String Sizing SMA 6000 and SolarWorld 175s

newenergy

Does anyone see a problem with 3 strings of 11 SolarWorld 175s with the SMA6000US 240V?

The SMA string sizer thinks it's ok, but there are some yellow numbers in the predicted outputs.

However, the yellow number are on:

Max Open Circuit Voltage vs. lot temp
It never exceeds NEC - It never exceeds the MPPT range for record lows - It's never going to be Open Circuit - It's very rarely even below 50 degrees here when the sun is shining.

There are a fair amount of yellows in the total production for 3 strings, but they start going yellow at 5184W, which seems awfully conservative for a 6000W inverter and again it's rarely sunny and cold here. (Southern California, near the beach)

One more thing - 2 of the strings face south and one of them faces west.

The client wants to pretty much max out the roof area even if it means some small inefficiencies.

What do you think?

mike95490

Re: String Sizing SMA 6000 and SolarWorld 175s

newenergy wrote: »

One more thing - 2 of the strings face south and one of them faces west.

Not having played with the SMA sizer, I'll assume you get "yellow" for over current/over power reasons. Since the 2 strings face different directions, they will never "peak" at the same time, so your power will be more even throughout the day, rather than a peak for 30 minutes.

newenergy

Re: String Sizing SMA 6000 and SolarWorld 175s

Hoping Solar-Guppy will chime in here as it's related to some other recent threads.

In this case is SMA software recommending an installation that might not be great?

Is the stated SMA MPPT range actually larger than they report because they want to be able to report a higher efficiency?

And yes, I am starting to quote Xantrex more than SMA, but I'd rather use one inverter and as far as I know Xantrex doesn't make a 6k inverter. Also, I'm overcoming some resistance that I had because my business partner spent a lot of time replacing Xantrex inverters that had problems turning on. They seem to have solved that problem though.

BB.

Re: String Sizing SMA 6000 and SolarWorld 175s

I think what SG is referring to is a section of the:

http://www.sma-america.com/solar-technology/solar-design-tools/index.html

String Sizing Program's output... If you go in and fill the required information... Say:

SB 6000 US (208/240)
Solar World
SW 175 Poly

"Get Sizes" at bottom of page...
"Predict Outputs" at bottom of page...

And take the rest of the defaults--

You get a very detailed results page that seems to not always give useful information... It does give spreadsheet results for:

1) Estimated PV Array Maximum Open Circuit Voltage vs. Low Temperature (°C/°F)
2) Estimated PV Array Minimum Open Circuit Voltage vs. High Temperature (°C/°F)

3) Estimated PV Array Minimum Peak Power Voltage vs. High Temperature (°C/°F)
4) Estimated Inverter Maximum Output Power vs. High Temperature (°C/°F)

5) Estimated Inverter Maximum Output Power vs. Low Temperature (°C/°F)
6) Estimated PV Array Maximum Output Power vs. High Temperature (°C/°F)

The original poster is using SW 175 panels (don't know what type) as 3x10 strings (if I recall correctly)... Going through the charts:

Voc 529 @ 32F "yellow"
Voc 401 @ 104F "green"
Vmp 327 @ 104F "green"
Pmax 4550 @ 104F "green" inverter power max
Pmax 5322 @ 32F "yellow" inverter power max

The Xantrex sizer has similar voltages (Vmp 309 @ 104F--but that may because I don't have the correct SW 175 model)... And, for Xantrex, it shows a CEC rating of 5127 watts.

Looks like the two are pretty close...

-Bill

newenergy

Re: String Sizing SMA 6000 and SolarWorld 175s

I meant strings of 11 SolarWorld 175 monos, which now that I look at it again it is looking pretty lousy.

argh

I think I can do two arrays

One with one string of 12 Evergreen 195s on a Xantrex 2.8
the other with two strings of 9 Evergreen 195s on a Xantrex 3.3

and get 75 more watts DC and it'll end up being about $2000 less. I'll also be able to put the string with a different orientation on its own inverter.

I'm trying to do too many things at once

The strings of 9 are pretty low voltage, but the Xantrex sizer doesn't mind them. Average high ambient temperature is only 79 deg F.

mike95490

Re: String Sizing SMA 6000 and SolarWorld 175s

newenergy wrote: »

One more thing - 2 of the strings face south and one of them faces west.

Since the strings face different directions, the system PEAK power will be less, and the sizer can't factor that in. You may be able to get along with a GT5 for 360 days of the year, and the other days, it will power limit itself.

what you can discover, and indeed, you need to verify (I'm also SoCal Beach area) is we DO get frost once or twice a year, and you should set 30F as the low end, just to make sure the inverter does not see an overvoltage condition as it is starting up on a cold AM.

Also, make sure on a hot day, we do (even at the beach) hit mid 90's once in a while, and depending on the roof surface and spacing, you will have voltage "droop" and you don't want to get below the minimum MPPT voltage of the inverter. Some gentleman in Mass. is having that kind of trouble, summer hit, and he's below MPPT, and getting less than 50% of his array harvest. He's got to install more panels to each of his nearly useless strings, to get the inverter running in the heat.

Cold Mornings, Max voltage Warning
Hot days, Min MPPT voltage
example -
My winter start up voltage is 345V OC for about an hour after sunrise
My summer heat low voltage is (325V start up) 278V droop at hot part of a 88F day

For a 20F thermal swing (air temp), I see a 47V difference.
Panels on a medium grey asphalt shingle roof with 6" air gap.

newenergy

Re: String Sizing SMA 6000 and SolarWorld 175s

Yeah, I've been following the story in Massachusetts.

The 11 SW175s don't exceed the Xantrex 5.0s 550V until 5 deg F, which is well below the record low here. And yeah, it will basically never exceed 5000W AC at least not by much, so that's a possibility. The efficiency charts of inveters seem to mostly go down when you increase the power though.

mike95490

Re: String Sizing SMA 6000 and SolarWorld 175s

I've got a 4.5KW array, at a less than optimal angle, west facing. Last year, I only hit the GT3.8 power limits for a couple of days, and only for short times. Seems like as the angle "improves" so does the heating, and output droops, keeping the inverter mostly happy, except for the coldest/breeziest sunny days in May, June & July
a 5KW inverter may do the trick for you. Maybe do a study for the West panels, and then for the south, and see what the peak overlap is.

Solar Guppy

Re: String Sizing SMA 6000 and SolarWorld 175s

Since your arrays are mixed, as Mike points out you will never get the "peak" power off all three at the same time.

A Xantrex GT5.0 should be fine, just size the arrays as equal lenght strings of panels.

I have 30 , ES-170's on My GT5.0, peak AC is about 4.4kW in cold weather.

For your install, I think you could push it to three strings of ES-195's ( 11 each sting ) and be fine. Since all three arrays can never be at peak, you will have a nice fat power curve and produce 4kw+ for 6+ hours a day in the summer

newenergy

Re: String Sizing SMA 6000 and SolarWorld 175s

Solar Guppy wrote: »

Since your arrays are mixed, as Mike points out you will never get the "peak" power off all three at the same time.

A Xantrex GT5.0 should be fine, just size the arrays as equal lenght strings of panels.

I have 30 , ES-170's on My GT5.0, peak AC is about 4.4kW in cold weather.

For your install, I think you could push it to three strings of ES-195's ( 11 each sting ) and be fine. Since all three arrays can never be at peak, you will have a nice fat power curve and produce 4kw+ for 6+ hours a day in the summer

I can't really go with 33 ES-195s [see below], but.....

195s have a Isc = 8.15A if you have 3 strings you have 24.45A Isc. The NEC has a multiplication factor of 1.25 for the current for days with higher than 1000w/m2 irradiance. If you multiply by 1.25 you have slightly over 30A, which is well over the 22A max input current.

I'm not just trying to nitpick - I just want to understand as much as possible about how to design PV systems.

Is it not appropriate to use the short circuit current there? Even if that's true, Imp = 7.2 and if you multiply by 3 and then 1.25 you get 27A. Does it not make sense to use the Imp with the 1.25 factor since the inverter will regulate the current to Imp even when the irradiance is higher? But then that Imp of 7.2 is based on 1000w/m2.

Is the max input current per terminal? That doesn't seem likely and Xantrex support says it's not.

Xantrex support said to use the Isc, but didn't seem to know whether or not to use the 1.25 factor and didn't seem totally confident on the whole so I thought I'd check here.

_____
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below = not important, just read if you're curious

In this case I can't use 33 Evergreens because they are a little to wide. That lead me to the 33 SolarWorlds. I could do 30 Evergreens, but they won't string right on one inverter, but I could use a Xantrex 2.8 and 3.3, but there isn't a ton of room for inverters.

Solar Guppy

Re: String Sizing SMA 6000 and SolarWorld 175s

The input available current is meaningless, The GT inverter simply limits to the DC wattage limit of the inverter, which is about 5350 watts DC for the GT5.0.

Also, for your calculations, all three string cannot be at maximum amps as only two of the three can be perpendicular to the sun, so the third array is off at least 90 degrees from peak ( the difference of the direction the stings point )

From a performance standpoint, you will do a bit better with the two inverters as the 3 arrays will be somewhat different for vmp based on the sun angle and tempatures, so I'd say a GT2.5 & a GT3.3 would perform the best and allow the best options for panels ... If you can stick with the Evergreens, they will provide more harvest than the other panels you have mentioned

newenergy

Re: String Sizing SMA 6000 and SolarWorld 175s

Thanks for your help guys.