It isn’t a simple answer to be honest. There are a ton of factors to think about. Anything from your environment (sun available, temps you have to deal with etc), device usage, theoretical future power upgrades etc. I know that in the Four Wheel Camper, I used on average about 40 amp hours (AH) a day with fans running and fridge working. That included lights at night and stuff like that. Given that I was moving to the van, with about the same usage, adding in more charging via inverter, I stepped it up a bit on the capacity. The big efficiency was making sure all my battery chargers were on 12v. You can get replacement chargers from amazon for your cameras and other items that use cigarette lighters to charge them (for example), thus eliminating the need for 110 usage, GREATLY reducing power consumption. By making that switch alone, I save about 20 AH a day in power. Just alone, it isn’t that much, but when you add in other things, like bluetooth speakers, phones, ipads, computers, fans etc, it all adds up, and it all helps out.
So, That being said. The list of items I used at this point, to power my Sprinter:
3x Renogy 100watt Panels – http://amzn.to/2GtENtk
Solar Gland – http://amzn.to/2padWuK
Extension Cables – http://amzn.to/2tOsgho
Solar Splitters – http://amzn.to/2FQ9P0x
These were mounted using the factory rails, and 2×2″ aluminum angle that I drilled to work.
200 Amp hour AGM battery – http://amzn.to/2FWOaE5
Victron 100/30 MPPT Charger – http://amzn.to/2FIPmaG
Victron Battery Monitor – http://amzn.to/2peeFdE
Marine Battery Charger for shore power – http://amzn.to/2tNaZF9
Blue Sea Fuse Panel – http://amzn.to/2GteNy9
Exterior 110v plug – http://amzn.to/2FQMgoi
110V Splitter (One to charger, one to power strip) – http://amzn.to/2pctAVN
Blue Sea Battery Switch (disconnect vehicle aux battery from house battery to enable charging/not charging) – http://amzn.to/2FVGwti
Blue Sea 6 switch panel – http://amzn.to/2FTYVa8
Blue Sea 4 switch panel – http://amzn.to/2FHo6Jx
12v plugs – http://amzn.to/2tSiryG
USB plugs – http://amzn.to/2FAZkyX
16ga wiring for lights and USB – http://amzn.to/2FJz4OL
12ga for everything else – http://amzn.to/2FKEA3t
4ga wire for large connections – http://amzn.to/2FL4yUQ
2000 Watt Modified wave Inverter with remote – http://amzn.to/2peOpzE
For the most part it is pretty straightforward. The only slightly odd thing is the Overhead lights and water pump, which both run off two switches. One in the front and one in the rear in order to have them to be turned on from either location. Basically just two wires ran from the pump/light to each switch.
All these products were chosen because of personal experience coupled with a few good friends in the industry. So far, zero issues and awesome power with no regrets. Going with decent gear makes all the difference for things just working!