Replace a positive ground, Sunpower SPR-7000 to a transformer-less inverter

[oregon_phil]

So if I ...

-tighten all connections
-test each panel
-find one or more with little or no amperage
-replace those panel(s)

Then there is a chance my Sunpower inverter might work normally?

Joseph,

You never answered whether or not you are using the SMA DC disconnect switch. Is this the combiner you are referring to? I'm trying figure out what you changed. Now I'm thinking you did not change the SMA DC disconnect switch.

Since you installed your latest inverter, I have to assume you have installer privileges. On the installer webpage for your inverter, don't you have a DC Measurements page or something similar? If yes, the next time the power fluctuations happen, open up that webpage and take a video of the DC voltage and currents.

Your SMA 7000 US has one MPPT input. You have 4 strings of 10 panels connected in parallel. All strings should read exactly the same voltage since they are all connected together in parallel.

When you pulled out the fuse in the combiner box, is that the only thing you did? Did you look at the fuse terminals to see if there was any corrosion on it?

[bcroe]

We are neither Solar engineers nor are we the ones who physically installed the panels back in 2008. We relied on the expertise of the system design team. BTW, our panels face SOUTH and WEST. Inverter #1 is the one that failed and the one that has always been the bigger producer by about 25%. For all I know the configuration could be as you suggest, I just assumed each inverter did the job for each direction.

You can determine which arrangement you have, just by noting ihe inverter
outputs over a mostly clear day. If one rises and then declines sharply at a
different time of day than the other, they are connected to different orientation
panels. If they tend to track together, with a broader peak over half a day,
they are connected as I prefer. Bruce Roe

[Joseph.Unden]

So if I ...

-tighten all connections
-test each panel
-find one or more with little or no amperage
-replace those panel(s)

Then there is a chance my Sunpower inverter might work normally?

[DanS26]

Thanks for the advice DanS26. I did test every panel for voltage (they were very consistent). Does testing with the ampmeter tell me more about the health of the paAdobe? About a ddiode problem?

Yes, a solar panel is just like a battery....you may have a good voltage but no amps.

[Joseph.Unden]

Thanks for the advice DanS26. I did test every panel for voltage (they were very consistent). Does testing with the ampmeter tell me more about the health of the paAdobe? About a ddiode problem?

[DanS26]

If the problem returns.....you now will have to deal with intermittency. Best case a loose connection someplace....worse case a diode problem in one or more panels. Obtain a DC clamp on ammeter and track down the problem. At least you know now that it is not an inverter problem and looking on the bright side you now have a good backup inverter as a spare.

Good luck.

[oregon_phil]

Well, here is the latest in my story. Three days ago I switched out my Sunpower 7000 inverter (manufactured in 2008) for the "Certified Used" SMA 7000 I bought from Youlovesolar (manufactured in 2007) for $2300 & tax and shipping. This was an easy switch except for lifting the old one off and the "new" one onto the wall (they weigh 149 lbs each). There are 6 wires to reconnect and I knew where they went since the insides of the inverters are identical. The new inverter instantly started up after I turned on the AC & DC disconnects.

Everything sounded and looked good until about 11:30, when production got up to around 6000 watts. At that point my "certified used" inverter began to behave like my old one, cycling (derating) between the high 5000's to around 3,000 and back. Needless to say I was very disappointed. After a half hour of watching I went to my combiner box and disconnected one of the strings by pulling out a fuse. When I turned the system back on the inverter worked smoothly at around 4500 until it began to decrease due to darkness.

The next morning I went out and reconnected the forth string and went for a mountain bike ride. When I returned around noon the inverter was pumping out 6200 watts with no derating. I think the highest I observed that day was 6350 watts. I was excited!

I was home all day yesterday and the inverter appeared to work perfectly, producing more than 6000 watts most of the day.

Do these inverters adjust to the input ... reprogram or cure themselves?

Anyway, I have my fingers crossed ... hoping this good behavior continues!

By combiner box, do you mean the SMA DC-Disconnect box or do you have another combiner? Also, did you get a new SMA DC-Disconnect box with your new inverter or did you just use the old one?

[J.P.M.]

Well, here is the latest in my story. Three days ago I switched out my Sunpower 7000 inverter (manufactured in 2008) for the "Certified Used" SMA 7000 I bought from Youlovesolar (manufactured in 2007) for $2300 & tax and shipping. This was an easy switch except for lifting the old one off and the "new" one onto the wall (they weigh 149 lbs each). There are 6 wires to reconnect and I knew where they went since the insides of the inverters are identical. The new inverter instantly started up after I turned on the AC & DC disconnects.

Everything sounded and looked good until about 11:30, when production got up to around 6000 watts. At that point my "certified used" inverter began to behave like my old one, cycling (derating) between the high 5000's to around 3,000 and back. Needless to say I was very disappointed. After a half hour of watching I went to my combiner box and disconnected one of the strings by pulling out a fuse. When I turned the system back on the inverter worked smoothly at around 4500 until it began to decrease due to darkness.

The next morning I went out and reconnected the forth string and went for a mountain bike ride. When I returned around noon the inverter was pumping out 6200 watts with no derating. I think the highest I observed that day was 6350 watts. I was excited!

I was home all day yesterday and the inverter appeared to work perfectly, producing more than 6000 watts most of the day.

Do these inverters adjust to the input ... reprogram or cure themselves?

Anyway, I have my fingers crossed ... hoping this good behavior continues!

Thank you for the info and update.

I for one would be interested in hearing more as things progress.

J.P.M.

[Joseph.Unden]

Well, here is the latest in my story. Three days ago I switched out my Sunpower 7000 inverter (manufactured in 2008) for the "Certified Used" SMA 7000 I bought from Youlovesolar (manufactured in 2007) for $2300 & tax and shipping. This was an easy switch except for lifting the old one off and the "new" one onto the wall (they weigh 149 lbs each). There are 6 wires to reconnect and I knew where they went since the insides of the inverters are identical. The new inverter instantly started up after I turned on the AC & DC disconnects.

Everything sounded and looked good until about 11:30, when production got up to around 6000 watts. At that point my "certified used" inverter began to behave like my old one, cycling (derating) between the high 5000's to around 3,000 and back. Needless to say I was very disappointed. After a half hour of watching I went to my combiner box and disconnected one of the strings by pulling out a fuse. When I turned the system back on the inverter worked smoothly at around 4500 until it began to decrease due to darkness.

The next morning I went out and reconnected the forth string and went for a mountain bike ride. When I returned around noon the inverter was pumping out 6200 watts with no derating. I think the highest I observed that day was 6350 watts. I was excited!

I was home all day yesterday and the inverter appeared to work perfectly, producing more than 6000 watts most of the day.

Do these inverters adjust to the input ... reprogram or cure themselves?

Anyway, I have my fingers crossed ... hoping this good behavior continues!

[Joseph.Unden]

My panels all face the azimuth.

[edustys]

I do not consider this an optimum setup. The E and W facing panels cannot peak at
near the same time. If you wired half the E and half the W facing panels to one
inverter, same for the second inverter, you could use smaller inverters and the rest
of the AC setup. I was forced to this checkerboard arrangement here, to avoid
clipping on one inverter while the other was not working hard. Bruce Roe

We are neither Solar engineers nor are we the ones who physically installed the panels back in 2008. We relied on the expertise of the system design team. BTW, our panels face SOUTH and WEST. Inverter #1 is the one that failed and the one that has always been the bigger producer by about 25%. For all I know the configuration could be as you suggest, I just assumed each inverter did the job for each direction.

[bcroe]

the original wiring design is such that each inverter is wired separately and that the power generated by 22 (also 210 w each) south facing panels goes into inverter # 1 while the power generated by the 22 west facing panels goes into inverter #2.

I do not consider this an optimum setup. The E and W facing panels cannot peak at
near the same time. If you wired half the E and half the W facing panels to one
inverter, same for the second inverter, you could use smaller inverters and the rest
of the AC setup. I was forced to this checkerboard arrangement here, to avoid
clipping on one inverter while the other was not working hard. Bruce Roe

[DanS26]

These recent threads are the first I recall hearing about any industry shift from pos to neg ground. I have a sunnyboy 7000 tl-us from about 5 years ago I assume it is the newer neg grnd?
my other question is even if you had to convert to a newer neg gr inverter can't you still use a your old panels? Maybe just switch the string polarity going in and rewire the output? A bit of work but not terrible and then your back running on the newer std?
or is there something more to it?

Whoa...whoa....if you have positive ground Sunpower panels you just can't go switching wires around.......

[nomadh]

These recent threads are the first I recall hearing about any industry shift from pos to neg ground. I have a sunnyboy 7000 tl-us from about 5 years ago I assume it is the newer neg grnd?
my other question is even if you had to convert to a newer neg gr inverter can't you still use a your old panels? Maybe just switch the string polarity going in and rewire the output? A bit of work but not terrible and then your back running on the newer std?
or is there something more to it?

[oregon_phil]

edustys had two SB 4000US. At 240VAC, each inverter can put out a maximum of 17amps. So that's a combined total of 34 amps max. You have more amps.

At 240VAC, your SB7000 has a maximum AC continuous output of 30 amps. Configured properly, most standard 200 amp electrical panels can handle this without main breaker modifications. Using two SB7000's would cause you to make changes to your electrical panel. Exactly what, only your local jurisdiction would know. Check out the latest NEC 2020 for solar requirements. Search for the 120% rule.

Regarding your inverter derating, if you have user access, you can still get some AC & DC information off of the inverter. If you or a friend are into gadgets, you could use a thermal camera like a Seek to spot hot components inside of your inverter. Since you are an electrical type, you could double check all the wire connections in the DC disconnect and inverter when it's dark and in a safe manner. I'm not an installer or electrical type, but have a SMA 7.7 -40 inverter and like to pass on any insights when possible.