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SunPower / PVMismatch

An explicit Python PV system IV & PV curve trace calculator which can also calculate mismatch.
http://sunpower.github.io/PVMismatch/
BSD 3-Clause "New" or "Revised" License
79 stars 30 forks source link

PR #73 breaks temperature dependance #76

Closed chetan201 closed 6 years ago

chetan201 commented 6 years ago

What's expected - (reverting back to pr #68

image

What's observed in pr #73 -

image
chetan201 commented 6 years ago

@mikofski
off the top of your head, do you know why this might be happening? Shall I revert the master to PR #68 meanwhile?

mikofski commented 6 years ago

Yes, it's because we fixed vmax at stc condition. But at -40C, -25C, and zero degrees Celsius, the cell voltage will be greater than it would at stc. So therefore vmax is not high enough.

The fix should be to use the larger of vmax at stc versus vmax at the desired cell temperature.

Reverting to #68 fixes this problem for now, but then recreates the problem where we get weird behavior when there is heavy voltage mismatch or bypass diode activation.

I'm sorry I hadn't considered temperatures lower than stc. It's uncommon to see temps this low but not impossible, eg snowy conditions.

Thanks for bringing this to my attention. Nice catch. Really useful information for me!

mikofski commented 6 years ago

Another fix idea, would be to just pick a 4th quadrant current, like -10A, and just go up to that value always. I'll try to implement one of these two approaches and put in a new PR asap. Until then, yes, I think you would be better reverting to 4943742f68a1819d258bf930d89c4b05f06b7630

sorry!