Thanks for the cross link BB .. content is welcome!

As for the Xantrex GT ... one just moves the GFI fuse .. thats it. The Xantrex GT is transformer isolated and doesn't care which input is at ground potental, never tried it, but that what I have been lead to beleive.

that's a good example of where i'm going bill as you bring up the incompatability of many negatively grounded items that can't go into a positively grounded car. apply now to solar equipment?
ok sg we similtaneously posted. ok on xantrex being able to go either + or - grounding. any other nonxantrex stuff that you are aware of that might fill that catagory of being able to go both ways? it is somewhat of a curiousity question as sunpower is the only one needed this.
hmmm. i bet they had some troubles with the nec too.

At least 20 years ago when I was designing DC powered Voice Mail Systems for the telephone companies--I would not go by what was in the NEC of that period as to the best methods for designing DC based power systems. Last I saw a while ago, it was better--but from the discussion on Wind-Sun it was apparent that the NEC was getting into design guidelines that had little to do with safety--generally not (IMHO) where they should position themselves (types of grounding for RFI and negative vs positive grounding is an example).

The Telephone Companies' Lab (Bellcore, Telcordia, or whatever it is called now) had much more experience with designing dedicated, long lasting, reliable and safe practices. But their design requirement books were horrendously expensive at the time.

Again, in my opinion, NEC should not cause SunPower one bit of grief over +/- grounding. It is NEC assuming that negative ground is "standard" that is causing issues--I am old enough to have worked on other cars (European, an old Kaiser, etc.) that had positive ground systems to know not to assume anything of the kind.

In one of the other Wind-Sun posts, there were "complaints/observations" (by NEC or others working with the NEC) about the problem with ground loops caused by DC grounded chassis (because of the way cars and their equipment assumes metal chassis is DC ground). Ground loops in a car are not a problem--it is just a "cheap" wire. Ground loops in other things (like ships) can be a problem because they can cause corrosion and if the current passes through bearings/joints--they can weld bearings/hinges and cause failures (i.e., hinges on aircraft control surfaces have metal braided wire jumpers across hinges/bearings).

The need appears to be the the result of placing the current contacts on the back of the cell--this can increase solar efficiency (because no contacts to block sun), but leaves the "top" of the solar cell without any metal contacts to bleed off / equalize the "positive holes" left behind when photons travel through the silicon to generate current.

If SunPower were to change back to front contacts or add another process step to place a (clear?) conductive layer on the top surface--this issue would go away (and it appears to be significant--a 200 watt panel will derate down to 140 watts after a few hours of sun if held at a +160 potential wrt ground). Connecting to positive ground will "fix" any problems and prevents it from ever happening again.

But since they appear to be focusing on large (i.e., Grid Tied) installations where the polarity of the ground is a "don't care" for the inverter manufacturers--there is probably no reason to add extra steps (and costs) to their products at this time.

I have not taken apart a MPPT charge controller, but they can probably be designed (if not already designed that way today) with isolation very easily if grounding were to become a big issue.

-Bill

xantrex appears to be one that takes into account being able to positive ground and i was just curious if anybody knew of others that could positive ground or did they standardize themselves? it is no pressing matter anyway as it only applies to sunpower's systems at this time due to the design of their cells. this would be a bigger issue if sunpower were to sell cells and pvs on a small scale needing components pieced together rather than just complete whole systems being sold.

The Sunny Boy SB6000U that I received about one year ago supports both negative and positive grounding.