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Determining low temperature that caused the inverter to go over voltage


Q:

Sean: Thanks for a great course. Two questions: I think I would like some additional training for the PV Installation Professional Certification Exam. Do you have any recommendations?
Also with the addition practice questions, I got really knotted up on questions 74 and 78. On question 78, when you state the temperature coefficient for the module, is this actually Voc x Temperature Coefficient Voc?
Again, thank you for two great classes. I look forward to meeting you in person someday, and perhaps attending hands-on training you might offer.
My best to you

A:

For 74 and 78 we have to work backwards.

We are asked to determine the cold temperature and we are given the number of modules in series, temperature coefficient Voc and the inverter maximum voltage.

We first divide the inverter voltage by the number of modules to get the cold temperature voltage.

78 has a temperature coefficient that is in mV per C, so it is a little confusing, but simple once you see it.

145mV = 0.145V

We then find out the difference between the Voc at STC and the Voc at cold temperature.

Then we will divide that difference in voltage by 0.145V to get our delta T and then figure out how far our delta T is from 25C.

1000V/20 modules = 50V per module

50V cold Voc - 44V STC Voc = 6V is the difference in voltage

6V/0.145V = 41.4 Delta T

41.4 less than 25 is -16.4C

Isn't that cool!

Sounds like you are about done with the class.

This is the best class for preparing for the NABCEP PVIP exam and I think the best thing to do is go over this material a bunch.

I also teach workshops at Intersolar US in SF in July with Bill Brooks and at Solar Power International in September (Vegas) with Bill Brooks right before the NABCEP Exam. That would be a good way for you to get a chance and heckle me from the back row!

Also, there are other classes here at HeatSpring by other instructors, such as Ryan Mayfield https://www.heatspring.com/courses/megawatt-design?aff_id=t3nlgw

I have a NABCEP PVIP Prep course here too that covers a lot of the same material as this course.

Thanks!!!

Sean White


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