Micro Inverters And Ac Solar Panels: The Future Of Solar Power?

(Micro inverters are just one form of what's known as "PLO" - Panel Level Optimisation.

Initially, solar panels produced electricity in the form of Direct Current (DC) - the same type of electricity found in batteries.

To make this electricity usable for powering appliances or connecting to the grid, it needed to be converted to Alternating Current (AC) using a large box of electronics known as an inverter.

In grid-connected systems, solar panels were connected in series (known as strings) to generate higher voltage DC, which helps reduce losses. However, this approach also caused some issues.

That's where micro-inverters come into play.

Micro Inverters

A micro-inverter is essentially a miniaturized inverter designed to be compatible with individual solar panels rather than a string of panels.

While not a new concept - they first appeared in the late 1990s - micro-inverters experienced reliability issues and were quite expensive. However, in recent years, they have made a comeback and are gaining significant traction.

There are at least 21 different brands of micro-inverters worldwide, but Enphase is by far the most common brand (and the only one I'd recommend) in Australia.

Here's what one of these little fellas looks like compared to its conventional alternative, a big and powerful string inverter.

AC Solar Panels

An AC solar panel is essentially a solar panel equipped with a micro-inverter, allowing it to produce Alternating Current instead of Direct Current.

A typical "Series String" array

Currently, most solar panels installed in Australia are configured in this manner, with a single large inverter and a high DC voltage. If there's an arc at the 600V DC level, it could result in a bang! and potentially a fire (which is why you should never compromise on installation costs).

What's good about AC Panels and micro inverters?

There are a number of complexities caused by the traditional way of connecting solar panels together (in a series string) which Micro Inverters 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 micro inverters convert to 240V 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 thus cheaper.

Shading

To make this all a little more entertaining, I’ve put together a video discussing shading and solar panels. If you don’t particularly feel like watching, feel free to skip it and just read the summary below.

When solar panels are connected together in a series string, shading just one of them can dramatically affect the entire array (kind of like standing on a hose).

As an example: Here’s an array of 3 solar panels connected to a conventional, central inverter. One of the panels has been pooed on by a bird, which could easily reduce its output by 50%. However, it will also reduce every other panels’ output by the same amount: 

But by having a micro inverter on each solar panel, the outputs are completely independent of each other. So that bird poo is going to only affect the soiled panel:

According to the US National Renewable Energy Laboratory, this effect can yield as much as 12% more energy over a year. 

But – what has been the conventional thinking over years may need be revisited as string inverter technology has evolved. In a field test in 2021 that pitted a Fronius Gen 24 string inverter against En* microinverters, there was very little difference in how both handled varying degrees of shade across a single panel.

Whether this finding will turn out to apply across the board remains to be seen, but a report on a study of 200 solar systems in France published late in 2001 concluded there was no performance advantage to microinverters over string inverters generally.

Solar panel mismatch

When solar panels are manufactured, they may have slight variations in their electrical characteristics due to manufacturing tolerances. This results in a phenomenon called "mismatch" when you connect them in a series string. However, micro inverters can adapt to the individual characteristics of each panel, eliminating this mismatch.

Maximum Power Point Tracking

Different electrical characteristics of each panel also lead to different Maximum Power Points. The Maximum Power Point is the optimal point for extracting the maximum power from a solar panel, and micro inverters attached to individual panels can better target this point.

Monitoring and fault finding

While most inverters offer some level of monitoring and fault finding, they can only monitor the combined output of all panels in a series string. In contrast, micro inverters can monitor each panel individually, allowing for quicker and easier identification of issues.

Factory fitted

Some solar panel manufacturers now assemble micro inverters in the factory, creating AC Panels. This assembly in a controlled environment can save time and money.

Redundancy

If a series string inverter fails, the entire solar array stops producing power. However, if a micro inverter fails, the remaining units can continue to operate, resulting in a more reliable system.

Modularity

Series string inverters have limitations on the number of panels they can accept, making it challenging to add more panels later. In contrast, AC solar panels can be easily added because they are independent of each other, although adding a few panels to an existing array may come with additional costs.

Orientation

In a series string, all solar panels must be connected in the same orientation for proper voltage alignment. AC solar panels, on the other hand, can be oriented in any direction without affecting the operation of other panels.

Drawbacks of AC panels and micro inverters

However, AC panels and micro inverters also have some downsides:

Roof accessibility

In case of a micro inverter fault, someone needs to go on the roof to disconnect it from under the solar panel. This adds time and cost compared to removing a series string inverter from the wall.

Weather impacts

Being on the roof exposes micro inverters to more extreme weather conditions, including heat, cold, and moisture. This requires careful construction and the use of robust electronic components to ensure reliability.

Efficiency

While micro inverters are improving, they have not yet reached the same efficiency levels as series string inverters. This means they may not convert as much solar energy into electrical energy.

Price

Micro inverter systems typically add around 20-30% more to the cost of a solar power system compared to systems using conventional string inverters.

But BWN POWER microinverter can install easily in anywhere. There are no restrictions on the installation location, it can be placed in any corner, and it is not necessary to put it together with photovoltaic panels. Tentek micro-inverter can realize the home energy storage function, and the conversion efficiency is also close to that of traditional inverters.

When is an AC Solar Panel or Micro Inverter a better choice?

As you can see, there are a number of advantages to AC solar panels using micro inverters. The most common reason people choose them is because they have shading or they need to use different orientations on their roof to generate the power they require.

An increasing number of people are also choosing micro inverters because they are prepared to pay a premium to avoid mismatch, increase their redundancy and allow for future expansion. The other benefits described tend to strengthen the case and some people just love the idea of having the latest/newest technology.

Clearly, if you have shading or sub optimal orientation micro inverters are an ideal choice and could end up being cheaper in the long run because they will produce more energy.

Beyond this, micro inverters become a personal choice about how much you are prepared to pay balanced against the extra features and advantages.

Who sells AC solar panels and micro inverters?

There are numerous manufacturers worldwide that offer micro inverters. Additionally, an increasing number of distributors and dealers have access to micro inverters and can install them on various solar panels of your choice. However, if you're looking for a microinverter with storage function, only Enphase and BWN POWER currently provide such options.

The last word

Some readers have inquired about whether AC inverters can be a "Do-It-Yourself" (DIY) option, and the answer is no, although it's getting close. Since you're dealing with 240V AC power, it is still necessary to have a licensed electrician to handle the installation and, for rebates or feed-in tariffs (FITs), an accredited installer is required as well.

The market share of micro inverter-equipped AC solar panels is yet to be determined, but one thing is certain: they effectively address certain complex issues and have a promising future. If their cost can be further reduced, they may become the dominant solar inverter technology, rendering the big centralized inverters as obsolete as mainframe computers in the big electronic scrapyard in the sky.

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