Two Modules Give Wildly Different Power Outputs For the Same System Size

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niccolo
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09 Jan 2014 13:20 #2069 by niccolo

Two Modules Give Wildly Different Power Outputs For the Same System Size was created by niccolo

Hello Everyone. I am having a bit of an issue. When modeling my 240 MW system in a given location using one type of modules (sun power) the output is one value (= 0.9* full sun hours * system size). However with another module (Renesola) the output is much lower (= 0.3 * full sun hours * system size) How can this be? Inverter is the same, location is the same, etc.

Any help would be greatly appreciated.

Thank you

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Paul Gilman

09 Jan 2014 18:41 #2070 by Paul Gilman

Replied by Paul Gilman on topic Two Modules Give Wildly Different Power Outputs For the Same System Size

Dear Niccolo,

The SunPower and Renesola modules have different maximum power point voltage and current ratings, so depending on the inverter you choose, SAM may be sizing the systems differently (assuming you are using the "Specify desired array size" option on the Flat Plate PV model's Array page.)

I've attached a SAM file to your original post with two cases, one is for a 240 MW system with SunPower 305 W modules, and the other is for a 240 MW system with Renesola 305 W modules. Both use the same 333 kW inverter. In both cases, the system performance factor is 0.82, and the total annual output is about 450 million kWh.

Best regards,
Paul.

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niccolo
Topic Author

13 Jan 2014 16:10 #2071 by niccolo

Replied by niccolo on topic Two Modules Give Wildly Different Power Outputs For the Same System Size

Thank you Paul. Using your inverter i was able to get more reasonable results out of my model. Sounds like it was just a "bad-match" between panel and inverter to give such a low performance factor. Is there a way to go about determining which inverters play best with which panels. Were would the source of this mismatch loss be in the calculation?

Thanks again for the help.

-Niccolo

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Paul Gilman

13 Jan 2014 16:33 #2072 by Paul Gilman

Replied by Paul Gilman on topic Two Modules Give Wildly Different Power Outputs For the Same System Size

Dear Niccolo,

It seems likely that in your case you chose an inverter that was too small for the array, and that caused the system output to be low compared to the array's capacity. During periods when the array's output is greater than the inverter's rated DC capacity, the inverter clips its output to the inverter rated AC capacity. You should be able to see this in the hourly results.

Another clue would be the DC to AC ratio that SAM displays in the sizing messages box on the Array page. If the ratio is much more than about 1.1, then it is likely that the inverter is too small to convert the array's DC output during hours of peak sunshine.

Best regards,
Paul.

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