Looking to go solar, or upgrade an existing system? The inverter is the device that turns power from the solar panels into usable power for your home. It's usually the most complex part of a home's solar system, and often the first part to fail.
There are string inverters, microinverters, hybrids and power optimisers: each has pros and cons, so how do you sift through the quotes and claims and decide what's right for you? We'll guide you through the types and brands so you can ask your installer the right questions and get the best option to suit your home and budget.
The inverter is the box on the wall, or sometimes on the roof, that takes the direct current (DC) generated by the solar photovoltaic (PV) panels and converts it to alternating current (AC) for use in your household electricity circuits. It's usually the most sophisticated component of the solar PV system and unfortunately it's also the component most likely to fail first.
During a blackout
Most solar systems are designed to shut down during a blackout, but if you're willing to pay more, you can get an inverter that keeps your home's power running.
Regardless of the type, inverters should be Clean Energy Council (CEC) approved and should meet the Australian standard AS 4777. All the major brands are fine in these respects, but if your installer offers you a brand you've never heard of, ask for assurance that it's CEC approved.
What size inverter you need depends on the size of your solar panel array.
The size of the inverter is rated in kilowatts (kW) and is the maximum amount of solar-generated power that the inverter can manage.
How to calculate inverter size
- The inverter's maximum output capacity must be at least 75% of the solar array capacity.
- Or, expressed another way, the array capacity can be up to 133% of the inverter capacity.
This rule is laid down by the CEC, and solar PV systems must follow their rules to qualify for STCs (Small-scale Technology Certificates, the financial incentive scheme or "rebate" that applies to solar panel systems).
- String, hybrid and battery inverters should be mounted on a shaded wall, usually near the main switchboard. Inverters are designed to be installed outdoors and are usually weatherproof, but they don't like excessive heat; it can degrade their performance and lifespan.
- If your inverter can't be installed in a shaded area, your installer should suggest mounting an awning over it. Specialised awnings are available. In some cases a weatherproof housing might also be needed.
- Also consider security. String inverters can be a tempting target for a savvy thief if they are located in an easily accessible area. Theft is rare but not unknown. Installation behind a fence or locked gated area is best. Some models have anti-theft locking devices built in.
How much does an inverter cost?
- String inverters: The price of the inverter depends on its size and brand. You can pay from under $1000 to over $2000 for a string inverter.
- Microinverters: The cost depends to a large extent on the number of panels in the system and their rated output. One microinverter can cost around $200. The usual estimate is that a system with microinverters will cost about 20% more than an equivalent system with a string inverter.
- Optimisers: Similar but slightly lower costs than microinverters. However, adding optimisers to only a few panels that really need them could cost only a few hundred dollars.
- Hybrid inverters: These can cost in the $1000-$2000 range, but many models cost $3000 or more.
- Battery inverters: If a battery needs a separate battery inverter, this will typically add $2000-$3000 to the overall cost of the installation.
What about brand?
It's worth investing in a good name-brand inverter as it is a vital, hard-working component of the solar PV system. Enphase, Fronius and SMA are generally considered top brands and rate highly for satisfaction in our CHOICE member survey. There are other well-considered brands too.
- Your inverter should last at least five years – and will usually have paid for itself in that time – but ideally should last 10 years or more.
- Inverter warranties are typically five years, but look for warranties of 10+ years to cover the likely lifespan of the unit. For example, SolarEdge offers 12-year warranties and Fronius offers a five-year warranty with a free extra five years if you register the product online.
- Extended warranties are often available but you will usually pay extra. We don't usually recommend extended warranties for most products, but for peace of mind they may be worth considering in the case of your inverter, especially if you can negotiate one for low cost.
- Finn Peacock from SolarQuotes has looked into inverter manufacturer support for consumers who have a problem with their inverter but can't get help from the original installer, for example because the installer is no longer in business. The good news is that nearly all brands have stated that they'll assist consumers in these cases and will support direct warranty claims.
- Glen Morris from the Smart Energy Lab in Victoria points out that as long as your system (including the inverter) has already paid for itself, as it usually will after about five years or so, it's not necessarily a disaster if your inverter fails outside its warranty period. While it's certainly inconvenient to go without solar for a while, and to pay for a new inverter, you're likely to get a better, more sophisticated inverter for the money than you could a few years previously.
Once it's installed, familiarise yourself with your inverter. It will usually have a display and some indicator lights on it; get to know what these mean.
Whether you opt for smart software monitoring or just a visual check on the inverter's indicator panel, it's a good idea to periodically check in on your solar system. You'll spot any problems early, and it will help you shift your electricity consumption to make maximum use of your own solar power. You don't want to find out the hard way from an electricity bill that your system has been under-performing and you've been using grid power instead of solar!
Indicator panel and lights
- If the inverter has a display panel, this can show a range of data such as current power production, long term data and more.
- Indicator lights will typically show whether the system is running normally, whether there's a fault, whether the system is currently feeding power to the grid, and so on.
- Have a look at the display/indicators from time to time, say monthly, to make sure there are no errors or warnings needing attention.
- Many inverters and optimisers offer more sophisticated monitoring options. This is often done by a Wi-Fi or Bluetooth link to your home router. Your system's performance is logged and can be accessed via an app or a website. You can see how your system performs across the day and across seasons, track power fed into the grid and more.
- Note that if the inverter or optimiser brand goes out of business, the monitoring system might no longer be supported. Another good reason to go with major brands.
- If the inverter doesn't have a smart monitoring function, you could consider paying for a third-party monitoring system, such as Solar Analytics. These systems may involve ongoing fees for the service, but can deliver comprehensive reporting in return.
- Glen Morris agrees that monitoring is useful, but in his experience most people lose interest in doing this after the first few months. Don't pay for sophisticated monitoring if you aren't going to use it.
If your inverter is connected to the internet, make sure your home network is properly secured with encryption and passwords. Follow the inverter manufacturer's instructions for secure online connections.
Some key findings about inverters from our 2018 member survey on solar PV systems.
- CHOICE members reported buying many different inverter brands. The most common brands were SMA/Sunny Boy (28%) and Fronius (12%).
- The vast majority of respondents rated the performance of their panels, inverter and batteries positively.
- While we found very little difference in satisfaction between solar panel brands, satisfaction with inverter brands did differ, with Enphase, Fronius and SMA rating significantly higher than Sunny Boy and Aurora.
- Sunny Boy is a model name used by SMA, so they are in fact the same brand, but many respondents identified their inverter as a Sunny Boy while others identified theirs as SMA. Sunny Boy respondents tended to have systems of 2kW or less, which suggests they might tend to be older systems too.
- A whopping one-third of respondents (33%) have experienced problems with their system.
- The largest portion (20%) of those problems were with the inverter. Other issues reported were a decline in performance, problems due to a cable or connector, the panels themselves, and the framing or mounting structure.
- Half the people who've had a problem with their system have had the inverter replaced.
- 83% of inverter problems happened in the first five years (when they were likely to be under warranty).
- 98% of faulty inverters were replaced within the first nine years.
- Only 3% of Enphase inverter owners reported problems. This is significantly lower than owners of Aurora (17%), Fronius and SMA inverters (both 19%).
- Some respondents say they've had their inverter replaced multiple times.