New inverters compatible with old Sunpower positively grounded panels?

ToddF

I have a 12 year old system with over 200 Sunpower SPR-305-WHT-U modules which are positively grounded. The old transformer based inverters were set up for positive grounding. All ten inverter are defunct and as far as I can find nobody makes a transformer based inverter anymore. Anybody seen this issue and have a solution? There are thousands of these panels installed worldwide. PS Sunpower had no solutions.

DanS26

Try contacting Fronius....they put the SunPower badge on their transformer based inverters.  You can still find Fronius transformer inverters hit or miss...here or there.   The trouble is you need a bunch.

Fronius USA is located in northern Indiana....give them a call...a good group of people.

Solar Guppy

The panel connections are isolated from the frame rails which are at ground potential. You can use any off the shelf grid tie inverter with the Sunpower panels, but may see a 3-5% lower power harvest from the panels. Since they are decades old, probably won't make any measurable difference in annual harvests at this point.

ToddF

DanS26 said:

Try contacting Fronius....they put the SunPower badge on their transformer based inverters.  You can still find Fronius transformer inverters hit or miss...here or there.   The trouble is you need a bunch.

Fronius USA is located in northern Indiana....give them a call...a good group of people.

Dan,  I have been in extensive contact with Fronius who did indeed make the inverters. They no longer sell a transformer based inverter but do have a repair service where I can send my defunct units. They say the cost is around half that of a new inverter with a one year warranty (I think). That will be my fall back solution because I don't want to spend that much money, plus shipping both ways, plus labor, to have them start kacking out again a couple years later.

ToddF

Solar Guppy said:

The panel connections are isolated from the frame rails which are at ground potential. You can use any off the shelf grid tie inverter with the Sunpower panels, but may see a 3-5% lower power harvest from the panels. Since they are decades old, probably won't make any measurable difference in annual harvests at this point.

Guppy,
Thanks for responding. I'm not clear on the concept but those modules had both + and - terminals on the back side of the cells which I believe made a positive charge build up on the top side of the cell. That worked contrary to voltage flow thus decreasing it. I believe the positive grounding swept off the positive charge so full voltage flowed. I was under the impression that the problem made a big dent in the total output power. It is a 12 year old system with expected degradation so a 3-5% hit would be nada. Can you please explain why you believe the loss is so minimal???  I would love to be able to just buy new transformerless inverters and plug them in.  Thank you!!!

DanS26

Since you are in contact with Fronius.....just ask them if their new transformer less inverters will work out of the box with the positive ground Sunpower panels.  If anyone would know the correct answer it would be Fronius.

DanS26

Just an idea....but if you or someone you know with electronics knowledge could part out two or three of the non working inverters to repair the remaining 7 or 8 inverters....maybe get a few more years out of your inverter investment.

Solar Guppy

You can use any off the shelf gridtie inverter. The whole purpose of the positive ground was some theoretical science that would possibly have slightly lower degradation of the panels overtime. No one else has ever done it since.

The current crop of non-isolated inverters will work just fine with your old panels, I'm currently using a pair of Solis 5G's, you may want to look at the 4G line, best bang for the buck on the market and rock solid performance.

Search for Solis-1P10K-4G-US-SPRT online. You should be able to easily replace the 10 inverters with 6 of these ( or less ), they have 4 mppt channels in a 10kw box that is convection cooled, no fans needed.

If this installation is 3-phase, Solis has larger units starting at 75kw that might be a better fit. https://www.ginlong.com/us/inverter.html. 

ToddF

Solar Guppy said:

You can use any off the shelf gridtie inverter. The whole purpose of the positive ground was some theoretical science that would possibly have slightly lower degradation of the panels overtime. No one else has ever done it since.

The current crop of non-isolated inverters will work just fine with your old panels, I'm currently using a pair of Solis 5G's, you may want to look at the 4G line, best bang for the buck on the market and rock solid performance.

Search for Solis-1P10K-4G-US-SPRT online. You should be able to easily replace the 10 inverters with 6 of these ( or less ), they have 4 mppt channels in a 10kw box that is convection cooled, no fans needed.

If this installation is 3-phase, Solis has larger units starting at 75kw that might be a better fit. https://www.ginlong.com/us/inverter.html. 

Guppy,  I have never used Solis but have lots of SMA Sunnyboys out there. There are four on a separate array of this same system and they are all still working.  Any opinion of SMAs? 
It is a 3-phase system but it is using a mix of ten 8k and 6.5k Fronius and four 5k SMAs, all single phase inverters balanced on each leg.  I wouldn't do that again because one bad inverter can throw off the whole system. I think I may pull the old SMAs and go with 3 phase all around.

Solar Guppy

SMA is 1st tier, but don't have the $/Watt of other brands. 

Solis is the largest string inverter company out of China and been around for close to 20 years, there are US retailers that carry them, I use one from Texas for the 5'g's I own.

With a single 75K unit you could replace everything for half the price of 10 inverters, but I'm not trying to promote a brand, just the options I'm familiar with. With code requiring RSS and / or optimsers or shutdown per panels for new system, not many options for string inverters these days.

Cantinman22

Solar Guppy said:

You can use any off the shelf gridtie inverter. The whole purpose of the positive ground was some theoretical science that would possibly have slightly lower degradation of the panels overtime. No one else has ever done it since.

The current crop of non-isolated inverters will work just fine with your old panels, I'm currently using a pair of Solis 5G's, you may want to look at the 4G line, best bang for the buck on the market and rock solid performance.

Search for Solis-1P10K-4G-US-SPRT online. You should be able to easily replace the 10 inverters with 6 of these ( or less ), they have 4 mppt channels in a 10kw box that is convection cooled, no fans needed.

If this installation is 3-phase, Solis has larger units starting at 75kw that might be a better fit. https://www.ginlong.com/us/inverter.html. 

Hi Solar Guppy.  Thank you for your insights.  I've been trying for months now to find a solution to these positively grounded systems.  Can you elaborate on how you connected these inverters to the positively grounded mods and made them produce?  We've been unsuccessful up till now.

DanS26

I too would like to know how Solar Guppy got those negative grounded inverters to work with positive grounded panels.

Dave Angelini

Another way is to use a Schneider 600v battery based MPPT. It can be positive, negative or floated. I have done this several times to use the old Sunpower panels. They often are sold on EBay to the unsuspecting. They are a really well made panel and often meet specs far longer than their warranty.

 They,  the Sunpower (+ ground) panels really are old now BTW.

 Many people are wanting a battery based system these days and you would have to make sure it is legal for insurance if you carry it. One way around that is to ground mount the array. You need to check on this for your area and situation!