SunPower SPR-95: maximum string length?

Re: SunPower SPR-95: maximum string length?

From what I can (and cannot) see... My guess is the 95 watt solar panels have a "low" circuit voltage rating... In the US, we rate our "standard" line voltage components for 600 VAC maximum. In Europe, I have seen some 1,000 VAC ratings.

The Sunpower does not list their rated voltage either, but it could be as low as 70 VDC... Voc=21.5, so:

• 4xVoc=86 volts
• 86 volts * 1.25 typical NEC derating = 107 VDC
• 107 VDC * 1/sqrt of 2 (DC to AC peak voltage conversion) = 76 VAC rating

So.. My guess is the solar panel as a ~80 VAC maximum rating. So, you cannot place more than 4 of them in series because their insulation (and cell backing) is not rated for higher voltages...

Just a guess--You should call/email them and ask what their maximum system voltage rating is. The typical solar panel specifications should read something like:

• Framed modules certified by TÜV Rheinland as Safety Class II (IEC 60364) equipment for use in systems up to 1000 VDC
• Framed modules listed by Underwriter’s Laboratories for electrical and fire safety (Class C fire rating)
• 600V (IEC 61215 rating)

There is a TUV and UL rating for the SunPower Panel:

TUV-R: IEC 61215, Safety Class II Certified
UL Listed: UL 1703, Class C Fire Rating

I don't know the IEC / UL numbers -- So I don't know if IEC 61215 is a 1,000 Volt rating or if there are other allowed ratings...

-Bill

Re: SunPower SPR-95: maximum string length?

Hieronymous wrote: »

2. From your post, I now understand that the maximum voltage rating is determined by the isolation [should be insulation] and cell backing. I'm a bit surprised that it is so low. Do you have any idea why it is so low? Other, more powerful, SunPower panels are rated for 1000VDC.

I believe (perhaps guessing) that these were originally some of the earliest Sunpower panels... Perhaps they were designed for battery based systems (typically 12-48 volts) and this is continued production simply using the old materials/construction techniques--that were never "upgraded" for use with the standard GT inverters of today?...

3. I don't exactly understand how a single panel in a string of for example 6 panels, clearly exceeding the rating in your example of 80VAC, can be damaged by overvoltage. Where, or how i.e. in which circumstances, can a too high voltage drop arise in one of the panels of this 6 panel example leading to permanent damage?

I believe it is the issue of "system safety", not damage to the panels specifically.

Normal electric code (US) basically uses 600 VAC as the minimum safety design for our 120/240 VAC (or higher) electrical systems. The testing of appliances (and wire insulation) is (as I recall) done at 3xRated voltage--Or in this case 1,800 VAC (we can also pass the test with sqrt of 2 x 1,800 volts--typically used when our equipment had Radio Frequency grounding capacitors--No AC 50/60 Hz leakage currents).

So--In this case, either the panels were never designed to take 1,800 VAC production tests, or there could be "insulation punch through" to the metal frame and/or through the backing... Or, they simply never tested to 600 VAC and bothered getting the UL/TUV/CSA/NRTL listings for that high of voltage.

4. From the IEC 61215 documentation, I understand that it is about standardized testing methods independent of a panel's actual maximum system voltage. It only states how this should be tested.

That was my guess too... Need the rated voltage to complete the panel specification.

Will the panels system work OK at your 155 Volt system maximum (or less, because you only want 6x panels in series)... Probably--They should have been tested at 3x70v=210VAC (or VDC). (This is a common mode test--i.e., one lead of XX votlage from the tester to attached to "both +/-" leads; and the second tester lead to Panel Metal (aluminum frame, possibly some sheet metal/mesh to the real of the unit) to look for that failure (arc, leakage current, etc.).

However, it is a (small?) gamble. Solar panels are mounted outside in wind/sun/hot/cold/rain/salt air/dust/dirt/etc... I have no way of establishing if there would be a hazard or not. And, I don't have any information on the connection box (or pig tail wires) as to what voltage/application they were designed to support.

Sort of the equivalent of using 12 volt wiring and switches for cars to wire your home... Not usually a good idea.

-Bill