Off grid use

A further consideration - location. You don’t say what you’re intentions are for off-grid use, but you’ll get a lot more solar for your bucks if you’re travelling in southern Europe, apparently up to 3x better than typical UK. Even in the UK position can make a big difference. I understand there can be 30% difference in solar gain between North of Scotland and where I live on South Coast of Cornwall same day/same conditions.

I used to have a VW T5 with 100W solar panel, Victron MPPT solar controller, 90ah gel battery and a 12V Dometic compressor fridge.  In the England/Wales from about April until September I could easily go away for a weekend (5 days or more if the sun was out) without EHU.  I didn’t have a TV so it was just power for the fridge, lights, water pump and diesel heater.

As the T5 had a pop up roof, I used to park so the solar panel was facing south as far as possible.  You get more power from the panel on a pop up roof than having it flat.

If you are having problems, I’d check your fridge is wired directly to the leisure battery with big diameter cable (the biggest that will fit) and have the shortest cable run possible.  Don’t put a switch in the cable (just a fuse at the battery end).

I’d also check your solar controller.  If it’s a cheap PWM then bin it for a quality MPPT controller.

I think that if you want to use your fridge off grid for more than a few hours, then a 3way absorption fridge is a must, running on gas. However, absorption fridges rarely provide as much cooling as compressors, which can lead to marginal efficiency in hot weather. Ours struggles to go below 8deg C, and it really needs to cool to 5deg C. You’ll notice the considerable increase in gas consumption too. Even with extra solar power, fridges running on 12V are really only meant to do so for holding an already cold fridge’s temperature. That’s more of an absorption fridge problem than it is for compressors.

Another problem which applies to batteries is the gap between the rated power and reality. In many instances their capacity can be as little as half the advertised figure. A leisure battery supplying a low demand will deliver more energy before it needs recharging, than one which is the subject of higher loads. Worse still is a memory effect which reduces capacity after being run down to less than half. Smart chargers can restore performance, but a solar panel doesn’t have that capability.

We do use our caravan off grid with 110W of solar power which can’t keep up in dull weather, so we have a backup battery to swap in when required. We’ve also tapped into the car’s split charge relay output so that the backup battery can recharge when driving without the caravan. Substantial gas consumption is catered for with refillable Safefill bottles because Autogas is less than half the price of Calor. As you have a Motorhome, simply driving or running the engine will recharge your batteries.

Theres as much art as science in going off grid.