Microinverters and AC Solar Panels: The Future of Solar Power?
By Finn Peacock, Chartered Electrical Engineer, Fact Checked By Ronald Brakels
Microinverters are just one form of what’s known as “MLPE” – Module Level Power Electronics (I prefer to call it ‘Panel Level Optimisation’). You can learn more about other types of MLPE here.
Micro Inverters
A micro-inverter is simply a miniaturised inverter, sized to suit individual solar panels rather than a whole roof of solar panels.
They aren’t new; they first appeared in the late 1990s, but arguably, it was a bit too early, and the technology suffered from reliability issues and high prices. In the last ten years, though, they have resurfaced and are starting to really take off.
Around the world, there are at least 21 different brands of microinverters, but in Australia, the most common brand by far (and the only one I’d use) is Enphase.
Here’s what one looks like next to its conventional alternative, a string inverter.
AC Solar Panels
An AC solar panel is simply a solar panel that has been fitted with a micro inverter (so that it produces Alternating Current instead of Direct Current).
A typical “Series String” array
Most of the solar panels installed in Australia right now are configured like this, with one big inverter and one big DC voltage. If that 600V DC arcs then there’s going to be a bang! And possibly a fire (which is why you should never skimp on installation cost).
A typical “AC Solar Panel or Micro Inverter” array
What’s good about AC Panels and micro inverters?
There are many complexities caused by the traditional way of connecting solar panels (in a series string), which microinverters can help overcome, including:
High Voltage DC
High Voltage DC produced by a series string solar power system can create a risk of very high-temperature arcing and potentially fire. Because microinverters convert to 230V AC, the potential for this to occur is greatly minimised.
Switchgear
High-voltage DC requires relatively expensive protective switches and fuses. By using AC, switchgear is more commonly available and a little cheaper.
Shading
Because microinverters optimise each panel separately, they handle individually shaded panels well and, for many years, were the obvious choice for solar arrays that had encroaching shade.
But – what has been the conventional thinking over the years is no longer true. The combination of split-cell solar panels and better ‘Maximum Power Point Tracking (MPPT) software in string inverters has made good string inverters almost as good as microinverters for handling shade.
In a 2021 field test that pitted a Fronius Gen 24 string inverter against Enphase microinverters, there was very little difference in how both handled varying degrees of shade across a single split-cell solar panel.
A report on a study of 200 solar systems in France published in late 2021 concluded there was no performance advantage to microinverters over string inverters generally.
Monitoring and fault-finding
Almost all inverters have some level of monitoring and fault finding however, it can only see the combined output from every solar panel in the series string. A micro inverter, however, can monitor each solar panel individually, allowing you to identify exactly what’s happening more quickly and easily.
Factory fitted
Assembling and connecting components in a factory environment is inevitably a more controlled environment and can potentially save time and money. Some solar panel manufacturers now factory assemble micro inverters to produce AC Panels.
Redundancy
If your series string inverter develops a fault, your entire solar array stops producing power until it is fixed. If a microinverter develops a fault, the remaining units can continue to operate, so you should have a more reliable system.
Modularity
Series string inverters can only accept a specific number of solar panels per inverter, so it’s not always possible to add a few more panels later. AC Solar Panels, however, can be added much more easily because they are independent of each other – though adding a handful of panels to an existing array won’t be cheap.
Orientation
In a series string on each string inverter input, all your solar panels need to be connected in the same orientation (or, in some cases 2, orientations) so they are combined to produce the right voltage at the same time to fire up that inverter input. Because they operate independently, solar panels with microinverters can be oriented in any direction and will not affect the operation of other solar panels.
What’s bad about AC panels and micro inverters?
They’re on the roof
If your micro inverter develops a fault, someone has to get up on the roof and disconnect it from under your solar panel. This can add time and cost compared to simply taking a series string inverter off the wall.
Weather effects
Because micro-inverters are on the roof (albeit under the solar panels), they suffer from more weather extremes including heat, cold and moisture. As a general rule, temperature extremes reduce the efficiency of electronic devices and shorten their life.
Efficiency
Although they are getting close, micro inverters have not yet reached the same efficiency levels as series string inverters, so they can’t convert as much solar energy into electrical energy.
Price
A microinverter system will add at leat 30% more to the cost of a solar power system compared to one using a conventional string inverter system.
When is an AC Solar Panel or Micro Inverter a better choice?
As you can see, there are several advantages to AC solar panels using micro-inverters. The most common reason people choose them is that they don’t want high DC voltages, they have shading or they need to install panels on more than 2 or 3 different roof directions.
An increasing number of people also choose micro inverters because they are prepared to pay a premium to monitor individual panels, increase their redundancy and allow for future expansion. The other benefits described tend to strengthen the case; some people love having the latest/newest technology.
Micro inverters are a good choice if you have severe shading or sub-optimal orientation.
Beyond this, micro inverters become a personal choice about how much you want to pay, balanced against their advantages.
Who sells AC solar panels and micro inverters?
The only ones I’ve ever seen in Australia are Enphase, Hoymiles and APS. Enphase is undoubtedly the market leader (and the only ones I’d put on my own house).
More Resources:
Can you add batteries to a microinverter-based solar power system? The answer is here.
A (slightly) cheaper alternative to microinverters are DC Optimisers
And finally, you can get 3 quotes for microinverter-based solar power systems here.