Anyone else struggling to keep a 100Ah lithium topped up on cloudy days with just 200W of roof solar?

Mate, 200W trying to fill a 100Ah LiFePO4 on a British "summer" day is basically a polite suggestion rather than actual charging — welcome to the club nobody wanted to join.

I ran a similar setup for about eight months before I caved and bolted another 175W panel on the roof (Renogy, nothing fancy), and the difference was genuinely embarrassing in hindsight. Even on a proper grey Norfolk drizzle-fest I'm pulling something useful rather than watching my Victron BMV slowly tick downward like a countdown to misery.

Few things worth checking before you throw money at more panels though:

• What's your actual consumption? 100Ah sounds loads until you've got a compressor fridge running 24/7
• MPPT or PWM controller? PWM in low light is basically robbery
• Panel orientation — even a 10° tilt adjustment made a noticeable difference for me in winter sun angles

The real villain here is the UK's insistence on being overcast roughly 340 days a year. My Fogstar 100Ah cells are brilliant but they can't magic watts out of cloud cover, sadly.

Have you considered a small secondary charging source — shore power hookups, a B2B from the vehicle alternator, even a little wind turbine if you park somewhere exposed? Belt and braces is basically the only sane strategy on this island.

What's your current controller setup? That'd help narrow down whether it's a panel problem or a system problem.

@BrookLover — boat life taught me this lesson the hard way.

200W sounds generous until you're anchored somewhere in the Scottish west coast in July, watching the Victron MPPT log eleven watts at noon because the sky's basically a grey duvet.

The maths only works on the brochure. Real UK generation is probably 40–60% of rated output averaged across the season, and that's being optimistic.

What actually saved my sanity wasn't more panels — it was shrinking the loads. Swapped to a 12V compressor fridge, ruthlessly audited everything drawing phantom current overnight. Suddenly that 200W started keeping pace.

More panels are obviously the real fix, but if roof space is constrained (van life struggles are real), attack consumption first. You'll be surprised how much headroom appears.

@BrookLover @FZ_Builds — narrowboat here, so I feel this in my bones.

The maths look fine on paper — 200W peak should cover a 100Ah bank reasonably. Reality is you're lucky to see 120W average on a decent UK summer day, nevermind overcast. Factor in the battery only wanting to accept bulk charge rate properly when it's below ~80% SoC, and you're basically crawling the last 20% anyway.

What actually helped me more than adding panels was fitting a Victron SmartSolar and properly profiling the charge curve. Was losing a surprising amount just to a badly configured MPP tracker before.

That said — if you're genuinely cloud-bound for multiple days, there's no substitute for either shore power hookup or a decent DC-DC charger off the vehicle alternator when you're moving.

@BrookLover my garden office runs a similar numbers game and I've basically accepted that British "peak sun hours" is just a myth we tell ourselves to feel better — like thinking the M25 will be clear on a Tuesday.

Slapping a Victron SmartSolar on mine at least meant I stopped wasting what little light I do get, but honestly the real fix was a second panel rather than a fancier controller — 200W of hopeful thinking becomes 400W of mild optimism, which is just about enough to survive a grey Yorkshire fortnight.