Anyone else running a small inverter generator alongside solar for winter backup — how are you managing the two together?

After last winter's dismal sun situation in South Wales, I've been thinking seriously about adding a petrol generator as a backup to my 400W solar setup and 200Ah lithium bank. Ended up draining the batteries to about 15% over a long grey week in January, which is further than I'd like to take them. I'm looking at something like the Honda EU22i or possibly the Hyundai HY2000Si — mainly want it quiet enough not to annoy the neighbours and efficient enough that I'm not burning through fuel just to top things off slowly.

The bit I'm struggling to get my head around is integration. My MPPT controller (Victron SmartSolar 100/30) handles solar fine, but if I'm running a generator into the same battery bank, I'd presumably need a separate AC charger like the Victron Blue Smart IP22 or similar. Has anyone got a tidy setup where the generator and solar are both feeding the same lithium bank without things getting complicated or the two charge sources fighting each other?

Also curious about runtime figures in practice — I know the EU22i is rated at around 8 hours at 25% load, but what are people actually seeing in cold weather with real charging loads? Any experiences, good or bad, welcome.

Hey @RogerHobbs, I had exactly the same issue running a van setup through a Scottish winter last year — brutal! What worked brilliantly for me was using the genny only to top the lithium bank from around 20% back up to 80%, then letting solar handle the rest. Keeps fuel consumption right down and avoids running the generator longer than necessary.

Worth getting a decent battery monitor (I use a Victron BMV-712) so you know precisely when to kick the genny on rather than guessing. Also, a 2kW inverter generator like the Honda EU20i or the cheaper Hyundai equivalent runs much quieter and is easier on fuel than a basic open-frame unit — matters a lot if you're on a campsite or residential area.

What's your current charge controller? That'll affect how you wire everything together.

Hey @RogerHobbs, welcome to the club of "solar optimists who got humbled by a Welsh winter!" 😄

One thing I'd strongly recommend looking into is an automatic transfer switch or a decent inverter-charger like a Victron MultiPlus. It lets you set a battery state-of-charge threshold — say 20% — and the generator kicks in automatically to top things up without you having to babysit it constantly.

Also worth considering: don't run the genny until the batteries are completely recovering that last 20% is horribly inefficient on fuel. Run it hard to 80% then let solar handle the rest.

A small Honda EU22i or similar inverter-type generator will also play much nicer with sensitive electronics and lithium BMS than a cheap conventional unit. Slightly pricier upfront but the cleaner sine wave is worth it.

@RogerHobbs running a motorhome through multiple UK winters has taught me that generator integration is all about the charger settings, not just the hardware.

With a Victron MultiPlus, you can set a dedicated "generator" AC input current limit so it doesn't overload a small inverter-generator's output — critical with something like an EU20i or similar. The DVCC settings in VenusOS also let solar and generator charging play nicely together without fighting over charge stages.

One thing worth considering: rather than running the genny reactively when you're already flat, configure a low-SOC automation (if you've got a Cerbo or BMV-712) to alert you before you hit 20%. Proactive short generator runs are far kinder to lithium cells than deep recovery charges.

Also factor in that petrol degrades quickly in storage — Aspen alkylate fuel is worth the premium for a backup that might sit unused for weeks.

@RogerHobbs totally feel this — ran through a February in my van with barely a scrap of solar for days on end, it's grim!

One thing worth mentioning that nobody's touched on yet: generator runtime scheduling. Rather than topping up constantly, I batch-charge once a day to maybe 90-95% and let the solar handle the rest. Saves fuel massively and your generator will thank you for it long-term.

Also with a Victron setup you can set minimum SOC thresholds that auto-remind you when to fire it up — takes the guesswork out completely.

A small Honda EU22i or similar inverter-type genny is well worth the extra cost over a cheap open-frame one — much cleaner power for your lithium charger and quieter for site neighbours too 🙂

@RogerHobbs I've got a similar situation — 400W on a garden office and a narrowboat, both Victron-based systems, so winter management is a constant headache.

One thing nobody's mentioned yet: have you looked at the Victron MultiPlus integration with a generator? The "PowerAssist" feature means your inverter/charger can blend generator output with battery power rather than just passively charging. Avoids needing an oversized generator.

Also worth checking your generator's AC output stability before connecting anything — cheaper inverter gennies (some of the Hyundai HY range etc.) can have wonky sine waves that upset sensitive chargers.

What charger are you currently running? If it's just a basic MPPT with no AC input capability, that changes the whole equation significantly. Knowing your actual winter consumption figures would help everyone give better advice too.

@RogerHobbs one thing worth flagging that often gets overlooked — generator AC output quality varies enormously, and cheap inverter gennies (even "pure sine" labelled ones) can cause issues with MPPT chargers or Victron Multis if the frequency wanders under load. Running a Victron MultiPlus on my Vivaro, I had to set the AC input current limit conservatively (around 8A on a 10A-rated genny) to stop it hunting. The MultiPlus's PowerAssist feature then makes up the difference from the battery — genuinely elegant once dialled in. Worth checking your charger's AC input sensitivity settings before assuming plug-and-play.

@RogerHobbs been in a very similar situation with a 300Ah lithium bank on my workshop setup. One thing worth considering is a proper battery-to-battery charger rather than just plugging the genny straight into an inverter/charger — gives you much cleaner charging and protects the lithium cells better.

Also, and I can't stress this enough, get a decent hour meter on the generator from day one. Helps enormously with maintenance scheduling and you'll quickly learn your actual consumption patterns across the seasons.

@GrumpyWarden mentions Victron — if you're going that route, the Cerbo GX makes managing both sources much easier, you can set proper charge thresholds so the generator only cuts in when the bank drops to say 30%.

South Wales winters are brutal for solar, two or three consecutive grey weeks is absolutely normal so plan accordingly.