RV Installation

Had a similar headache when I sorted the solar on my motorhome last year. Came with a basic 175W panel and a fairly generic PWM controller — first thing I did was swap it out for a Victron SmartSolar MPPT 100/20, which made an immediate difference.

The wiring side is where it gets fiddly though. Previous owner had run the cabling through the roof entry gland without proper fusing on the PV side, which is a real concern. A lot of factory installs cut corners here.

Current setup:

• 175W panel on the roof
• Victron SmartSolar 100/20
• 100Ah Fogstar Drift LiFePO4
• Properly fused at the panel end and at the controller

The inline fuse question comes up a lot — worth noting that for UK/EU installations you technically need overcurrent protection as close to the source as possible. Most people stick a ANL fuse or blade fuse right at the panel combiner or first connection point before the cable runs any distance through the vehicle. The idea being if there's a short in that long cable run, you want something to blow before it becomes a fire risk.

What controller are you running and what's your battery situation? If you're looking to add a second panel down the line, it's worth checking your MPPT's voltage/current limits before you commit to anything.

Also — are you planning to integrate any EV charging into this at all? That's my next project and the power balance gets interesting quickly with a small roof setup.

Curious what others have done with their motorhome installs regarding cable routing and fusing.

@Mark1978 same boat with my shepherd's hut build — ditched the PWM straight away, what a difference.

One thing worth flagging: check your cable runs before anything else. I wasted a week troubleshooting poor harvest before realising I had undersized cable over a longish run from the roof. Voltage drop was killing my numbers.

Also if you're upgrading the panel at the same time, worth measuring actual roof space carefully — I assumed I had room for a second 175W and had to reorder a slimmer 160W instead. Lesson learned the hard way.

What battery setup are you running? If it's still the original lead-acid that came with it, the MPPT will help but you'll hit a ceiling pretty quick.

Good shout from both of you on ditching PWM early. One thing worth adding for anyone running a van conversion or narrowboat setup — the MPPT efficiency gains are most pronounced in low-light conditions, which in the UK basically means October through March, i.e. when you actually need every watt you can squeeze.

On my narrowboat I'm running a Victron SmartSolar 100/30 paired with a couple of Fogstar 200Ah LiFePO4 batteries, and the difference in harvest on a grey February day versus what the old PWM was managing is genuinely stark — we're talking 15-20% more usable charge regularly.

Also worth checking your cable runs and connector quality when upgrading — a decent MPPT paired with undersized cable is just leaving money on the table. MC4 connections especially; the cheap ones are notorious for voltage drop and heat buildup.

Something I'd add to what @Mark1978 and @AnneWatson have already covered — when you're sizing your MPPT for a motorhome specifically, don't just match it to your current panel wattage. I made that mistake initially, bought a 75/15 thinking it was plenty for my 200W setup, then added a second panel six months later and had to replace the controller entirely.

The Victron 100/20 costs perhaps £30 more at the point of purchase but gives you genuine headroom for expansion. I now run 400W through mine without any issue whatsoever.

Also worth being precise about your Voc figures in cold conditions — British winters will push your open-circuit voltage noticeably higher than the panel's rated spec. Run the numbers through Victron's MPPT calculator before you commit to anything.

Good points all round, but nobody's mentioned temperature derating yet. If you're mounting panels flat on a roof — which most motorhome installs end up being — you're losing meaningful output on hot days. MPPT helps recover what it can, but you're still fighting physics.

On my static caravan setup I tilted at 15° minimum, purely for airflow underneath. Not always practical on a moving vehicle, I get that, but worth knowing why your numbers might not match the spec sheet come July.

Also worth flagging: Victron's MPPT calculator on their website is genuinely useful for checking whether your panel Voc is safe in cold British winter conditions — don't skip that step, an undersized controller input rating will get damaged if Voc spikes on a cold clear morning.