[RE-wrenches] Micro vs (Modern) string inverter efficiency comparison

[August Goers]

Hi Dave -

We have a decent sized fleet of systems with both microinverters and string
inverters. For the microinverter systems, most of them are SunPower ACPV
with the micro built in at the factory. Annual production on these sites is
consistently 7% over PVWatts simulations and often hitting 15% or 20% over
our estimates year after year. Starting a few years ago, we started
introducing Tesla PV inverters with non-SunPower modules. Production on
these sites on average seems a bit lower, more like a couple percent higher
than what PVWatts simulations show. We've changed two variables - the
modules are not SunPower and we switched to string inverters, so it is hard
to pinpoint the exact causes of annual performance reduction. You might
find this Tesla whitepaper interesting regardless of whether you install
Tesla or not. There is a trend to add more MPPTs with lower input voltages
- this adds a lot of design flexibility to deal with shade, differing roof
orientations, module mismatch or uneven soiling, and even different module
types on one inverter.

https://digitalassets.tesla.com/tesla-contents/image/upload/Tesla_Solar_Inverter_Architecture_White_Paper_NA-EN_12212022

My current take on it is that micros probably do produce more per DC watt
on average, especially for heavily shaded roofs. Is the increased cost
worth it? That is the question. Long term system reliability is perhaps
more important of a factor.

August




On Mon, Nov 3, 2025 at 10:35 AM Dave Tedeyan via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi All,
>
> Does anyone have any real world data comparing the efficiency of
> microinverters vs. string inverters in a partial shading scenario? We all
> know the old selling point of micros with partial shading, saying that if
> one panel in a string is shaded,  you lose production from the whole
> string. But that is not the case anymore with at least SMA inverters with
> their global MPPT sweeps. If one panel is shaded, you lose the voltage from
> that one panel, and that is it, the rest of the string operates normally.
> In this case, it seems like micros don't actually add much value in a
> partially shaded system.
>
> I am thinking specifically of something like a fixed tilt ground mount
> that will be getting somewhere near 70% TSRF. So there are no issues about
> modules facing different directions. I am curious if there are actually any
> significant differences in power production with a microinverter vs a
> string inverter system in this case. Unfortunately, any article written
> about this subject assumes using an older string inverter where one panel
> being shaded will knock out the whole string, in which case the answer is
> pretty clear.
>
> Cheers,
> Dave
>
> --
>
> [image: Logo] <https://www.sungineersolar.com/>
> Dave Tedeyan, P.E.
> Owner | Sungineer Solar
> p: he | him | his
> a: 1653 Slaterville Rd. | Ithaca, NY 14850
> w: www.sungineersolar.com <http://www.sungineersolar.com/>
> c: (607) 270-0370
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