Anyone else finding 400W panels overkill for a small shepherd's hut setup?

Finally got the solar sorted on my hut after months of faffing. Went with two 200W Renogy panels wired in series feeding into a Victron SmartSolar 100/30 MPPT, with a pair of Fogstar 100Ah lithium batteries in parallel. On a decent day in July I was hitting 380W peak — genuinely more than I expected for South Yorkshire.

The thing is, for what I actually use in the hut — a few LED lights, phone charging, a 12V fan, and occasionally a small 12V compressor fridge — I'm barely scratching the surface of that capacity. Batteries are at 100% by 10am most summer mornings and the MPPT is throttling back before lunch. Wondering if I over-specced it slightly.

Anyone else in a similar boat with a small structure? Curious whether people bother right-sizing their systems or just go bigger "for future expansion" and accept the inefficiency. Also wondering if there's any point adding a small inverter for 240V stuff or whether that's just opening a can of worms for a weekend retreat.

@WattCharlie series wiring on those panels is the right call — you'll see noticeably better MPPT performance, especially on overcast days when voltage holds up better than current.

400W does sound generous for a shepherd's hut, but honestly you'll thank yourself in October-February when the UK sun essentially retires. I run a similar setup on my static caravan and even with "overkill" panel wattage, winter generation can be surprisingly grim.

One thing worth checking in the Victron app — are you seeing your absorption and float stages completing cleanly? With Fogstar lithiums you want to nail the charge profile settings, as the default Victron LiFePO4 preset is occasionally a bit conservative on the absorption voltage.

What's your actual daily consumption looking like? That'll determine whether 400W genuinely is overkill or just feels like it right now during summer months.

Just wanted to add — don't overlook the seasonal drop-off with that setup. Even with 400W nominal, you're realistically pulling maybe 150-180W on a grey December day in the UK, which is worth factoring into your winter usage plans. I've got a similar arrangement on my hut in Wales and found having a small backup like a 100W folding panel for top-ups during gloomy stretches was a lifesaver. Also worth checking your Victron app regularly through autumn — the MPPT history graphs are brilliant for spotting patterns before they become problems. Overall though, sounds like a cracking setup! 🙂

@LisaMorgan59 makes a really good point about seasonal drop-off — worth adding that if you're using the hut through winter, you'll also want to think about panel angle. Most fixed installations are set for a compromise angle around 35-40 degrees, but tilting steeper (closer to 55-60 degrees) through the darker months can claw back a fair bit of generation when the sun sits low.

@WattCharlie that Victron/Fogstar combination is solid by the way — the SmartSolar integrates beautifully with the Victron app so you can actually see exactly what you're pulling and generating in real time, which takes a lot of the guesswork out. Have you set up VictronConnect yet? Makes tweaking the charge profile for those lithiums much easier than fiddling with DIP switches.

Curious about this from a boat perspective — does anyone know how much the efficiency drops when those Renogy panels get even partial shading? On water I'm constantly dealing with shadows from the mast and rigging, which is why I ended up wiring mine in parallel rather than series. Wondering if that trade-off would apply to a shepherd's hut too, or if shading is less of a concern there?

Also, what's @WattCharlie's battery capacity? 400W of panels into 200Ah of Fogstar lithium seems like it could be well-matched, but I'd imagine going much smaller on the battery side might cause issues with the Victron not having anywhere to dump charge on a clear day?

@WelshVanLifer panel temp makes a bigger difference than most people realise — they're actually more efficient in cold, crisp winter air than on a scorching August afternoon. The efficiency loss from heat is why I angle mine more steeply in summer despite the higher sun, helps the breeze get underneath and cool them off a bit.

On the original question — I ran a similar 400W setup on my motorhome for two years before moving to a shepherd's hut conversion. Honestly for a modest hut with LED lighting, a 12V fridge and phone charging, 400W feels about right rather than overkill. You'll thank yourself come November when you're limping along on three hours of usable light and still keeping the Fogstats reasonably topped up.

@BayPete is absolutely right on the temperature coefficient point — worth knowing that most standard poly/mono panels lose roughly 0.3–0.5% per degree Celsius above 25°C STC rating, so a hot summer roof can cost you meaningful output.

To directly answer @WattCharlie's original question though — 400W into a 100/30 MPPT on a modest shepherd's hut is genuinely sensible rather than overkill. The 30A controller limits your charge current anyway, so you've got headroom for poor winter angles and shading without undersizing. Running my static caravan setup I deliberately oversized panels relative to controller capacity for exactly this reason — December and January you'll thank yourself.

The Fogstar 100Ah pair is the real limiting factor here. Two 100Ah in parallel gives you roughly 200Ah usable, which with 400W input should recover comfortably overnight between morning and afternoon on most spring/autumn days.

Something I noticed with my static caravan setup — panel sizing looks "overkill" until you hit a grim November fortnight where you're pulling everything back through compromised irradiance and high internal resistance from the cold. Those 400W nominally become closer to 180-200W usable on a proper grey day.

@WattCharlie your 100/30 is actually the bottleneck there before the panels are — that controller tops out around 390W input at 12V anyway, so you've landed in a sensible spot without really overspeccing anything. I'd call it well-matched rather than overkill personally.

@HiluxConvert hit on something I learned the hard way with my garden office build. I'd convinced myself 400W was generous for summer — then October arrived and I was watching my Victron app like a anxious parent. Those short grey days expose every watt of under-sizing ruthlessly.

The way I look at it now: panels are cheap real estate. Battery capacity is where the real money goes. If you've got roof space on that hut, the marginal cost of an extra panel is nothing compared to a winter spent nursing a depleted bank.

400W isn't overkill. It's approximately right.