Solar and charge rates

[Tiny]

I recently purchased a motorhome that I intend to take touring for a few years. It is well set up with solar/house batteries, genset, Phoenix 3000VA inverter which also covers the charge side with the genset or shore power. From what I can tell the house batteries are 4 x 120Ah gel, currently trickle charged by 2 x 80 panels.

House batterys run lighting and a 180ltr (approx) upright fridge/freezer. A/C and 240v appliances will only be run with shore power or genset and the occasional use of microwave etc off inverter.

Currently I'm told and it appears to be correct the fridge runs indefinitely off the batteries/solar while sitting but I want to put my 40ltr engel underneath as a deep freeze and want to comfortable run lights, fridges and basics at nat parks without the use of the genset. This would realistically be a few days only at a time, house can be fully charged prior.

I know it's really how long is a piece of string question BUT assuming location gives panels output around half of the max and given the usage above how much should I be looking to expand the battery and solar banks? There is ample room for say 2 x 250w panels and can make room for batteries with no real hassles. I would probably look at diverting 1 of the 80w panels to the primary/bus battery's as the dunny runs of them

Thoughts?
Ta
Tiny

[-Scott-]

Thoughts:

I hope it's a 4x4 motorhome.

Ignoring the existing fridge, as I have NFI what it may or may not draw.

4 x 120Ah = 480Ah of storage. For longevity, you should try not to use more than 240Ah before recharging.

If used sensibly, I work on 24Ah/day for a 40l Engel, but have NFI how much a busload of DC lighting will consume. Probably not more than "two Engels" (as a new unit of electrical measure), so a fully charged battery bank should keep you going for three days without input - excluding your existing fridge.

If you want solar panels to compensate for your "three Engels" of load, you need 72Ah/day. Generally, placed in full sun at an optimal (fixed) angle, panels can average 5 hours of full output each day (will generate for longer, but not at full output the whole time - 5 hours/day is a "rule of thumb").

I presume your solar panels will be fixed to the roof, and I don't really know what this does to the output. Say 60% to keep nice round numbers? So you might get 3 hours equivalent full output each day, if you don't park in the shade. So you need panels to produce 24A at 12V, or 288W nominal. 2x250W with a decent regulator should go a long way to help you reach your goal.

Keep us informed on your progress - I'd like to hear what you find from professionals, and how your system works on the road.

[Tiny]

Thanks mate, I'll try and get a bit more data over the weekend and I'll put the question to the "experts"
We intend to document and blog the saga as we go so will update here also. The plan is we will be living and touring in the bus for at least several years and I want it pretty well sorted before we leave, we have around 5 months to do that :o