Has anyone actually managed to run a 2kW inverter off a 100Ah lithium on a cloudy UK winter day?

I've been running a 200W panel setup on my Transit conversion for about eight months now and it's mostly been brilliant through spring and summer. But now we're heading into November I'm genuinely worried about keeping up with demand. I've got a Victron SmartShunt, a single 100Ah lithium (Fogstar Drift), and a Renogy 40A MPPT. Two 100W panels on the roof, wired in series.

The issue is I want to run a 2kW inverter (Giandel pure sine) occasionally for a small coffee machine and a travel hair dryer — not simultaneously, just one at a time. On a decent summer day I had no trouble, panels were pulling 18-20A through the MPPT by mid-morning. But last week in Yorkshire we had three grey days on the trot and I barely saw 5A at peak. By 6pm I was down to 40% SoC and getting nervous.

Has anyone actually stress-tested a similar setup through a proper dull UK winter? I'm wondering whether adding a second 100Ah battery is the smarter move before splashing out on more panels, or whether I should be looking at both. Also curious whether anyone's had thermal issues with the Giandel at higher loads in cold weather — mine gets pretty warm even pulling 800W.

@ShortCircuit56 brutal lesson I learned last winter on the narrowboat — a 100Ah lithium sounds generous until a grey November day in the Midlands gives you maybe 15-20% of your panel's rated output. That 200W array becomes roughly 30-40W in practice.

Running a 2kW inverter continuously off that? The maths just don't work. You'd drain a 100Ah Fogstar battery in under an hour under heavy load.

What saved me was shifting high-draw appliances — kettle, toaster, anything with an element — to shore power stops or investing in a small Honda genny for the hungry days. The inverter's fine for short bursts, laptops, phone charging. Just don't expect sustained heavy loads without either a second battery or a charging backup.

Honestly, winter UK solar is humbling. Size your storage around the worst days, not the best ones.

@ShortCircuit56 short answer — not reliably, no.

Did exactly this on my static last November with a Fogstar 100Ah and a cheap 2kW inverter. Managed maybe 20-30 mins of actual load before the battery was crying. Problem isn't just the capacity, it's that your 200W panels are probably pushing 15-25W max on a proper grey UK day. You're basically running on stored power only.

If you're serious about winter use, I'd look at:

• Doubling battery capacity minimum
• Adding even a small second panel to help offset the drain
• Being brutal about what you're actually running through that inverter

Victron's battery monitor was an eye-opener for me — seeing real numbers in real time changes how you manage everything.

What are you actually trying to run off it? That changes the advice completely.

@ShortCircuit56 the maths are pretty unforgiving here. A 2kW inverter at full load will flatten a 100Ah lithium in roughly 90 minutes if you're lucky. On a typical November day in the UK you might scrape 200-400Wh from those 200W panels — that's if the sun bothers showing up at all between the murk.

What I'd suggest is running your inverter loads through a proper watt-meter for a week so you know your actual consumption rather than worst-case figures. Most people find their "2kW inverter" is only pulling 400-600W in practice. That changes things considerably.

Also worth looking at your usage patterns — are you genuinely needing those loads simultaneously or could you stagger them? That flexibility makes a bigger difference than adding panels in my experience.

Yeah @ShortCircuit56 I hate to pile on but I'd echo what @IslandCruiser is getting at. The maths just doesn't work in your favour once you're past mid-October up here.

On a proper overcast November day in the UK you're realistically looking at maybe 1-2 hours of usable generation at best, often less. Your 100Ah lithium at a sensible 80% usable depth gives you 80Ah — that's not enormous when a 2kW inverter is pulling serious current.

What's actually helped me is being brutal about what you're running through the inverter. I shifted most of my heavy loads to direct 12V where possible and only fire up the inverter when genuinely necessary. Makes a massive difference to how long the bank lasts through a grim grey week.

What are you actually trying to power through it?

@ShortCircuit56 Worth doing the maths quickly — a 100Ah lithium at 12V gives you roughly 1.2kWh usable (assuming you're not hammering it below 20%). A 2kW inverter at full load will drain that in under 40 minutes. Obviously you won't always be running at full tilt, but on a proper overcast November day in the UK you might scrape 20-30W from those 200W panels — that's essentially nothing against a 2kW draw.

What are you actually trying to run through the inverter? If it's something like a laptop and a few USB devices, you'd be absolutely fine. If you're thinking induction hob or a fan heater, you'll want either a significantly bigger battery bank or a decent shore/generator backup sorted before the clocks go back properly. What's the use case?

Hey @ShortCircuit56, the others have covered the maths well so I won't rehash it. What I'd add from experience is that November in the UK is brutal not just because of cloud cover, but the sun angle drops so low that even a "bright" day might only give you 2-3 usable hours at maybe 40-50% panel efficiency. Your 200W array realistically becomes more like 80-100W average across the day.

Practically speaking, have you looked at what's actually pulling that 2kW? In my Transit I found shifting things like a kettle to a gas solution immediately changed the whole equation. The inverter capacity matters far less than what you're actually running through it. What appliances are you planning to power over winter?