Mike
Thinking aloud..........My 13.5mm2 'umbilical cord' was originally to have been the solar to battery cable for what then were portable panels & the determining factors on the length of that cable were cable weight & cost as well as minimising voltage drop. The panels are now much closer to the controller but still 13.5mm2. Less concern re voltage drop in battery to load connection (so long as the load works) & now battery health is not impacted by it. (Reduction in average battery SoC is negligible). A longer portable solar/battery cable was too cumbersome for carrying around & packing away. So now with our car top solar & car mounted batteries our camper sites under trees generally need to be within 10 metres of sun access for at least a few hours of the day unless moving on within the following day or two.

I guess if your 800w of 200w panels can give you around 7 amps per panel then they must be 24v. As you say you could connect those panels in series to increase voltage. I don't understand why you haven't done so given your camping preferences & by the sound of it resorting to generator use more often than you like to.

I have never yet made the switch from 12v to higher voltage panels/MPPT controllers despite my controller being a reasonable MPPT one. Today if I were setting up, with all the ex house panels of higher voltage around & cheap I think it would be a no brainer. Maybe like you I just live with what I have? The difference perhaps being however that I generally place a high priority upon choosing a camp with reasonable access to sun. Your priorities sound different.

Whilst MPPT will help by boosting what voltage reaches it if need be, wouldn't the boosting essentially be a load (?) & if so wouldn't there be a vicious circle of diminishing returns with more boost resulting in more voltage drop resulting in more boost etc etc? If so reducing relative losses as much as possible by both increasing solar voltage & cable sizing would seem to be sensible & achievable without huge cost, particularly as your skillsets would seem to make it a fairly simple DIY project.

I understand your thinking about 'something is better than nothing' in regard to cable length & what it provides but not why you might even muse about 1.5mm2 extension cable, nor really why you wouldn't search out sites you like that are more sun accessible.

Disclaimer - I had to look up the IR reference introduced by Dorian but maths was never a strong point of mine, but I note the analogies to water flow/pressure & restriction in your link, which is what I was trying to explain. I may be wrong but my sense is that even though it only an analogy it works quite well in comprehending what works & what doesn't even if not strictly accurate? I'm not sure if when introduced as a 'musing' whether the 25m 240v cable it was done so with a bit of tongue in cheek humour & something I should just have smiled at.

Edit: I just noted your comment about series connecting panels making them more susceptible to shade reduction. Not come across that before. What a bummer!

-- Edited by Cuppa on Saturday 17th of December 2022 09:27:43 PM