Has anyone tried two 12V PV panels in series with one Enphase microinverter?

Eugene

I'm testing two 100W "12V" 36 cell panels wired in series feeding one M215 microinverter, added to my existing 10-micro grid-tie rooftop system. This enables me to utilize remaining roof space that wouldn't accommodate full size panels. The specs for the current and voltages of the series-connected 12V panels fall well within the allowable specs for the M215.

I'm measuring instantaneous DC voltage and current from the panel pair at the point of the M215 DC inputs and I'm seeing voltage at about 33V under cloudy conditions and 31V under midday sunny conditions. Midday max DC power output is showing about 180W. On the AC side, the M215 hooked to these 100W panels is showing, via the Enlighten web interface, about 2/3 of the daily energy output as compared with an adjacent 260W full-size panel.

So, it appears the M215 is doing an adequate job of MPP tracking with the series panels. Has anyone else tried this, perhaps with other 12V panels of higher output (120 or 130W)?

Enphase would say that using the microinverter in this way would violate their warranty, but technically, as long as microinverter voltage/current limits are adhered to, why not do series PV input?

-Eugene (who wants to use ALL his available roof space)

Cariboocoot

Re: Has anyone tried two 12V PV panels in series with one Enphase microinverter?

Welcome to the forum Eugene.

There's really no difference between two "12 Volt" panels in series and one "24 Volt" panel. So long as the output specs are within range of the inverter. Therein lies one potential problem: cold Voc of the panels may be too high, as most of the "approved" panels for the M215 are GT style and run slightly lower Voltage. The specs say maximum input Voltage of 45, and it is possible for two panels with a a Voc of 22-ish to exceed this fairly easily. What will happen if it does I don't know. I do know that the warranty isn't valid if used with panels not on their list.

Usually if you have room for two 12 Volt panels you'd have room for one GT style. But I'm guess in you had a situation of "half the width, twice the height" to deal with.

Just beware that when the weather goes cold that one inverter might go "pfft!"

Eugene

Re: Has anyone tried two 12V PV panels in series with one Enphase microinverter?

Thanks for your reply, Caribo.

With the recent introduction of the M215IG (internal ground), Enphase upped the max Voc spec to 48V.

I am concerned, though, that if I need an inspection for my new grid-tie contract (new, because of the added capacity I'm adding over the original contract), that using non GT panels could be a problem. The Solarfennel Korean made 100W panels I'm using are listed as UL 1703 certified, but the AltE 100W and 120W panels I also want to use are not UL certified. Both Solarfennel and AltE are CSA and IEC61215 certified, however. Does it make a difference (UL or not)as far as the GT inspection goes?

Cariboocoot

Re: Has anyone tried two 12V PV panels in series with one Enphase microinverter?

They should only care about the UL listing, not the panel specifications.

What happens with your particular inspection depends on who does it and how much he understands.

BTW up here the 48 Volt spec wouldn't help much as the Voc could hit 57 in Winter.

BB.

Re: Has anyone tried two 12V PV panels in series with one Enphase microinverter?

In general, building inspectors, fire departments, and utilities have the right (and in theory, the obligation) to fail any electrical work done without UL Listed/Registered parts and appliances.

Some cities have that in their laws and enforce it without mercy (New York city was known for that--even to the point of inspecting/ red tagging coffee maker cords/pots).

Many do not:

Panel Fire Question

UL/NRTL Listings are, generally, a good indication that a company believes in their product enough to spend $50,000 +/- to approve and continue the factory inspection program.

Unlisted panels--No idea (sometimes they are the same panels, just sold as "B" grade panels with lesser/no warranties, remove UL label to avoid price pressure on "A" grade product, etc.).

And these days, some of the UL Labels are forgeries.

-Bill