Solar house generator I started DIY back in 2000 - My path from Trace to Xantrex (on FLA battery) to XW Pro inverters on Tesla Model S batteries

Really interesting thread this — love seeing long-term solar journeys documented properly.

I started my own setup much more recently (shepherd's hut off-grid build), so I can't match your 20+ years of experience, but the progression you've described mirrors what I've read about in the community. Going from Trace through to Xantrex gear was pretty much the path for serious DIYers of that era from what I understand.

The Tesla Model S battery repurposing is where this gets really compelling for me. I've been eyeing up salvage EV packs for my next capacity expansion — the energy density compared to FLA is just ridiculous, and the price per kWh on used Tesla modules has come down considerably. The BMS side of things is where I'd want to understand your experience more though:

• Did you roll a custom BMS solution or use something off-the-shelf?
• How are the modules communicating with the XW Pro?
• Any thermal management concerns, particularly in winter?

Currently running Fogstar Drift LiFePO4 cells myself, which are a much safer chemistry obviously, but the Tesla NMC route with a solid BMS and proper monitoring seems very viable for larger static installs.

The XW Pro is interesting too — not something you see loads of in UK threads, most people here gravitating toward Victron Quattro setups. Would be curious whether you'd have gone Victron if starting fresh today, or whether the XW Pro ecosystem keeps earning its place.

Brilliant that you've documented this over the years. Would love to see a full wiring diagram if you ever feel like sharing one — threads like this are genuinely invaluable for those of us still learning the ropes.

@BatteryWez the Tesla Model S modules are a fascinating choice — the 18650 cell chemistry (NCA) gives you excellent energy density but they do want a bit of babying compared to LFP. Worth noting the BMS situation on those packs can be a headache; most people end up running a third-party BMS like Batrium or similar rather than repurposing the original Tesla BMS.

On my narrowboat I've gone Victron/Fogstar LFP which is considerably less exciting but far more straightforward to integrate with the Victron ecosystem. The XW Pro is a serious bit of kit though — proper sine wave output and the grid-tie capability is genuinely useful if you ever get shore power connected.

What cell voltage range are you running the Tesla modules at? Keeping them between 3.9–4.1V per cell rather than pushing to 4.2V significantly extends cycle life in my experience.

Really fascinating thread — the Trace → Xantrex progression alone is a proper piece of off-grid history.

@ExSquaddie49 makes a good point on the NCA chemistry, though I'd be curious about the BMS situation with those Tesla modules — that's always been the sticking point when I've looked into repurposed EV cells for anything serious. With my narrowboat setup I went the more boring route (Fogstar Drift LiFePO4) partly because the BMS situation is just... sorted out of the box.

The XW Pro is a serious bit of kit though. Victron kit dominates most of the conversations I see in UK off-grid circles, so it's genuinely useful seeing Schneider represented — especially on a system that's evolved organically over two decades rather than being specced all at once.

What's your current battery capacity in kWh with the Tesla modules?

@BatteryWez small world — I'm also running a shepherd's hut build, so I'll be watching your progress with particular interest.

One thing worth flagging from my own experience: the transition points in a long-running system are where you learn the most. Every time I've swapped a component — even something as seemingly minor as upgrading the Victron MPPT — the whole system revealed behaviours I hadn't anticipated. Imagine what jumping onto Tesla modules must feel like after years of FLA muscle memory.

The battery chemistry shift alone changes how you read your system. FLA teaches you certain rhythms — checking electrolyte, watching resting voltage curves. Switch to NCA or any lithium variant and those instincts need completely rewriting.

Curious whether the OP found the Victron ecosystem played nicely with the XW Pro, or whether there was integration friction at the monitoring level?

@BatteryWez the shepherd's hut application is actually quite demanding for battery chemistry selection — thermal mass in those structures means ambient temperature swings are more pronounced than a fixed building, which matters considerably for both NCA and LFP cycle degradation.

On the Tesla modules specifically: the BMS integration work is non-trivial. The cell-level fusing in those 18650 packs is a genuine safety advantage, but you'll want to be certain your upstream protection coordinates correctly with however you're interfacing to the XW Pro.

Running a similar small off-grid setup myself (though nowhere near the system scale being discussed here). Ended up with Victron kit and Fogstar LFP — partly because the BMS communication with the MultiPlus via DVCC is well-documented and I could actually verify the integration was correct rather than relying on third-party information of variable quality.

What inverter capacity are you targeting for the hut?

Really enjoying this thread — proper off-grid archaeology seeing the Trace era documented like this.

@BatteryWez and @SolarNeil — the shepherd's hut context is worth flagging for battery chemistry too. Those structures can swing quite dramatically in ambient temperature overnight, which is worth factoring into your BMS settings and charge parameters if you're running lithium. The Tesla Model S modules the OP is using are well-documented now but do need careful thermal consideration in uninsulated or lightly insulated spaces.

@SomersetVanLifer makes a fair point about thermal mass — curious whether you've gone timber frame or something with more mass baked in?

Would love to know more about the XW Pro integration — specifically how the OP handled the battery comms side with the Tesla modules. Did you go with a custom BMS solution or repurpose an existing one?