[RE-wrenches] Sunpower off grid?

[Larry Crutcher, Starlight Solar Power Systems]

Hello Ray,

I have been installing SunPower cell modules for about a decade. All of our mobile installations are ungrounded arrays, off grid we use negative ground. We have never had any issue using them to charge batteries up to 48 volts, even when combined in series. I have not installed any for grid tie.

Last year I purchased about 100 of the 327 and 435 Watt modules, likely from the same seller, for a very low price. There is no SunPower label on the back. I was told that these modules were laminates that SunPower rejected due to cosmetic flaws. The surface has lots of blemishes clearly visible under the glass. Someone other than SunPower made frames and assembled the module. The frame quality is not so great and the 435 structurally feels inadequate. I sell these to off grid customers in Mexico that want cheap but high performance PV solar power.

That’s all...

Larry Crutcher
Starlight Solar Power Systems




On Aug 20, 2014, at 10:46 PM, Ray Walters <ray at solarray.com> wrote:

Greetings fellow Wrenches;

I have a customer that just purchased some Sunpower E20 -435 modules somehow from Ebay, and wants me to design a backup power system for him.
This system would be battery based and not be grid tied.  SO the question is: has Sunpower put to rest the positive grounding issue with these modules?
I would want to either use a negative ground system or go ungrounded, as the charge controllers and battery based inverter do not play well with a positive grounded system.
My idea is that I could run these modules at lower voltage, either all in parallel (85.6 Voc) or 2 in series (191 Voc) with Midnite Classic controllers, and that the whole surface polarization issue will be minimized at these lower voltages.
I know this came up before, and Sunpower basically said they would revoke their warranty for any battery based systems, (which is why I'm no longer a Sunpower dealer.... :)
Don't the newer Sunpower modules no longer need positive ground, and if so, which models is this true for?  In this case, the warranty is already suspect, so that's not an issue.  It just has to work safely.

Thanks in advance for your help,

-- 
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760