Evergreen Panels listed as 18V not 24V Why?

well for the 18v crowd, essentially we know how many volts per cell, which makes for standard cells per module numbers. 
12v have 36 cells, 24v have 72 cells, and 18v serves as a catch-all for everything in between although most will have 48-54 cells.  the evergreen i believe has 108, a multiple of 54.

for outliers, like sanyo, it is important to remember that nominal is a distinction based on batteries.  most modules nowadays go to grid tie, so batteries are irrelevant.  the sanyo has no real "nominal" voltage because it was never meant for battery charging, and does not tuck in nicely to a category based on voltages or cells.  that being said you can use them for battery charging, but open format mppt controllers must be used.

if 12v modules run at 17v, then 24v modules run at 34, and 36v nominal (if they existed, or two 18v in parallel) would run at 51v, then 48v modules (or strings to make 48) would run at 68v. 

being that the sanyo runs at 55v at stc, it is above 36v nominal, but below 48.  the 42 number we put on there serves mainly as a warning to those attempting to charge 48v battery banks on a sanyo module that will only get to 55v before temp deration and likely not be successful in charging a battery bank at 48v, especially in warm climates where temps draw voltage down.  the other side is that two of those modules in series in a cold climate will come very close to destroying mppt controllers with max vdc of 150.

good questions, some folks get turned off by this stuff, but i think the more you know, the more fun the system design is, and the more options you have open to you because of that understanding.

cheers,

james
Alt-E staff