What kind of inverter is more reliable? A transformer based one or Non Transformer one??

RCinFLA

Re: What kind of inverter is more reliable? A transformer based one or Non Transformer o

boB wrote: »

Transformer-less or "ungrounded" grid tie inverters are becoming pretty popular in the US after EU started doing this...

Here is one link that talks about it.
http://www.solarworld-usa.com/system-designers/~/media/Global/PDFs/Grounded-vs-Ungrounded.pdf



There is a list of ungrounded (transformer-less or non-isolated) inverter companies here...

https://homepower.com/articles/ungrounded-pv-systems/page/0/2


I don't think I would want to use a non-isolated battery based inverter, myself.

boB

The inside photo of the SMA inverter show a rather large bank of electrolytic caps to provide the single phase cosine^2 power pulse filtering. I am not a fan of using electrolytics for this application even when it is a central unit mounted in a location not exposed to high temperatures. Oil filled non-polarized caps, although larger in size and cost, are more reliable.

There was a big stink about the large bank of electrolytic caps in the early Enphase, per panel, GTI's. They and other manufactures have since change out to non-polarized mylar caps on the high voltage DC boost. The additional issue in the per-panel GTI's is the greater likehood to be exposed to high temps further stressing the electrolytic caps.

PV panels need a relatively constant current loading to maintain maximum power point voltage control. Doing this with caps at the panel terminals requires much larger capacitance to hold down the 120 Hz ripple current seen by the panels. The more 120 Hz ripple current seen by the panel, the less power the panel produces. It is much easier to boost the panel voltage to the high voltage DC which can allow more ripple voltage at this point that is compensated out by the PWM sinewave converter. The more the allowable ripple voltage at this high voltage DC, the less filter cap size required. The issue is electrolytic caps life span is reduced the greater the ripple voltage it sees.

The second issue for transformerless is the narrow stack voltage range required. Although it is true that a transformer will have about a 1%-2% loss there can be more net loss in a transformerless design due to more time where there is insufficient minimum panel voltage. Just a small amount of shading on one panel can shut down the grid power push. It may also shut down if the panels get too hot, droppng the Vmp point.

boB

Re: What kind of inverter is more reliable? A transformer based one or Non Transformer o

More energy stored at higher voltage is certainly true. That can be done with a transformerless or transformer inverter.
Non isolated inverters still use inductors.

AFAIK, the non-isolated transformerless inverter has a couple % better hardware efficiency than the transformer ones.

There was an instance many years ago where a nonisolated inverter was used and they were made to add a transformer
between inverter and grid which ate up any efficiency increases they would have had. Can't remember which one
it was but I remember that the inverter was larger than just a few kW.

boB