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Regarding micro inverters for solar power systems:

Is there technically a difference between an inverter classified as a "micro inverter" and and inverter classified as a "pure sine wave" inverter? Or is it simply a matter of using extra jargon to describe the size of the inverter?

Problem I'm trying to solve:

I'd like to purchase a micro inverter based solar system, where each panel has it's own dedicated inverter. Enphase seems to have coined the term "micro inverter" for this purpose, but the reseller doesn't offer a micro inverter that is big enough for a 315 watt panel.

So I'm wondering if I can purchase a pure sine wave inverter rated at 400 watts, for each 315 watt panel. Would those wire up the same way as the "micro inverter" solution?

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  • $\begingroup$ Why specifically do you want a micro-inverter system? Do you have reason to believe that you have very badly-matched PV panels? $\endgroup$
    – 410 gone
    Commented Nov 2, 2015 at 7:31

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"Micro" and "pure sine wave" are orthagonal, even if "micro" had a real definition. "Micro" is just a relatively content-free marketing term. It says that the inverter is intended for a small array or single panel, but of course without a spec it doesn't mean anything.

Anything connected back to the power line should be, and probably must be due to local laws, a sine wave inverter. "Pure" again is a silly marketing term. Surely the inverter will produce some harmonics. I guess the term is trying to say that the level of harmonics is low enough that the power company won't care. That's probably true, but you need to check that yourself since either you or the licensed electrician that installs it will be on the hook, not the sales guy who's telling you it's "pure".

So ignore micro, nano, or turbo, but make sure the output is within requirements in your jurisdiction. Otherwise, make sure the inverter will handle the volts, amps, and watts you will give it. If you have a 315 W panel, then a 350 or 400 W inverter sounds about right. A little more than the minimum is good in that it provides some margin. A lot more makes it too expensive, and it may not even run on a small power input. Too little is obviously bad. It either won't work or something will get fried.

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  • $\begingroup$ As an aside - feeding power back into the distribution grid should also require matching the phase of the power line. Otherwise, you're pushing reactive power onto the grid which doesn't really benefit anyone. That (obviously) wouldn't matter for a system disconnected from the distribution grid. $\endgroup$
    – user16
    Commented Nov 1, 2015 at 1:35
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Stop.

You can't just attach any inverter on a PV panel or array, even if it does have the right power rating.

Your inverter needs to be a PV inverter specificaly. It has to be designed to do max-power-point tracking. That's because the panel doesn't have any specific potential difference: that has to be imposed on it by the rest of the system.

Also, if you're connecting to the grid, the inverter may have to meet specific local regulations (e.g. G83 in Great Britain).

The whole idea of micro-inverters is that you have one per panel. And any micro inverter will be a sine-wave generator. The need for "purity" of that sine wave, and the ability to synchronise phases with the grid, as well as behaving properly upon grid disconnection, is what goes into things like G83 certification.

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