I hadn't done any electrics before this van project, but there is a wealth of information online.  I opted for a simple 12v system.  There's 180 W solar panel on the roof that charges a 115Amp hour leisure battery through a charge controller.  There is also a split charge relay system installed so that the battery charges when the vans driven.  This all powers 4 LED lights, a water pump, some LED strip lights and a shower/toilet light, with plenty of juice to spare in case we want to install anything larger in the future.  I have also added a 12v cool-box that is linked to a timer so that it comes on for a couple of hours a day in the midday sun.