NABCEP PV Installer Resource Guide Forum
General Category => General PV Discussion => Topic started by: jen cooper on February 19, 2012, 01:46:45 PM

Hi
I'm new to the P.V. study guide forum. I will be sitting for the installers exam in March and couldn't help but notice a few (mistakes?) in the case study and the practice question section of the December 2011 5.1 version Installers Resource Guide. I would love to get some help with these, a second opinion, some clarification, corrections or a revised study guide.
Question number 8, Newark, NJ case study They are looking for a voltage drop % of less than 2. The Vnom given in the answer is from the inverter (240v) not the P.V. array: (14 modules @vmp = 413v DC).
Question number 2 in the Sample Questions They ask where the inverter should be located to maximize system efficiency, performance and to minimize wire size. The answer given is C) at the utility point of connection.... But to minimize wire size, voltage drop and maximize system efficiency you would really want make the DC wire runs as short as possible which would mean that the inverter would be located at the PV array.
Question Number 3 sample questions there is a voltage drop formula instead of an array shading diagram.
Question Number 6 sample questions Not really sure what is going on here. 90% of the annual load is 6.21 Kw and @80% system efficiency is equal to 4.96 Kw the given answer is B) 4.43kw...?
Where is question # 7?
If anyone else has had issues with the study guide or knows of any other mistakes please post. My main concern is that if the actual test is written like the example questions are, none of us have a chance of passing.
Thanks
Jen Cooper

O.k.  on question 3 study guide, its true the AC voltage drop would be greater than a DC run because of the operating voltage; lower voltage higher current...
I still don't know what is going on with question 6. Anyone have any ideas?

Here's how I did it:
(6900kwh x .90/365) / 4.8 hours (latitude 15 tilt) x 1.25 = 4.43kw
The latitude 15 comes from the fact that the roof is at 26 degrees which is 15 degrees less than the latitude of 41.53 degrees. The 1.25 factor is the reciprocal of .8. Hope this helps.