Greetings from cloudy Frederick, MD

[websterize]

Having a commissioned Webster Solar Billboard by April 30 would exceed my expectations.

[Naptown]

Then it sounds like they are doing the right thing.
Consider the unplugged module as a spare for just in case.
40 x 255 = 10,200W
39 x 260 = 10,140W so with the increase in module wattage you in reality only lost 60W

Yes they are a major competitor in my market. That doesn't mean I am going to make up fairy tales and trash them for no reason. The 40 modules on 3 inverters is what caught my attention. The rest came from a quick look at the SMA site and doing the calculations.
As long as you are OK with the final product and satisfied then that is what matters.
As far as being skeptical that is a good thing it makes you dig into what a salesman tells you, although before you sign on the dotted line is a better time to do the research.
At this point the only things I could fault them for would be not telling you up front that there would be 1 unplugged module and the installed wattage would be less than promised. I understand that people make mistakes, it's how they correct them that matters.
The thing that got my goat was a statement you made in an earlier post to the effect of they scrutinize the engineering very carefully and the manufacturer also checks the integrity of the design. This obviously had not happened or was done incorrectly. Too many mis steps in the process for that to happen.
Are they still exceeding you expectations?

[websterize]

You still have a problem. Maximum # of those modules on is 13. What happens to module 40. Disconnected?

Yes, confirmed today: design is 13 modules per string, for a total of 39. The 40th panel was left unplugged deliberately. I guess I'd feel better about this if they had disclosed that from the start, but they did not. Granted, the array would look odd with three rows of 10 and one row of 9, but these panels aren't cheap. The fit and finish of the project turned out exactly as promised, but as you correctly pointed out, technically we paid for a 10.4 kW system, not a 10.14 kW system.

I urge you to go to the SMA website. download Sunnydesign and plug in the numbers for yourself.

I tried, weeks ago, but SMA marginalizes users of Mac OS X. I don't own a Windoze PC.

[QUOTE=Naptown;44223]Atis Sun is not giving you good advice. Admittedly changing to the Fronius inverter would be more work for them. But this is a workable and safe solution that will give you the full output of your system. Remember I said earlier that inverters run at their most efficient when operating at near peak input.

[Naptown]

Vmmp is 30.9, according to the spec sheet.

The owner of the company that did the electrical work called. The SB3000US (500V) inverters are coming off, and three SB3000HF-US (600V) are on order. Apparently, there was confusion with the similar model number in the Sunny Boy line. (I think the HF inverters are Sunny Beam-ready!)

You still have a problem. Maximum # of those modules on is 13. What happens to module 40. Disconnected?
At 14 on a string the odds of frying that inverter go way up or just pray the temperature stays warm.

They still have not come up with a workable solution that utilizes ALL the modules you purchased and paid for or if they do you run the risk of frying one of the inverters.
This is the easiest/cheapest solution for them as they probably have the strings set up in this manner.
For you who purchased and paid for the system to be installed properly you should insist that it at least be done properly.
I urge you to go to the SMA website. download Sunnydesign and plug in the numbers for yourself.
Atis Sun is not giving you good advice.
Admittedly changing to the Fronius inverter would be more work for them. But this is a workable and safe solution that will give you the full output of your system.
Remember I said earlier that inverters run at their most efficient when operating at near peak input. The Fronius is essentially a three stage inverter. Meaning there are three steps to the size meaning when power is reduced from the array the inverter will go to a lower stage keeping the efficiency at it's peak
In short more harvest

[websterize]

But just to double check what is the Vmp on that module.

Vmmp is 30.9, according to the spec sheet.

The owner of the company that did the electrical work called. The SB3000US (500V) inverters are coming off, and three SB3000HF-US (600V) are on order. Apparently, there was confusion with the similar model number in the Sunny Boy line. (I think the HF inverters are Sunny Beam-ready!)

[Naptown]

[QUOTE=websterize;44205]Rich, Matt Bartlett, who owns AtisSun, just called. They're on the inspection fail and seem committed to making everything right. Appears they'll do whatever needs to be done to make this right. Still awaiting details on the system design from his colleague, Mark.

After reading John Wile's PV Math piece on solar and cold weather, I think I get the Voc issue you've been flagging from the start. (Really do appreciate all your feedback -- this topic is getting a lot of views!). Running the spec sheet data on our 260W x 40 array, the Voc on each 260W panel is 37.9V, with a temperature coefficient of -0.36 Celsius. According to Solar America Board for Codes and Standards, the expected lowest temperature nearest Frederick is -14

[websterize]

Rich, Matt Bartlett, who owns AtisSun, just called. They're on the inspection fail and seem committed to making everything right. Appears they'll do whatever needs to be done to make this right. Still awaiting details on the system design from his colleague, Mark.

After reading John Wile's PV Math piece on solar and cold weather, I think I get the Voc issue you've been flagging from the start. (Really do appreciate all your feedback -- this topic is getting a lot of views!). Running the spec sheet data on our 260W x 40 array, the Voc on each 260W panel is 37.9V, with a temperature coefficient of -0.36 Celsius. According to Solar America Board for Codes and Standards, the expected lowest temperature nearest Frederick is -14

[Naptown]

OK from what I see from the photo's a main breaker could be added to the combiner panel. this is a good thing.
So from what I can see to fix your system the following comes to mind
1- replace inverters with the 600V rating inverters
2- disconnect one panel for a total of 39
3- add main breaker to sub panel@ 50 A and do a line tap connection. ( keep in mind this is considered a separate service and grounding requirements will prevail)
4-install a line tap connection to the main panel
5- Maybe add a revenue grade meter between the solar panel and the line taps. (Check with aggregator to confirm)

[websterize]

Then if there is room in that box for another 2 pole breaker it will make a line tap easier. I assume the inverters are outside?

Yes, inverters are outside the house: http://flic.kr/p/byyi21

I was looking at aggregating SREC's and what I could find is for systems over 10KW in Maryland they are requiring a revenue grade meter installed which you will have to read once a month and report. The readings from the inverter are not accurate enough apparently. I do not have anything out there right at 10KW DC and have not called the aggregator to check the requirement and the specifics. This is something you would want to do before you make the last payment.

Roger that. We have already paid in full.

[Naptown]

Thanks, Rich. Wouldn't replacing the SB3000US inverters (500Vmax) with the SB3000HFUS (600Vmax) and leaving one of the 40 modules unplugged solve the cold weather voltage problem?

Yes




Yes, I believe option C above is fairly accurate.

There is a PV disconnect box for the utility on the outside of the house below the power meter. Inside, in the basement, the main circuit breaker is indeed 200A, and there is a 50A breaker at the bottom (labeled PV in this photo). Below the main breaker is a PV inverter sub panel with three, 20A breakers.

Then if there is room in that box for another 2 pole breaker it will make a line tap easier. I assume the inverters are outside?
I was looking at aggregating SREC's and what I could find is for systems over 10KW in Maryland they are requiring a revenue grade meter installed which you will have to read once a month and report. The readings from the inverter are not accurate enough apparently. I do not have anything out there right at 10KW DC and have not called the aggregator to check the requirement and the specifics. This is something you would want to do before you make the last payment.

[websterize]

[QUOTE=Naptown;43583]I had a bit of time today to run some numbers on your inverters and panels.

[Naptown]

Rich, he appeared to echo what you have said about the inverter math not making sense, and he mentioned the cold-weather volt inverter issue -- problems could occur once the temperature drops to 30 degrees F, higher than the 14 F you said would fry the inverters. He wrote three comments on the electric report:

"1- String size over 500 Vdc per inverter" [He noticed the placard reads 600Vdc, but the inverter nameplate says 500 V max.]
"2- 3,380 watt per string is more than 3,000W max inverter rating" [I think he's assuming 13 x 260W; one string could be 14 x 260. There are 40 x 260W modules total.]
"3- 50 amp backed is more than 20 percent bus rating." [No idea what this means, but it sounds ominous.}


No, but I said there were most likely 13 or 14 modules per string. I have not seen the stringing calculations from the installer.

To address comments by Inspector
1) This is what I have been telling you Too much voltage on the inverters The max I would go would be 11 modules on one string on each inverter.

2) Well if this is the case It really is not a problem. Inverters should be sized +/- 20% meaning a 3000 Watt inverter is good from 2400W to 3600W In your inverter's case The max STC input is 3750W (from SMA spec sheet)
The reason is because once you get outside the 20% you start to lose harvest. Above the rating and the inverter will clip meaning it will throttle back the input to protect itself. Below the 20% and the inverters work at a lower efficiency. They like to be right up on the peak power for the highest efficiency. Both will result in losses in harvest.

3) As far as the circuit breaker going into the panel goes
You most likely have a 200A service panel
As the code reads the sum of all overcurrent devices feeding a panel shall not exceed 120% of the rating of the buss bars. In addition the feed from the solar array must be located at the opposite end of the buss bars from the main breaker.
In your case there are really three options.

A) reduce the circuit breaker for the solar in the panel to a 40A. The combined output of the three inverters is 39A. This in my opinion is cutting things a bit too close. There is a potential of nuisance tripping.

B) Replace the main circuit breaker with a 150A breaker. This will meet the code requirement however it could also cause the main to trip under certain conditions. (Cold and cloudy heatpump and backup heat running water heater runnning etc)
This solution may also violate the load calculations on the house.

C) Really the only viable option is to do a line tap connection. This is where the solar is tied into the wires between the meter and the main breaker in the panel. Now if per chance they wired the three inverters together into a breaker box on the exterior of the house and then fed to the main panel and tied into the 50 A breaker. (This is most likely what was done as this will also serve as the utility disconnects which the utilities like to see near the meter.) If that is the case then they will have to add another disconnect between the main panel and the outside box. The reason is that this is considered as another service and all service disconnects must be grouped together.

Keep working on getting the string wiring You have a serious problem.

The only solution I could come up with to make this work without having to tear out the inverters that are in place is to add one more and put the array on 4 inverters in strings of 10 modules.
This is slightly below the sweet spot of these inverters and will cause minor harvest losses but it will be a safe installation meaning nothing will fry. With 10 modules per string and inverter the inverter is just beyond the 20% at 21%. Not ideal but not entirely out of the ballpark either.

Now this bring up the next issue which is at that point you will have 4 inverters to replace down the road. My recollection (We don't do many of these small inverters) is that they go for about $1800 each. Which mean down the road you are looking at about an $8000.00 Plus maintenance cost at about year 13. I surely hope they told you about this.
The good news is that SMA does offer extended warranties. They cost almost as much as an inverter but they are available. I would insist your installer provide you with the extended warranties preferably at no additional cost to you.

[websterize]

he has been previously told.
he could also be running his electric bill up running it. Many of the meters that look analog are actually reading a magnetic impulse from the wheel. Wheel spins backwards meter still counts up.
his house may just be new enough to have one of these meters.

I pulled last month's electric bill, which showed a 30kWh daily average. Since then, with the array online while we await electric inspection and installation of the net meter, our daily kWh average has nearly doubled. You were right, Rich. Array is dark until we get the net meter.

[websterize]

What did the inspector fail you for?
70% of the time it is lack of knowledge on the inspectors part.
The other 30% is usually for dumb things.

Rich, he appeared to echo what you have said about the inverter math not making sense, and he mentioned the cold-weather volt inverter issue -- problems could occur once the temperature drops to 30 degrees F, higher than the 14 F you said would fry the inverters. He wrote three comments on the electric report:

"1- String size over 500 Vdc per inverter" [He noticed the placard reads 600Vdc, but the inverter nameplate says 500 V max.]
"2- 3,380 watt per string is more than 3,000W max inverter rating" [I think he's assuming 13 x 260W; one string could be 14 x 260. There are 40 x 260W modules total.]
"3- 50 amp backed is more than 20 percent bus rating." [No idea what this means, but it sounds ominous.}

Did the inspector ask for string calculations?

No, but I said there were most likely 13 or 14 modules per string. I have not seen the stringing calculations from the installer.

[Naptown]

If it failed, why is it still on line ? You are only allowed to power it for testing till it's approved.

he has been previously told.
he could also be running his electric bill up running it. Many of the meters that look analog are actually reading a magnetic impulse from the wheel. Wheel spins backwards meter still counts up.
his house may just be new enough to have one of these meters.