Power is absolutely necessary. We like our computers and refrigerated food among other things. Living in Colorado makes solar a no-brainer with the 250ish sunny days we get per year, not to mention it is silent, stealthy, and reliable. In the future, when we’re out of debt and able to travel, we may end up in places with fewer sunny days, but hopefully it will still be a worthwhile investment. We know from past experience with solar on both of our previous truck campers that we want the most power we can get, but somewhere around 250 watts is just about right for us.
We ended up getting two 135 watt panels for a total of 270 watts. After assuming an 80% efficiency, we should be expecting about 215 watts of real output. If we need even more power, we have a pair of 30 watt portable solar panels that can be quickly deployed, boosting our total theoretical output to 330 watts, and the expected output to about 265 watts, but these will only be used when we don’t have to urban camp.