe, enforces export limits and records generation. It's also the component most likely to need replacing during a system's life.

This guide explains the main types of inverter, how they compare, what the specifications mean and what to consider when choosing one.

What an inverter does

The inverter's main job is converting DC electricity from the panels into AC at the voltage and frequency of the grid. It also:

• Tracks the maximum power point of the panels, constantly adjusting to get the most power as light and temperature change.
• Monitors the grid and disconnects if the grid fails, as required by Australian Standards.
• Responds to voltage and frequency changes according to grid settings for your region.
• Limits exports if your distributor requires it.
• Records generation and reports faults, usually through an app.

String inverters

A string inverter is a single unit, usually mounted on a wall near the switchboard, connected to one or more strings of panels wired in series. String inverters are the most common type in Australian homes and generally the least expensive per kilowatt.

Their main limitation is that panels in a string are linked, so shade or a fault on one panel can reduce output from the whole string. Inverters with two or more maximum power point trackers (MPPTs) can manage separate strings independently, which helps when panels face different directions. String inverters suit simple, unshaded roofs well.

Microinverters

Microinverters are small inverters fitted behind each panel, converting DC to AC right at the panel. Each panel works independently, so shade or a fault on one panel doesn't affect the others. Microinverters suit roofs with partial shade, several roof faces or space for only a few panels on each face. They also provide panel-level monitoring and avoid high-voltage DC cabling running across the roof.

Microinverter systems typically cost more than string systems, and because the units sit on the roof, replacing one means a roof visit.

Power optimisers

Power optimisers are small devices fitted behind each panel that work with a central string inverter. They optimise the output of each panel individually, reducing the effect of shade and mismatch, and usually provide panel-level monitoring. Systems with optimisers sit between string inverters and microinverters in cost and complexity.

Hybrid inverters

A hybrid inverter manages both solar panels and a battery. It can charge the battery directly from the panels and supply the home from either source. Some hybrid inverters provide backup power during a blackout. If you plan to add a battery soon, a hybrid inverter may save you replacing the inverter later, although batteries can also be added to an existing system with an AC-coupled battery. Read our battery guide.

Comparing inverter types

• Simple, unshaded roof, one or two faces: a quality string inverter is usually the most cost-effective choice.
• Partial shade or many roof faces: microinverters or optimisers can recover energy lost to shade and mismatch.
• Battery now or soon: consider a hybrid inverter, or plan for an AC-coupled battery.
• Want panel-level monitoring: microinverters or optimisers provide it.

Sizing the inverter

An inverter's size is its rated AC output in kilowatts. Installers often pair an inverter with somewhat more panel capacity than its rating, because panels rarely produce their full rating in real conditions. This increases generation in the mornings, afternoons and winter, with only small losses at peak times when output is limited by the inverter. Scheme rules and the manufacturer's specifications set limits on how much extra panel capacity can be connected. Your distributor may also limit inverter size, particularly for single-phase homes.

Understanding inverter specifications

• Rated AC output (kW): the maximum continuous power the inverter delivers.
• Maximum DC input: the maximum panel capacity and voltage the inverter can accept.
• Number of MPPTs: how many independent groups of panels it can manage.
• Efficiency (%): how much of the DC power is converted to AC. Peak and weighted efficiency figures are both quoted.
• Phase: single-phase or three-phase, to match your supply.
• Communications: Wi-Fi, ethernet or other connections for monitoring and remote settings.
• Warranty: length and terms, including whether extensions are available.

Where the inverter goes

Inverters generate heat and are sensitive to high temperatures. Install them in a shaded, well-ventilated location, protected from direct sun and rain, such as a garage wall or a sheltered outside wall, following the manufacturer's instructions. An inverter baking in afternoon sun may reduce its output to protect itself and age faster. Inverters also make a gentle hum, so avoid placing them on a bedroom wall.

Monitoring and connectivity

Most inverters include monitoring through an app or website. Keep the inverter connected to your home internet so monitoring works and so the inverter can receive updates and, where required, remote settings. Consumption monitoring, which measures your household's usage as well as generation, usually requires an additional meter or current sensor and is well worth having.

Grid support and remote settings

Inverters must be set to the grid settings required in your region, which govern how they respond to voltage and frequency changes. In some states, new systems must be capable of remote management in rare grid emergencies, and some distributors offer flexible export limits that require internet-connected inverters. Check that the inverter you're quoted supports the requirements in your area.

Warranties and replacement

Inverters typically have shorter warranties and lifespans than panels. Check the warranty length, whether an extended warranty is offered, who backs the warranty in Australia and how claims are handled. When an inverter eventually fails, replacing it is usually straightforward, though a new inverter must meet current standards and settings, and may need network approval if its size changes.

Signs of an inverter problem

• Your monitoring app shows no or low generation on a sunny day.
• The inverter display shows an error or fault light.
• The inverter is unusually hot, noisy or smells of burning.

If you notice any of these, check your app and inverter display, then contact your installer. Don't open the inverter or attempt electrical repairs yourself; it contains dangerous voltages even when the grid is off.

Inverter noise and appearance

Inverters make a gentle hum and some have cooling fans. Choose a location away from bedrooms and quiet outdoor areas.

Questions to ask about inverters

Ask which inverter type the installer recommends and why, whether it supports a future battery, how many MPPTs it has, where it will be mounted and who handles warranty claims.

Key points

String inverters suit simple, unshaded roofs and are the most common choice. Microinverters and optimisers handle shade and complex roofs and give panel-level monitoring. Hybrid inverters manage panels and batteries. Choose an inverter that suits your roof and plans, install it in a shaded, ventilated spot, keep it online and check its warranty.