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Are Microinverters Really Better than String Inverters?

By Aniket Bhor on in Solar Technology

Are Microinverters Really Better than String Inverters?

If you go to Google and type ‘string inverters vs. microinverters’, you will get dozens of articles telling you that microinverters are superior to string inverters.

In fact, we did almost the same in our last year’s microinverters vs. power optimisers article. But now we’re back again to tell you that, well, we were a bit wrong, and so were millions of people in the solar industry. Yes, we were a bit harsh on string inverters, and we are here to tell you the truth. So here we go!

Are Microinverters Seriously Better than String Inverters?

Before we begin the battle, here’s a quick recap:

  • Inverters are devices that convert DC power from solar panels into AC power, making it usable in our homes.
  • String inverters convert DC power from multiple solar panels (usually an entire string or array) into AC power at a single location.
  • Microinverters are small devices that convert DC power from each solar panel into AC power at the panel level.

Following are the existing, commonly accepted ideas about microinverters:

  1. Microinverters allow a higher power output
  2. They last longer
  3. They have better warranties
  4. They avoid system shutdowns
  5. They are safer

And to be fair, these aren’t entirely false, but the truth is - as it is in most cases - more complicated. These five facts aren’t as universal as everyone thought. Instead, they are true in certain specific cases.

So, if you were to choose between micros and stringies (bet you read that in an Aussie accent!), you would want to know which one would be better in your specific scenario, and that’s what we have come back to clarify. Let’s look at the above five arguments in more detail.

1. Microinverters allow a higher power output than string inverters

The idea that microinverters lead to better system performance is a blanket statement that leads us to believe that all microinverters are always better than all string inverters. This is clearly not true.

The belief that microinverters are better stems from the idea that systems with micros are more resistant to shading than systems with string inverters. Since each solar panel has its own microinverter, shading on one panel will not affect the entire string’s performance, as is believed to happen with string inverters.

Source: Fronius 

While this is true in certain cases, it may not apply to all systems in general. Modern string inverters, such as the Fronius Primo Gen24 Plus, have cutting-edge maximum power point trackers (MPPT) that keep an eye on production levels and prevent massive power drop even if just one panel is shaded.

Recently, a bunch of French scientists studied the performance of 100 systems with microinverters and 100 systems with string inverters. While the performance ratio (ratio of actual power generation to theoretical maximum) of both was expected to vary, both teams tied at a PR of 79%.

This was a surprising truth to face, almost like Galileo coming up and saying, ‘Bro, it’s the Earth that goes around the sun.’ But wait, let’s not jump to conclusions, it is important to know where these French gentlemen with difficult-sounding surnames gathered their data from. According to the paper, the installations in the study use Enphase’s older generation microinverters, and not a single system has the Enphase IQ series models - the latest and most reliable microinverters.

If we imagine a similar study conducted ten years from now, where most of the microinverters were the latest models, the PR for systems with microinverters would definitely be somewhat higher than that of inverter-based systems. But at the same time, we don’t think the difference would be too drastic - certainly not enough to become the sole reason to spend a few thousand dollars extra.

2. Microinverters last longer than string inverters

The lifespan of any solar equipment can make or break a deal. And the idea that microinverters last longer than string inverters is as widespread as the idea that they offer more power output. One argument that supports the longer lifespan theory is that microinverters don’t have any moving parts, and one of the most basic laws of engineering is that moving parts means friction means heat means degradation.

While string inverters use fans for cooling, microinverters such as the latest Enphase models use a special type of resin that is filled inside the casing to dissipate heat. However, there are two counter-arguments to this. Firstly, the fan in a string inverter is a very simple, small unit and is easy and cheap to replace. So, if it’s the fan that breaks down after 10 years of installation, it wouldn’t cost a fortune to fix it. Secondly, when a manufacturer tells you the expected lifespan of a device, you shouldn’t take them too seriously.

If someone is telling you that microinverters last 25 years and string inverters last just 10, tell them there are examples where string inverters have lasted up to 20 years. As for microinverters, the tech is so new that nobody has seen one actually last 25 years. Another reason people fret over the difference in lifespans is because of the difference in warranties, which is what we’ll talk about in the next section.

3. Microinverters have better warranties

A common argument in favour of microinverters is that they have longer warranties. This may be true in North America and Europe, where Enphase offers a 25-year warranty on its microinverters. But in New Zealand, we get a somewhat ordinary 10-year warranty.

Additionally, the supporting Enphase components don’t have stellar warranties either. For instance, the Enphase Envoy, which is a communication gateway, comes with a short, 5-year warranty; and Envoys breaking down because of lightning aren’t unheard of.

Now, these warranties are similar to the warranties of most major string inverter models. Yes, Fronius offers a measly 5-year warranty, but you can get another five years of extended warranty with certain installers, or if you’re willing to shell out a bit more money.

But if warranties are indicators of an equipment’s life, then the warranties of Fronius and most other reputable inverter brands paint a false picture. You may think that an SMA or Fronius inverter with 5-year warranty will last five years, but the beauty of these European beasts is that they can go on powering your home for 15 or 20 years without much trouble.

4. Microinverters avoid system shutdowns

One of the oldest stated advantages of micros is that if one unit fails, the remaining system still keeps working and there is no major loss in energy generation. While this is true, it is also important to note that repairing or replacing a microinverter can be a pain.

While string inverters are located in easy-to-reach spaces, micros attach to the back of solar panels. This means that a technician has to get to the roof and dismantle a panel to get to the faulty micro. Not a fun job!

5. Microinverters are safer

If one had to learn just one thing about electrical engineering, it should be this - DC power is much deadlier than AC power, especially at high voltages.

In a string inverter system, the DC power of an entire solar panel string or array is combined and sent to the inverter. This could be hundreds of volts, and if you accidentally burn or drill into such a DC cable, it would be extremely dangerous. Microinverters convert DC power from each solar panel into AC power, so there’s no high-voltage direct current anywhere in your system.
This makes the entire system safer.

While this is a very acceptable argument, modern string inverters are much safer than their grandparents. For instance, Fronius has something called the Arc Fault Circuit Interruption (AFCI), which reduces the risk of fire or shock from cables.

The Verdict

All the arguments presented above do not aim to label microinverters as pointless. The above points are true in many cases, and microinverters do make sense in these scenarios. However, you have to keep in mind the mantra stated previously - all microinverters are not always better than all string inverters.

Even in cases where microinverters would prove marginally better than string inverters, the added cost of a few thousand dollars may not make much sense.

So, to answer the question of ‘should you buy microinverters or string inverters’, we go back to our forever wise answer of ‘it depends’, because it really does. If shading is a serious issue on your roof, maybe the latest microinverters will prove better in the long run. If your roof is difficult to access, you’d probably want a nice reliable string inverter in a cozy, indoor spot of itself.

Ultimately, you have to decide if the extra money you’d spend on microinverters justifies the added benefit it offers - which will vary from system to system.

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