Why wouldn't you buy this 45watt Solar System for $149???

One more thing: panels 100W or larger are meant to be roof-mounted, mostly people just mount it flat, with no provisions for tilt. Life is easier this way. 100W panel is a bit of pain if you want a portable tilted setup like that 45W kit. Doable, few members did this, but you might not like it in the end. Again, flat means less output, that's why I wrote that for your purposes it's better be 120W if you want it flat. You "might" make it with flat 100W if weather cooperates and if you are not running laptop too often.