What about snow on the panels?

There's no getting away from it, snow is going to accumulate on the solar panels and enough of it can bring the solar production to zero.  Clearing the snow will help production, however may not be practical or worth it, due to the low sun hours in winter.  If the system is mounted on pitched roof (most residential roofs) clearing the snow off sloped roof mounts can be dangerous and is not recommended. If the system is mounted on a low slope roof or ground mount, that can be safely cleaned, go for it.

An off-grid system that is dependant  on the sun to charge the battery system does require the panels to be cleaned. This can be made easy by having the solar panels ground mounted. 

Be sure to check out the NAIT/City of Edmonton Reference Array System