Remember a 80ah lithium can be run down to below 10% giving 70ah usable. You would need a 140ah lead for the equivalant power (based on 50% discharge max) and a lithium should last 3-5 times as long as a lead. You need to factor this in when working out cost over the term.
But 1st you need to work out how much power you need per day before anything
Fridge, kettle, charging, TV etc. 12v x W = ah.
Then how many days you need off grid power for.
Then when will you use the van most? Spring/Summer only would only need a smaller solar panel than if you wanted all year round use.
Me? I have an 80ah lithium that powers a fridge, lights, kettle, diesel heater and charging which see's me right for 2 days with no solar. I also have 100w suitcasae solar that can add 30ah back during the summer. Very rare I stay any one place more than 2 days so a couple of hours driving can put back another 60ah.
So you see. It all depends on your usage and habits before you can even consider what you'll actaully need to spend.
