The first part of the research was to see what amount of energy is consumed by the node in a normal use. For the measurements we set the high power (600mW) wifi cards which take the maximum consumption.

The average current is 0.24 A which comes to be 2.88 W powered with a 12 V source, and which leads at least to 2.88 W x 24h =  69.2 W (in a day)

With a 20 W solar panel we get to power the battery with an average of 100 W (each day) depending of the day (from 120 W (day) in sunny days to 60 W (day) in cloudy ones).

The battery used is also important due to the fact that in cloudy days it has to support at least 10 W extra power during the hours there is not enough light from then sun to get the necessary 69 W. For our tests we used a cheap 65 Ah battery which was more than enough to get over this days and to get our node always running.