# Thread: Need help using SunnyDesign software

1. Solar Potentate
Join Date
Feb 2011
Posts
736

## Need help using SunnyDesign software

http://www.sma-america.com/en_US/ser...ign-tools.html

I've only fooled around with it for a little bit, but I have a few questions, refer to screen shots below please.
The first photo shows the entire system design.
The second photo has some summary numbers and I'm wondering how I can improve the PERFORMANCE RATIO = 85.6%
Help file says:
Performance ratio
The Performance Ratio (PR) is stated as ratio between the nominal yield and the target yield of the PV
plant. It thus shows the proportion of the energy that is actually available for export to the grid after
deduction of energy loss (e.g. due to thermal losses and conduction losses ) and of energy
consumption for operation. The closer the PR value determined for a PV plant approaches 100 %, the
more efficiently the respective PV plant is operating.
I found this document too which I need to read:

The last photo has a Cable diagram that I don't understand at all.
The help file gives the following explantion of terms:
Graphic of cable distribution
The graphic should help to become orientated with cable dimensioning. The graphic
shows where the cables run in the planned PV plant and at the terminal to the power
distribution grid of the DC lines, the AC1 lines and the AC2 lines:
• "LDC" is the simple cable length from the inverter to the first PV module in the string.
• "LAC1" are the cables from the inverter to a possible sub-distribution.
• "LAC2" are the cables from a possible sub-distribution to the feed-in point.
How does the software know how long the wire run is?
How did it come up with 16 AWG?
My calculations show the following
Panel Isc=8.12Amps
Two strings = 16.24 Amps
16.24x1.25(safety factor for overload) x1.25(safety factor for excess production) = 25.4A which is 10AWG wire!!!
Thanks for any help. You're probably wondering why I am using a program if I can do the calcualtions myself? It's the first time I'm putting together a grid tie system and I just wanted to double check everything. Any help is appreciated.

Last edited by rollandelliott; June 5th, 2011 at 7:13 PDT.

2. ## Re: Need help using SunnyDesign software

The diagram shows four strings of three panels each feeding into two inverters which then couple to feed the grid. Very straightforward if a bit mystical in designations. "L" stands for "Line". DC Line, two separate AC lines - the second being the two inverter outputs coupled and connected to the grid.

There is a box that says "Single cable length per string: 47 ft" and another that says 16 AWG - these appear to be user selectable. If you want to get the efficiency ratio up, shorten the wire and/or increase the gauge size to reduce Voltage loss in the wire. There are separate tabs to select and input info regarding the AC side to calculate losses there.

Looks like quite a good tool to me.

3. Solar Potentate
Join Date
Feb 2011
Posts
736

## Re: Need help using SunnyDesign software

Your explanation is exactly correct, however....... the graphic has NOTHING to do with the system I specified which is two strings of 14 panels each. unfortunately it appears that the same graphic shows up regardless if you have 1 to 100 inverters or 4 or 400 panels.
Yes the gauge and wire length can be entered but none of the numbers at the very bottom project tab (like total cable length=188 feet) can be entered and I have no idea why the software seems to think it knows how long of a wire run I need.

Like any tool, it's only good if I know how to use it, and right now it's giving me the wrong wire size which is dangerous. I'll call up SMA on Monday and see if they can help.

4. ## Re: Need help using SunnyDesign software

Graphic just gives you an idea of what infomation they are talking about. The 188 ft is the product of 4 run's of 47 ft DC + & - wires for each string. Also, wouldn't you use 8.12 x 125% x 125% = 12.69 amp to size the DC wire run to the inverter? Keep in mind if in conduit, wire temp rating 90°C etc and conduit fill deratings to come up with your final wire guage required. My guess is you would be in the #10 or #8 wire guage after appropiate deratings for temp/in conduit/conduit fill factors. #8 will also, give you only about 0.4% drop for that length.
I downloaded the latest version good tool to guide you through design. I choose a different mfg inverter for several different reasons. Wish that I had the roof /land space to put that much panel in a single orentation array, but i don't so in the final stage my second array will be 90° from my current system on a second GT3.8 total of 7200 watts of panel with 2 x GT3.8 Inverters

Good luck with your system. sounds like it will be a good producer. One mfg design tool isn't going to give you all the information which includes many variable of your installation. Roof / Ground mount, codes of wire types, in conduit sun exposed / buried direct or in conduit, local codes etc. Most local building inspection personnel will give you guidance on what they require. It would sure be nice to have such a comprehensive design tool but I haven't found it yet, or they are very expensive to purchase.

http://www.electrician2.com/

This site has some calculators that will help for in-conduit/ and conductor fill in conduit. etc.

5. Solar Potentate
Join Date
Feb 2011
Posts
736

## Re: Need help using SunnyDesign software

Also, wouldn't you use 8.12 x 125% x 125% = 12.69 amp to size the DC wire run to the inverter?
I guess from the panels to the DC combiner box that is the right calculation.

but I have two strings of 14 panels wired in series.
The two strings are then wired in parallel @ the DC combiner box, so Amps is doubled 8.12x2 = 16.24A
10AWG wire from DC combiner box to inverter will need to be thicker to handle double amps.

Thanks for figuring out how the program comes up with that wire run length.

This ground mount is going to be about 80 feet away from the power meter. Is it better to run 75 feet of "DC wire" or "AC wire"? The AC wire is gonna have to be 8AWG (25A x 1.25safety factor)=31.25A.

So it would be cheaper to run the 10AWG "DC wire" that distance, but since I've never done it maybe there is something I'm overlooking.

6. ## Re: Need help using SunnyDesign software

It's best to have the longest runs on the highest Voltage. For grid-tie this is usually the DC side as opposed to the 240VAC inverter output.

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