Advice on ultra small project

[krby]

I've got an idea for a self-contained solar project. I've got gear I would like to put in a weatherproof box with a small solar panel, a small battery, and a charge controller.
The load is 5-6W max at 5V DC, running 24.7 Locations would be Northern California, likely on a flat roof. Ideally the panel would be no more than about 2ft x 2ft. If this even possible? How many days of no-sun should I plan for? I could get buy on a 6V battery, but probably would use 12V just to make finding the gear easier. Do really small (<25W) charge controllers exist?

 

[gnubie]

It sure is possible. I've done something similar myself as mentioned in other threads about the same sort of project. In my case it was to get mobile (cell) internet access on a hill to a house in a difficult location via wifi.

Low power PMW lead acid charger boards can be bought off ebay, there's even an MPPT one (if you can believe the ad). 2' x 2' would get you an easy 50 watts (peak) which is far over your load that you don't need to worry about efficiency really. Clouding would knock production around but given the panel produces so much power unless you have doom end of the world level clouding it's still going to produce a significant amount of power over a day compared to the load. A 7.5ah 12v battery will hold your load up for about 9 hours (50% discharge) with no sun at all so maybe consider the equiv of 14ah of storage.

If using 12v battery the load can be hung off a cheap ebay buck board for about $2.