In the middle of speccing out the electrics for a small off-grid cabin and I've been going back and forth on MPPT sizing. Currently running two 200W Renogy panels in series (24V nominal system, so ~70V Voc in cold conditions) feeding into a 200Ah Fogstar Drift LiFePO4. The 100/20 would technically handle the array but I'd be sitting right at the limit on charge current — 20A into a 24V bank is only 480W usable, which wastes maybe 15-20% of the array capacity on a good day.
The 100/30 is roughly £40-50 more from the usual suspects (Bimble, Amazon, etc.) and gives me 30A — so 720W capacity at 24V, which means I could bolt on a third 200W panel later without touching the controller. That future-proofing argument feels solid but I'm wondering if I'm over-engineering a cabin that mostly runs LED lighting, a 12V compressor fridge, and occasional laptop charging. Total daily load is probably 80-100Wh realistically.
Has anyone actually saturated a 100/20 in real-world UK conditions with a similar array? I suspect cloud cover and our general lack of sun hours means I'd rarely hit true 20A anyway, which makes the upgrade feel less justified. But then again the Victron app integration and load terminals are identical between the two so it's not like the 100/30 adds complexity.
Genuinely torn — is the £45 delta worth it for headroom you'll likely never use in a cloudy climate, or is that money better spent elsewhere in the build?