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AC panels – smart panels are dumb May 5, 2013

Posted by Maury Markowitz in solar.
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Ever since microinverters and optimizers started hitting the market a few years ago, every one of these companies keeps talking about “AC panels”, also known as “module integration” or even “smart panels”.

The idea is that you put the inverter electronics right on the panel, so the installer doesn’t have to do two things at the construction site. Just install the panel, and AC power is coming out. Plug that into the breaker panel in the basement, presto, solar power system up and running.

This is a great idea, in theory. But non-standardization is dooming any possibility this will work. All of this would be trivial to fix, but I can’t find anyone in the industry that even sees the problem, let alone any reason to fix it.

So what exactly is the issue?

Standards are good

See that picture on the right? It’s one of the greatest things to ever happen to the solar power market. It’s called the MC4 connector.

MC4 connectors

Back in the distant past, 2007 say, panels didn’t have wires built into them. Instead, there was a little plastic box on the back, the “junction box” or “j-box”. To wire the panel up, you opened the j-box, and under the lid you found a couple of small metal screws. You passed your wiring in through some rubber grommets on the bottom of the j-box, stripped the ends off your wire, and then screwed the wire down to the “terminal block” using the screws.

Sound like a good idea?

No, of course not. For one thing, people can’t strip wire worth a damn without a good tool, and no one but an electrician buys the good tool. So most people ended up cutting off a bunch of the wire along with the insulation. And when you try to connect what wire is left, only some of it actually under the screw. And since the screw and the wire are almost always different materials, they rust, the wires tend to work their way loose over time, and water can leak in through the grommets. And, of course, people generally assemble these things during the day, when there’s power on the terminals – it is a solar panel after all.

So that’s why the MC4 is so great. Instead of you wiring the terminals the panel manufacturer does that for you. You get a sealed box with a pair of these snap-together connectors on the end. Now you can simply plug them together with any other panel that has MC4s, and you’ve got a waterproof connection that will last for decades.

And these days, all the panels use them. So if my Gizifa 240 panel ever dies on me, I know I can buy a Wizgigger 255 and it will plug right in.

Non-standards are bad

So here’s the main problem with the whole AC panel concept… none of the cables are the same. SMA uses something that looks like a large USB connector, Enphase has rectangular clamps that plug into these big plastic boxes permanently tied to the cable, Enecsys has round connectors that plug together in hubs, etc.

That’s nothing – the Enphase M190 doesn’t plug into the Enphase M380 doesn’t plug into the Enphase M215!

So imagine you buy a panel with an inverter built into it. Ok, so now if either the panel or inverter fails, you can’t replace it with any other panel. You have to buy a panel with the same inverter on it.

And you might not be able to, because maybe the manufacturer decided to change connectors on you. Or maybe the panel manufacturer got a better deal from someone else, and now they’re using a different model.

Have fun with that.

Talk, talk, talk

Wait, you say, it’s just electricity, all I need is some sort of adaptor plug. Sorry, not so fast.

The other thing your inverter is in charge of is monitoring what’s going on. This information is then collected in a hub box of some sort, and then sent out to the internet where you can pick it up on the web.

You know where this is going, right? None of the inverters can share their information with each other. In fact, they don’t even work the same way at all. Enphase and Sparq send information encoded in the power lines, Enecsys is wireless.

So not only are you going to find it difficult to plug them together, you won’t’ be able to see what’s going on.

So don’t buy one

So my advice is to stay as far away from AC panels as you can, at least until some of this stuff standardizes again. But the company’s involved don’t even consider this to be an issue, so that’s not happening any time soon.

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Comments»

1. Rusdy Simano - November 3, 2014

Regarding lack of standardisation with panels (hardware, comms, etc etc), my guess is we’re going back “the War of Currents” with these panels / inverters. I wish all our electrical appliances run on DC, so we can simplify much of these distributed energy sources. DC/DC converters are much cheaper too. Obviously, trying to change the momentum of AC appliances now is too difficult. (http://spectrum.ieee.org/green-tech/buildings/dc-microgrids-and-the-virtues-of-local-electricity)

Maury Markowitz - November 5, 2014

Neat article Rusdy, thanks for the link. I had never seen DC distribution before at this scale.


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