Question about new solar configuration on board

So here's where I'm at — I've been living aboard my narrowboat for about three years now, and the solar setup I inherited when I bought her is starting to show its age. We're talking a cobbled-together system with two 110Ah lead-acid leisure batteries (both getting on a bit) and a fairly basic PWM controller that predates most of the kit I'd recommend to anyone today.

I'm seriously considering a full overhaul before next winter, and I'd love some input from people who've been through similar.

My rough plan:

• 2x 200W panels on the roof (limited by the cratch cover situation)
• Victron SmartSolar MPPT controller — probably the 100/30
• 2x 100Ah lithium (looking at Fogstar Drift as the budget option, open to alternatives)

A few things I'm unsure about:

1. Is the 100/30 going to be sufficient for 400W of panels, or should I be sizing up to the 100/50 now rather than later?
2. With lithium, do I need to completely rethink my existing 12V wiring setup, or is it mostly the charging parameters that change?
3. Anyone running this sort of setup on a narrowboat in the UK and finding it adequate through the darker months? I'm moored on the Kennet & Avon so we do get some properly grim grey weeks in November.

I'm not a complete novice but I'm no sparky either — I've watched enough Victron webinars to be dangerous. Would really appreciate hearing from anyone who's done a lead-to-lithium transition on a boat specifically.

Hey @Midge, welcome to the forum! Three years liveaboard is enough time to really understand what your actual power demands are, which puts you in a great position for planning a proper upgrade.

One thing worth mentioning that catches a lot of boaters out — narrowboat installations have some quirks compared to static off-grid setups. Shading from bridges and trees hits you constantly when you're moving, so panel placement and whether you go with MPPT controllers really matters more than on a fixed installation.

Could you share a rough idea of your daily consumption and what battery bank you're currently running? Makes it much easier to give useful suggestions rather than just generic advice.

Also, are you moored up predominantly or do you cruise regularly? That'll affect the recommendations quite a bit. Looking forward to seeing what you've got! 🚢

@Midge different setup here (static caravan rather than narrowboat) but the underlying questions are the same ones I worked through methodically before upgrading.

A few things worth establishing before anyone can give solid advice:

• What's your current battery bank capacity and chemistry?
• How many panels, what wattage, and are they in series or parallel?
• Which MPPT controller are you running?

The reason I ask is that "showing its age" could mean anything from degraded panels to an undersized controller that's throttling your harvest. Victron's MPPT calculators are worth running through even before you commit to anything.

Also worth noting — if you're on the cut regularly, shading from trees and bridges will absolutely murder a series string. That's where topology decisions get genuinely important for boats specifically.

What does your current daily consumption actually look like?

@Midge three years liveaboard means you know your consumption patterns better than most — that's actually your biggest advantage when redesigning a system.

The one thing I'd add to what's been said: narrowboats are notoriously awkward for solar real estate, and shading from locks, trees, and mooring neighbours kills more wattage than people expect. Before sizing your battery bank, I'd seriously consider a Victron SmartSolar MPPT with proper logging — run it for a few weeks and let the data tell you what you're actually harvesting, not what the panel specs claim.

On batteries, Fogstar Drift LiFePO4 cells have become genuinely popular in the liveaboard community for good reason — competitive pricing and solid BMS protection.

Also worth checking: does the existing wiring meet BSS standards? Old cobbled systems on boats can be a fire risk hiding in plain sight.

Nothing says "character building" like discovering your inherited battery bank is three separate chemistries held together by optimism and corroded terminals — been there on my own boat, @Midge.

If you're going full rebuild, Victron MPPT controllers paired with Fogstar Drift LiFePO4 cells is the combo most of us end up at after one expensive lesson in buying cheap twice. The narrowboat constraint nobody mentions: roof space calculates differently once you factor in cratch covers, vents, and that one mushroom vent that's been there since 1987 and cannot be moved under any circumstances.