How micro inverters are solving problems

There is way more to micros than just dealing with difficult roofs or shading - they're lifting capacity and fattening up the daily production curve. But you've got to pick the right company.

In our previous post on micro inverters, we looked at how they have the potential to change business models. In this second installment we look at how they are solving real world problems for installers and consumers.

A crucial starting point is some Australian context. For a wide variety of reasons, Australia has a market that is almost exclusively driven by small scale residential sales. By the end of 2014, we predict that the national average rooftop penetration rate will be almost 30 per cent; an astounding and unique scenario in the world.

Obviously this varies by region, but one thing is unequivocally clear; those huge north facing roofs are less common than they used to be in the PV buying market place. We have been banging on about the probability of this for some time but recent events provided some evidence that this is now occurring with increasing frequency.

The first example I recently found was by scouring some of the online forums that talk about solar. A year ago, the talk was all about which installers and which products were best. The main thrust was about how to get a system installed as quickly as possible at the best price from a reputable supplier. But when I did a search recently, I found thread after thread talking about “difficult roofs”, “multiple orientations”, “the need to put PV on an upper and lower roof” and low and behold, a number of installers saying “the price difference between micro inverters and string inverters is not that much”.

Again and again the issue of tricky roofs came up and suddenly the light bulb went on for me; I’ll be damned if we aren’t now seeing a whole lot more difficult roofs starting to emerge. Anecdotally, perhaps the most interesting thing about rooftop penetration levels in Australia may be that once you pass around 25 per cent, you can pretty much count on that being the trigger for a different type of roof scenario and that makes for some really powerful business planning information.

The second example I can point to is even easier; open your eyes when you are driving through heavily solar populated suburbs. I’ve done this a lot lately and typically around 20 per cent of the systems I’m seeing are on split roofs are subject to partial shading. A random sample of eight systems I recently looked at (selected from 200 potential sites) had partial shading on 35 per cent of the roofs and multiple orientations on around 20 per cent.

The third example is a story published in Ecogeneration magazine recently. Their article “Smart solar is good news for retail outlet” highlighted how a shaded commercial site could only 18kW using string inverters but using micro inverters, the capacity was lifted to 29kW. That seems like a win for the shopping centre and a win for the installer if you are asking me.

So, the proportion of difficult roofs is increasing rapidly, I would suggest. It’s logical and backed by multiple sources of anecdotal and varied data sources. Micro inverters just make a world of good sense here of course, for all the reasons you know.

But there is way more to micros than just dealing with difficult roofs or shading.

Many installers were quick to point to publicly available data logging sites showing back-to-back data comparisons of micros and string inverters. Several sites showed similar performance benefits of around 5 per cent in unshaded, back-to-back tests. One installer has a great data set on the same roof, with the same orientation and pitch and was completely smitten with the results. Over a sample of 60 days of data, there was an average 7.7 per cent more energy delivered by the micro inverter based systems.

So micro inverters deliver more energy, even in unshaded sites? The data certainly seems to show that this is the case. The diagram below from the Enphase website shows why.

Graph for How micro inverters are solving problems

Solar arrays are not uniform and a whole lot of things can affect performance as we talked about in our last post. What I also learned from analysing the installer data and from their comments is that not only do these typically add up to more energy, but micro inverters also tend to start up earlier than string inverters, fattening up the daily production curve. They also generate more energy on low light days which is really helpful in the winter months when energy production is lowest, a point discussed at length on some of the forums and backed up by some of the data.

So, as Enphase highlight so well in their graphic, there is a whole lot more to micro inverters than just shaded sites.

The other interesting thing I observed in the forums was a little bit of history repeating itself. Just like the slow but inevitable realisation that all inverters aren’t created equally, the same discussion is now happening with micro inverters. There is a lot of debate and some good benefit of hindsight when it comes to choosing reliable, well supported products.

Like the flood of crappy inverters we saw in the rush, the number of micro inverters available has increased dramatically too. However, it seems that everything happens faster in the micro inverter world; industry is already very tuned in to the fact that cheap imitations are simply not going to last mounted on the roof, under a solar module. You really need to focus on companies who have big market share and are intensely focused on quality and service to get this right.

One major micro inverter supplier I spoke to was stunned at the recent growth in their sales of the top selling micro inverter brand in the world. “Last year we didn’t really offer the product and this year, I reckon the majority of our sales will all be that one brand. Installers have wised up very quickly."

Nigel Morris is the director of Solar Business Services.

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