Power-One Aurora Micro mini-review September 19, 2013Posted by Maury Markowitz in solar.
Tags: micro-inverters, reviews, solar power
I had my first chance to try out the new Power-One Aurora Micro last week. It’s part a small twelve-panel install that we deliberately built with six PowerOnes and six Enphase M215′s. The system isn’t fully operational yet so I don’t have any production numbers to share, but that will definitely follow. Here’s some preliminary thoughts…
Update: both the P1 and Enphase have wireless networking now, so I’ve edited the article to reflect this.
In most ways the Micro and M215 are similar. Both are single-panel inverters, bucking the trend towards dual-panel boxes that SolarEdge and Tigo has been inching toward. Both systems use custom “trunk cables” to connect the inverters to each other. And both use wireline communications to send performance information to a data recording box, which lacks any sort of useful local interface. The biggest difference is the power ratings, the M215 puts out a maximum of 225 Watts, while the Micro is available in 250 and 300 Watt versions – the only difference between these two is the price.
Size and Weight
The most surprising difference between the Micro and the M215 is the size. There’s no way to describe this except through an image, which I’ve posted on the right. The larger size of the Micro is not an illusion, it really is about 50% larger than the M215.
I haven’t seen the Enphase M250 yet, but it’s basically the same size as the M215. So the much larger size of the Micro is not explained by its higher power rating.
Just as curious is the difference in weight – there doesn’t seem to be one. Whatever is taking up all that room in the box, it doesn’t weigh much. Film caps perhaps?
Cabling and installation
Also visible in the in the first image is the Micro truck cable – it’s zip-tied to the Kinetic Solar Main Rail on either side of the inverter. The connection point, or “drop”, is the translucent white object just to the right of the inverter. Actually that’s a cap that’s protecting the socket, you remove it to connect the inverter. The cable from the inverter is visible on the left side, although this image doesn’t show the actual connector itself (it’s under the inverter).
When the two are connected together the connector runs some distance out from the rail, so there is a degree of torque between the drop and the rail. However, the connector is relatively small and lightweight, so it doesn’t seem to be a problem.
You can see the corresponding Enphase Engage drop on the rail at the top of the frame – look for the bit of green. The connector, as you can see, is much larger. Likewise the connector on the inverter, located on the right side, is larger, heavier and “wider”. However, when the two are connected together the total distance from the rail to the cable is less, so the torque against the rail is lower and more spread out.
Another difference between the two is the gauge of the cable inside the trunk. Power-One uses 10-gauge wire, much larger than Enphase’s 12-gauge. This allows more power to be carried on the same run of cable, which can reduce the number of “strings” needed to build out the system. This can save money in some systems, especially if the Power-One system can be installed as a single string vs. the same Enphase system requiring two.
One problem with any trunk-based cabling system can be seen in this image… the longest distance of bare cable you can have is the distance from one drop to the next. Since the panels are about 100 cm (40 inches) wide, and you normally cut the cables between the trunks, that gives you about 50 cm of cable to work with at either end. This, quite simply, isn’t enough, the open end of the cable is somewhere near the edge of the panel.
One last note… trunk cables also have the disadvantage of having cut ends at both end of a string of panels. One of those ends has to be connected to the grid, so bare wire cut ends is what you want anyway. But the other end is another issue, this side isn’t connected to anything, so you have to cap it.
This brings up the only real problem I found when I was installing the system; the Power-One cap was extremely difficult to install and working with it resulted in a string of obscenities. The Enphase version went on without a hitch.
I touched on this earlier, but both Enphase and Power-One share the problem that they require an internet connection for any monitoring. Most companies offer local monitoring as the default, and internet as an option. Sparq’s box stores up to 20 years of data internally and allows you to get at it locally, which is great. SolarEdge builds it all into the inverters themselves, so you don’t even have to buy a box.
It gets worse. Power-One Micros do not turn on until they are connected to the internet! In this particular install, there is no internet in the building. So I’m going to have to buy a pair of WiFi bridges and use that to extend access to the building next door, just to turn on the system.
I cannot say this strongly enough: this is an brain-dead requirement that largely eliminates any possibility of using these devices outside urban or suburban residential systems. I couldn’t put it on my parent’s house, for instance, because they’re too far from the phone office to have ADSL.
I think the monitoring issue is a serious one, but to be honest it doesn’t effect the market this product is apparently aimed at, small residential systems. For these systems the Micro is priced right, and the longer strings might reduce overall installation costs compared to Enphase. Combine that with the higher power ratings and some larger panels and you can get more production out of the Micro than an otherwise identical Enphase setup. And combine that with the current $20 rebate and the system starts looking pretty attractive.