What is a micro-inverter?
A micro-inverter is device that connects to a single solar panel, converting DC (direct current) from the panel into AC (alternating current), which can power household appliances or be sent into the grid for energy credits. Unlike string inverters, micro-inverters control the output of a single panel. This article outlines the pros and cons of using micro-inverters in your solar power system.
In solar power systems, the inverter is like the brain of the system. It takes the DC (direct current) electricity produced by solar panels and converts it into AC (alternating current), a format that can be used to power your appliances and sent into the utility grid.
Traditional inverters, called string inverters, are designed to manage groups (or series strings) of panels plugged into an input on the inverter. For example, you might wire 24 solar panels into an SMA Sunny Boy inverter in two strings.
But micro-inverters are different. In a micro-inverter system, each micro-inverter is paired to its own panel. So in the same 24-panel system, you would have 24 micro-inverters installed—one on each panel.
On a per-panel basis, micro-inverters like the Enphase IQ7+ cost a bit more than basic string inverters. But micro-inverters come with features that can optimize the overall output of your system, providing a boost in efficiency that offsets the higher up-front cost.
In this article, we’ll explain what a micro-inverter is, then outline the pros and cons of micro-inverters to help you decide whether you should consider them for your solar project.
What is a micro-inverter?
In simple terms, a micro-inverter is an inverter that controls the output of a single solar panel. Each micro-inverter that is paired with a solar panel essentially creates a self-contained solar energy system.
Mount it to the back of the panel, plug it in, and you’ve got a system that produces energy, regardless of whether you’ve installed 1 panel or 100.
Advantages of Micro-Inverters
Due to the way they’re configured, micro-inverters have a few key advantages compared to string inverters that justify the higher price tag.
In order to explain the problem micro-inverters are built to solve, we first need a bit of background context about how string inverters work.
With a traditional string inverter, groups of panels are wired in series. If you have 8 panels in a string, all 8 panels are part of the same circuit, which means they are subject to the same electrical characteristics.
If the output of a single panel drops, the whole circuit drops to match the reduced output of the under-performing panel. You might have a string of 350W panels, but if one panel falls to 300W output, every panel in the string is restricted to that 300W mark.
With micro-inverters, each panel is isolated from the rest of the array. One shaded panel may drop to 300W, but the rest of the panels remain unaffected and continue to produce at its 350W capacity.
The net result is that micro-inverters allow you to produce more power out of the same panels. In areas where trees or other obstructions will cast shade on your panels, micro-inverters are well worth the investment.
Isolated Equipment Failure
Similar to the above point, if a piece of equipment fails completely, the rest of the array won’t be affected.
Let’s say a panel malfunctions due to faulty wiring and stops producing power. With micro-inverters, that panel is isolated, so the rest of the array keeps producing power. The other panels will continue to work, so you are not stuck without a working system while you file a warranty claim and get it replaced.
With a traditional string inverter like the SMA Sunny Boy, the entire string could be affected to the point where the inverter wouldn’t produce power. You could potentially be left in the dark until you replace the faulty panel.
Ease of Installation
Micro-inverters use standard AC wiring, similar to what is used throughout your house. They are also plug-and-play, with each unit plugging into the next.
As a result, micro-inverters are extremely easy to install and connect because they use standard AC wiring and it only takes a few seconds to plug in each unit.
What if you want to start small and expand your system later? Maybe you don’t have the budget to offset 100% of your energy usage, but you want to get into a smaller system so you can start reaping the benefits of solar. Or maybe you want a self-contained array to power your shed as a “test run” to see if it makes sense to power the rest of your home with solar.
Due to their 1-to-1 nature, systems with micro-inverters can essentially be as small or as large as you want them. If you want, you can start with a single panel+micro-inverter pairing. Adding more panels later isn’t a problem, because none of the existing equipment needs to be moved or re-wired to facilitate the addition.
The same isn’t possible with string inverters, which have minimum string size requirements because the panels need to supply enough voltage to the inverter to power it on. In the linked example, the system is limited to 7-10 panels per string. Outside that range, the inverter may not function properly.
Which means that if you have any future plans for expansion, micro-inverters are the way to go. You can start with a small system now and add on to it later without hassle.
Flexible Array Layout
Panels produce the most energy when they face South (directly at the sun), while East- and West-facing panels will lag behind.
With string inverters, you typically want all panels in a string to face the same direction. If you mix South- and East-facing panels on the same string, the panels facing East will drag the rest of the string down.
Micro-inverters give you more flexibility with the layout of your array. Depending on your roof configuration, you may need to design a system to distribute panels across multiple sections of your roof. With micro-inverters, the output of each panel is isolated, so you can distribute them however you want without sacrificing output.
Meets Module-Level Rapid Shutdown Requirements
Lastly, the IQ7+ is designed to meet Rapid Shutdown requirements outlined in the latest version of the National Electric Code without the need for any additional equipment.
In short, solar systems need to be able to “de-energize” quickly in case of emergency. If a house were to catch fire, the firefighters may need to climb on the roof and cut a hole to ventilate the smoke. In doing so, they could cut through the solar wiring, which is often routed into the attic to run alongside the roof rafters.
As a safety measure, roof-mounted systems need a way to quickly release the live current running through the wires, to prevent the risk of shock for first responders.
The IQ7+ meets Rapid Shutdown requirements by default. For the SMA Sunny Boy, you’d have to add something like the FireRaptor Rapid Shutdown Unit at an additional cost to meet the regulations.
It’s worth noting that this section only applies to roof-mount systems. Ground-mounted systems won’t interfere with first responders who need to work on your roof, so they’re exempt from the Rapid Shutdown requirements.
Disadvantages of Micro-Inverters
More Expensive Up Front
Of course, the flexibility and added features of micro-inverters make them more expensive than traditional string inverters. A system with Enphase IQ7+s will cost around 15-20% more per panel than an equivalent SMA Sunny Boy system.
That higher initial investment is well worth it if you live in harsh climates, where inclement weather can put a damper on production. It also makes sense if your site is shaded by trees or other obstructions. In these cases, micro-inverters will salvage production that would have otherwise been lost, easily offsetting their higher price tag.
But if your system will be built in a location with full sun exposure, a standard string inverter is a perfectly good option. If shading isn’t a concern, the SMA Sunny Boy will perform comparably to a micro-inverter system at a much lower price point.
Higher Odds of Equipment Failure
In the “pros” section, we mentioned that adding a micro-inverter to each panel can isolate equipment failures. Even if a panel malfunctions, the output from the rest of the array won’t be affected.
The flip side is that micro-inverters introduce more potential failure points. If your system has 24 micro-inverters, the odds that a piece of equipment will malfunction go up compared to a system with a single string inverter.
Another point is that micro-inverters may be more challenging to replace for rooftop installations. Since they are attached to your panels, it may be a pain to climb on the roof and replace one in the middle of an array. By comparison, string inverters are always installed at ground level, making them much easier to replace if necessary.
When Are Micro-Inverters the Right Choice?
Micro-inverters are the best option if you need to build your system under less-than-ideal circumstances. If your panels will be shaded, or part of the array will face East/West due to the configuration of your roof, micro-inverters ensure your system produces as much power as possible.
If you have plenty of space to build your array in full exposure to sunlight, a traditional string inverter may be the better bet, as it can perform the same job for 15-20% less money up front.
For more info, check out our reviews of a few inverters we carry:
You can also grab a free copy of our Solar Inverter Guide by clicking below.