solar panel VMP and IMP

 VMP = voltage at maximum output
IMP = amperage at maximum output.

The VMP of most 12V nominal panels seems to be in the range of 16.9 to 17.6
See http://wholesalesolar.com/solar-panels.html  for links to downloadable
data sheets.

However, I have a 100 watt panel made by ICP, http://www.icpglobal.com , that
rates the panel at 100 watts output max, at VMP = 15volts, 6.7 amps. This is
a polycrystalline panel with 36 cells.

ICP Global is a packager; they don't make cells. The VMP of 15V is lower
than the spec for any 12V panel from any other source.

Are they derating the panel, or are they using a cell manufacturer with an
unusually low VMP ?

  That's the number with their charge controller .. these are packaged deals

All mulit/poly crystalline cells are pretty much the same , as long as it's
the same number of cells (36 for a 12v panel) the mpp point will be
16.9-17.2 volts at standard conditions (25C , 1000 watt/meter/sq irradiance
, 1 meter second wind)