Confusion on output

christian09 · January 2013

Hi,
I have a fronius 7.5 ig plus with 33 solar world 235kw panels.
I live in Tampa, FL. The panels are installed at a 23 degree angle west facing, with a 270 azimuth.
I was told by a solar professional that during a January day, I should be peaking out at around 5000-6000 on my inverter readings, but the highest it ever goes is around 3200.
Am I being told the correct info?
He believes the "wiring" is incorrect. I have no idea, so any help would be great.

Cariboocoot · January 2013

Re: Confusion on output

Well let's check the numbers.
Thirty-three 235 Watt panels is 7755 Watts. At typical 77% averaged output it should be capable of 5.9 kW. So 3200 Watts is quite low.

Wiring problems? Could be. Without knowing how the array is laid out and what size/length wiring is used it's hard to say.

You can put your system's specs into PV Watts http://www.nrel.gov/rredc/pvwatts/grid.html and check what it says about expected output.

christian09 · January 2013

Re: Confusion on output

Thank you Cariboocoot.
I just wanted to verify that number. My only issue is how to have someone competent come out and check my system for a fair price. I will call solarworld and fronius to attempt to narrow it down. And will try to get the size an legnth of wiring along with the layout....can I post this info in this thread?
Thanks

NorthGuy · January 2013

Re: Confusion on output

christian09 wrote: »

I was told by a solar professional that during a January day, I should be peaking out at around 5000-6000 on my inverter readings, but the highest it ever goes is around 3200.

At what time of the day do you get the peak with your West-faced array?

Cariboocoot · January 2013

Re: Confusion on output

christian09 wrote: »

And will try to get the size an legnth of wiring along with the layout....can I post this info in this thread?
Thanks

By all means. It is not difficult to see if some major mistake has been made such as too high/low string Voltage or wire size too small for the length causing excess Voltage drop.

I'm pretty sure those Solarworld panles have a Vmp of about 30 and Imp around 7.5 to 8. The Fronius has an input range of 230 to 500 (245 at start-up) so I'd expect ten panels per string at least. With 33 panels total, it's probably three parallel strings of 11 in series (330 Vmp & <24 Imp). That should not be difficult to handle.

Possible one of the strings has become disconnected? Each should have its own breaker or fuse at the combiner box; it may be tripped/blown.

The West-facing array will be subject to greater heating so that would reduce the Voltage some, but your output numbers do look to be far off expectations.

BB. · January 2013

Re: Confusion on output

Time for the broken record... I would suggest getting a DC Current Clamp Meter like this one from Sears for around $60 (actually an AC/DC Current Clamp digital multi meter--"Good Enough" for our needs around here). You can clip on one wire from each solar PV string and measure the individual currents. Will tell you if one string is having problems or not (they should all match current pretty closely unless there is an electrical problem or shading on the array).

If you have three or more parallel strings, there should be a combiner box--If it has breakers, you can turn off one breaker at a time and read the current from your inverter's display too.

-Bill

Photowhit · January 2013

Re: Confusion on output

Where in Florida are you?

I think we have a solar installer contributer who works Tamps south, named Solar Guppy? Might be worth sending a PM.

christian09 · February 2013

Re: Confusion on output

My Peak is around 2-3pm eastern.

christian09 · February 2013

Re: Confusion on output

Photowhit wrote: »

Where in Florida are you?

I think we have a solar installer contributer who works Tamps south, named Solar Guppy? Might be worth sending a PM.

Thanks Photowhit,
I am an Sarasota, which is about 50 min. south of Tampa, I will send him a message. Thanks.

christian09 · February 2013

Re: Confusion on output

Cariboocoot wrote: »

By all means. It is not difficult to see if some major mistake has been made such as too high/low string Voltage or wire size too small for the length causing excess Voltage drop.

I'm pretty sure those Solarworld panles have a Vmp of about 30 and Imp around 7.5 to 8. The Fronius has an input range of 230 to 500 (245 at start-up) so I'd expect ten panels per string at least. With 33 panels total, it's probably three parallel strings of 11 in series (330 Vmp & <24 Imp). That should not be difficult to handle.

Possible one of the strings has become disconnected? Each should have its own breaker or fuse at the combiner box; it may be tripped/blown.

The West-facing array will be subject to greater heating so that would reduce the Voltage some, but your output numbers do look to be far off expectations.

I will do my best to check some of this and the wiring diagram/wire type and length are on the way.
One thing I noticed this weekend, when my verizon internet/tv went out...it was blown out when the solar guys turned the 4 switch breaker off, which I find out has my verizon fios, sprinkler system, and a couple more outlets on it. Is it ok to have other items on the same breaker as the solar system?thanks in advance

Cariboocoot · February 2013

Re: Confusion on output

christian09 wrote: »

Is it ok to have other items on the same breaker as the solar system?thanks in advance

Absolutely not.
The output from a GT inverter needs to have its own dedicated line and breaker connected to the main service panel.

NorthGuy · February 2013

Re: Confusion on output

christian09 wrote: »

My Peak is around 2-3pm eastern.

At the peak, the sun is at about 50 degrees to the panels, so you will get only cos(50) = 65% of your maximum output, which is about 5000W. This is in ideal atmospheric conditions with panels at 25C and with 100% efficiency. If you remove 20% for not ideal atmosphere and 5% for efficiency, this will give you 3800W. If panels are hot (as I guess their would be in Florida at this time), production may decrease about 15, even 20%. So, 3200W peak sounds about right.

I have SolarWorld panels too, and checked them many times with solar meter. They always produce at or slightly better than expected based on available solar energy.

christian09 · February 2013

Re: Confusion on output

Thank you Cariboocoot.
I have attached my wiring diagram...I had to piecemeal it together. Thanks again.Attachment not found.

Cariboocoot · February 2013

Re: Confusion on output

From what I can make out of that layout, you have a very Westerly facing array which would miss about half the day's solar (depending on roof pitch and sun angle). There appear to be three strings of panels randomly grouped together, with some in one row and some in another. Heaven only knows what any shading may do to that set-up.

I hate to say it, but I think you're sort of shot in the foot here as the array is subject to only some daylight hours and those at the hottest time of the day. The panels probably never see optimum insolation and therefor could not be expected to put out their maximum. Did they warn you about this? What kind of power production was promised? Without reconfiguring the entire system I don't see any way that's likely to improve things. As it is, I don't think it's a case of one string being disconnected or badly wired. That sort of thing can be fixed. Correcting this would be very expensive, as essentially you'd be uninstalling everything and starting over.

We're it me, I'd have chosen micro-inverters for that install and put some on the East-facing roof and some on the South-facing gable roofs as well as some on the West-facing roof. That way you'd get production over more hours and probably a higher total Watt hours per day even though peak production Watts would not be as high.

christian09 · February 2013

Re: Confusion on output

Thanks,
In the fine print of the contract it says west facing it could be significantly reduced. I was going off the quote the salesperson showed me, then of course the contract says something different. Shame on me, I'm in sales and see the competition do this to others too. This contract is a nightmare for the buyer. I want to look for ways to enhance this system. I heard of using mirrors? any suggestions?thanks

Cariboocoot · February 2013

Re: Confusion on output

christian09 wrote: »

Thanks,
In the fine print of the contract it says west facing it could be significantly reduced. I was going off the quote the salesperson showed me, then of course the contract says something different. Shame on me, I'm in sales and see the competition do this to others too. This contract is a nightmare for the buyer. I want to look for ways to enhance this system. I heard of using mirrors? any suggestions?thanks

The cost of trying to reflect light on to the existing panels would probably be equal to and more problematic than putting up more panels. How much more are you willing to spend to get it to work?

You need to find a local installer who won't snow you that can help you work out some viable options. I'm not sure about the Fronius' "front end" - whether it has two or more MPPT inputs or just one - but it might be possible to move some of the panels to the other side (beware of roof damage) and keep them connected to the same inverter. Otherwise it's move or more panels and additional inverter.

One thing that should be done is figure out how many panels could be placed on the East side, and then use PV Watts to compare potential output values with the different configurations to find the most kW hours per day. I doubt you will be able to 'time' this for TOU rate structure (may not matter where you are), so you're just going to have to take what you can get.

Might be able to sell the 7.5 kW inverter and buy a combination of smaller ones for any new configuration.

Sorry, there just doesn't seem to be any simple solution here.

BB. · February 2013

Re: Confusion on output

Using PV Watts for Tampa and 7,755 watt array (rest defaults):

South:

"Station Identification"
"City:","Tampa"
"State:","Florida"
"Lat (deg N):", 27.97
"Long (deg W):", 82.53
"Elev (m): ", 3
"PV System Specifications"
"DC Rating:"," 7.8 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 6.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 28.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.0 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.56, 796, 71.64
2, 5.21, 814, 73.26
3, 5.72, 975, 87.75
4, 6.52, 1052, 94.68
5, 5.92, 977, 87.93
6, 5.56, 875, 78.75
7, 5.46, 882, 79.38
8, 5.70, 933, 83.97
9, 5.32, 842, 75.78
10, 5.41, 899, 80.91
11, 4.83, 796, 71.64
12, 4.24, 735, 66.15
"Year", 5.37, 10577, 951.93

West:

"Station Identification"
"City:","Tampa"
"State:","Florida"
"Lat (deg N):", 27.97
"Long (deg W):", 82.53
"Elev (m): ", 3
"PV System Specifications"
"DC Rating:"," 7.8 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 6.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 28.0"
"Array Azimuth:","270.0"

"Energy Specifications"
"Cost of Electricity:"," 9.0 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.16, 535, 48.15
2, 3.95, 605, 54.45
3, 4.77, 805, 72.45
4, 6.01, 959, 86.31
5, 6.02, 988, 88.92
6, 5.49, 856, 77.04
7, 5.19, 830, 74.70
8, 5.19, 837, 75.33
9, 4.41, 688, 61.92
10, 4.18, 682, 61.38
11, 3.44, 547, 49.23
12, 2.88, 477, 42.93
"Year", 4.56, 8808, 792.72

East:

"Station Identification"
"City:","Tampa"
"State:","Florida"
"Lat (deg N):", 27.97
"Long (deg W):", 82.53
"Elev (m): ", 3
"PV System Specifications"
"DC Rating:"," 7.8 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 6.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 28.0"
"Array Azimuth:"," 90.0"

"Energy Specifications"
"Cost of Electricity:"," 9.0 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.11, 525, 47.25
2, 3.85, 592, 53.28
3, 4.81, 817, 73.53
4, 6.02, 962, 86.58
5, 5.91, 971, 87.39
6, 6.01, 946, 85.14
7, 5.88, 953, 85.77
8, 5.61, 912, 82.08
9, 4.83, 758, 68.22
10, 4.20, 687, 61.83
11, 3.34, 535, 48.15
12, 2.78, 465, 41.85
"Year", 4.70, 9123, 821.07

Both East/West is significantly lower power production--And Solar Guppy (Florida) found that a south-east facing array produces more power because of cooler time of day and lost afternoon production due to afternoon clouds/thunder storms.

But that is not all--In (for example) California, we have to use Time Of Use billing--Which means that afternoon/evening power costs in summer are ~$0.30 per kWH (or higher) vs ~$0.09 per kWH for off peak times (and ~$0.12 Watts in winter peak time)...

For us, optimizing summer afternoon power production can gives us ~3x more "$$$ credits" even if overall yearly production in kWH is less.

-Bill

Confusion on output

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