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

[edustys]

oregon_phil,

Thanks for your insightful comments. You obviously have worked with solar systems.

SMA says this about derating ...

Temperature derating occurs for various reasons, including the following:

• The inverter cannot dissipate heat due to unfavorable installation conditions.
• The inverter is operated in direct sunlight or at high ambient temperatures that prevent adequate heat dissipation.
• The PV array and inverter are mismatched (power of the PV array compared to the power of the inverter).
• If the installation site of the inverter is at an unfavorable altitude (e.g. altitudes in the range of the maximum operating altitude or above Mean Sea Level, see Section "Technical Data" in the inverter operating manual). As a result, temperature derating is more likely to occur since the air is less dense at high altitudes and thus less able to cool the components.
• A constantly high DC voltage (V_MPP) is present at the inverter.

I don't think any of these apply to my situation.

I live in Southern California (altitude approx 400 feet) and my inverter has been located in my garage since installed in 2009. The temperature in the garage is never excessive, especially now during the winter. The inverter is derating as we speak and the temperature in my garage is 65 degrees Fahrenheit.

I have removed and cleaned the fans. I have used the jumpers to do the fan test and have observed the fans blowing while the unit is derating.

My panels are producing about 430 DC volts, well within the range listed in the specs (250-600 V DC)

My panels produce approximately 8400 watts (40 panels at 210 w each). The Inverter specs list the max array input power at 8500 watts.

I am not an installer. I have quite a bit of experience (built and wired my own house and other structures) and like to research projects, but do not claim to be a solar professional. I will look into trying to access the log or find someone who does.

Since the my last post the SMA tech has gotten back to me and recommended using the "new" inverter (not two inverters). But I would still like to know how edustys! uses two inverters.

Thanks again,

Hi Joseph,

I have been following your journey through the maze that is solar energy with great interest. I wasn’t sure if you were asking me about why I had 2 inverters until I was actually referenced in your last reply.

All I can tell you is that 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. When the inverters were replaced, it was a simple swap out and reconnect not requiring any additional intervention or equipment. Each inverter had its own DC Disconnect which was able to be reused on the new replacements.

My system was installed in 2008. It’s quite possible that the larger capacity inverters were not as plentiful then or maybe the dealer just had a lot of SPR-4000m’s on hand. I do know that the 210 w panels were probably being fazed out in favor of 245 (?) w panels which were a lot more expensive at the time. Either way, inverters manufactured before 2012 came with only a 10 yr warranty while those produced after 2012 come with a 25 yr warranty. Live and learn.

[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.

[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?

[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.......

[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

[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.

[Joseph.Unden]

My panels all face the azimuth.

[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!

[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.

[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?

[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.

[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]

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]

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?

[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