Parametric Analysis on PV System Size or DC-AC Ratio

Hi Craig,

Would you mind attaching a copy of the .sam file you used to generate these results so I can investigate?

Best regards,
Paul.

Hi Craig,

Thanks for sharing your file.

As described in the "PV Sizing and Configuration" topic of Help (under Photovoltaic Systems in the table of contents), the sizing calculator works best for arrays with large nameplate capacities. The best way to have full control over the system size is to specify the number of modules per string and strings in parallel and then use the number of modules for the parametric input.

First some definitions:

Rdcac = Pdc / Pac
Nmodules = Nstrings * Nmodulesperstring

Given the 55.5 kWac inverter and 0.343 kWdc module in your .sam file:

Pdc = Nmodules * 0.343 kWdc
Pac = 55.5 kWac

We'll set number of modules per string to 6 to stay within the inverter's voltage limits. (We could also use 7 modules per string, which brings the string nominal Voc closer to the MPPT maximum of 480 VDC.):

Nmodules = Nstrings * 6

Putting all of that together to calculate the number of strings required for a given DC/AC ratio:

Rdcac = Nstrings * 6 * 0.343 / 55.5

or

Nstrings = Rdcac / 0.037

Now:
1.1 / 0.0371 = 29.6 (29 or 30 modules for DC/AC ratio = 1.1)
1.2 / 0.0371 = 32.3 (32 or 33 modules)
1.3 / 0.0371 = 35.0
...

Now if you clear the Estimate Subarray 1 configuration check box, set Modules per string in subarray to 6 (or 7), and set up your parametric runs on Number of parallel strings, you can see how changing the DC array size affects the annual energy, NPV, and payback period. You can show the nameplate capacity in the results and divide that by the inverter AC capacity to calculate the DC/AC ratio. (Use the Export menu to export the table to Excel or CSV.)

Attached is a modified version of your file that I used to generate these results:



Best regards,
Paul.