powering cm500 with solar cells

> I need to power several cm500 cable modems with solar power. [...]

   "several"?  One location, or multiple?

> [...] Can someone provide some definitive information on what kind of
> solar cell I need and where I might find them?

   With that requirements specification?  I doubt it.

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual.  Read.  Look for "Technical
Specifications" and "power"?

   That would give you an upper bound on the modem's power requirement.

   You don't need a "solar cell".  You need a solar panel, with a
suitable voltage regulator, and enough capacity to handle the required
load, under the solar lighting (and other environmental) conditions to
be expected.  And some kind of storage battery might be helpful, too.

   In other words, some actual engineering might be required.

   And the non-psychics here might not know where you are.