Multiple Sub-arrays vs one big array

Hi

I am new to SAM. I am using the SAM for system analysis of utility scale PV farms for sustainable energy class. I have noticed that for a given PV system design that designing WITH the sub-arrays option on ALWAYS results in significantly better system performance. Better performance means ( Annual Energy Production KWh, capacity, and LCOE.) Somewhat puzzled by this observation. Perhaps I am missing a key fact or understanding. Has anyone noticed this? Is there something I am missing?

Carl

Dear Carl,

Can you explain more what you mean by "with the sub-arrays option on?" What two options are you comparing?

Best regards,
Paul.

Paul

Thanks for the reply..."Options" is Poor choice of words by me. Essentially, in the new beta version of SAM, on the system design page, you specify if you want to enable sub-arrays, where each sub-array is a portion of the total array size. Sub-array 1 is always enabled. The others have to be clicked on, and the data fields populated.
So, if I start with just 1 big array (sub-array 1 enabled) with 1-axis tracking I will get summary results like this..

Metric Value
Annual Energy 1,039,668 kWh
Capacity Factor 7.4%
First Year kWhAC/kWDC 651
Performance Factor 0.84%
PPA Price (Year 1) 22.01 ¢/kWh
PPA Price Escalation 1.00 %
LPPA Price (Nominal) 23.79 ¢kWh
LCOE (Nominal) 16.14 ¢/kWh
NPV $157,390
IRR 11.00 %
IRR Year 20
End of project IRR 12.85 %
Project Cost $2,924,944
Debt $1,849,305
Equity $1,075,639
Debt Fraction 63.23 %

If I enable sub-arrays 2, 3, and 4 and divide the modules per array relatively evenly, 1-axis tracking for all sub-arrays, the summary results are significantly better:

Metric Value
Annual Energy 2,342,315 kWh
Capacity Factor 16.7%
First Year kWhAC/kWDC 1,466
Performance Factor 0.87%
PPA Price (Year 1) 9.77 ¢/kWh
PPA Price Escalation 1.00 %
LPPA Price (Nominal) 10.56 ¢kWh
LCOE (Nominal) 7.16 ¢/kWh
NPV $157,390
IRR 11.00 %
IRR Year 20
End of project IRR 12.85 %
Project Cost $2,924,944
Debt $1,849,305
Equity $1,075,639
Debt Fraction 63.23 %

So, based on the big differences above (sub-arrays or not sub-arrays) I think I am missing something important.

The nameplate of the plant is 1.5MW. Module type is Sunpower 435NE-WHT(435Wdc). Inverter is Power-One Ultra 750 (750KWac.)

Carl

Hi Carl,
I would guess that the two cases are not identical (aside from the number of subarrays). To check that, you can use SAM's input browser to list variables in all cases in your file, and filter them by variables that have different values or the same values. The input browser is on the SAM menu (click the icon at the top left corner of the SAM window.)
Here's a file with two cases, one with a single subarray, and the other with four. Both cases generate the same results:
pv_single_vs_multiple_subarrays.sam
Best regards,

Paul.