Anyone else running a MPPT controller in a shepherd's hut through winter? Struggling with low-light performance

Been running a 400W array (2x 200W Renogy mono panels) on my hut since spring and it's been brilliant. Now we're into the darker months I'm seeing the Victron SmartSolar 100/30 barely pulling 2-3A on overcast days. Battery (a 100Ah Fogstar Drift LiFePO4) is dropping lower than I'd like overnight.

Panels are south-facing at about 35° tilt — wondering if I should steepen the angle for winter. I've read 50-60° is better for low sun elevation but the bracket setup on the hut roof makes that a faff to change seasonally.

Also noticed the controller seems to float quite early in the day even when the battery isn't really full — it's showing 100% SOC but the resting voltage suggests otherwise. Not sure if it's a calibration issue or just the BMS talking to the Victron via VE.Direct doing something odd.

Anyone gone through similar with a static or hut setup? Worth adding another panel to compensate, or is it more of a settings tweak job?

Hey @Fiona1974, totally familiar with this — shepherd's huts are a tough ask in winter given the typically compact roof space limiting your array size.

A couple of things worth checking: what's your panel tilt angle currently? Getting steeper in winter (ideally 55-60° in the UK) makes a surprising difference on low-angle December sun. Even propping the panels up temporarily can help noticeably.

Also worth looking at your battery state of charge first thing in the morning — if it's already quite high from overnight carry-over, the controller will naturally throttle back absorption current on dull days. It can look like poor performance when it's actually correct behaviour.

What's your battery bank capacity and chemistry? Lithium vs AGM makes a real difference to how aggressively the Victron will push in marginal conditions.

LisaMorgan59 | 847 posts | ⭐ Trusted Member

@Fiona1974 Oh, I feel this deeply! Had exactly the same frustration with my Renogy panels last winter on my shepherd's hut setup. A few things that genuinely helped me:

First, check your panel angles - I tilted mine steeper to about 55-60° for winter and picked up a noticeable improvement. Low winter sun hits them so much better.

Also worth looking at your battery state of charge in the morning. If they're already fairly full, the controller will naturally throttle back. What battery bank are you running?

The honest truth though is 400W in December in the UK is always going to be modest. I added a small wind turbine as backup and it transformed winter reliability completely - wind's usually plentiful precisely when sun isn't!

What part of the country are you in? Makes a significant difference.

Something nobody's mentioned yet — panel angle can be a game-changer this time of year.

On my setup I tilted my array steeper for winter (around 55-60° here in the north) and genuinely recovered a meaningful chunk of output on clear low-sun days. The maths makes sense when you think about the sun barely clearing the treeline in December.

Worth checking your Victron app history too — specifically the yield vs irradiance pattern across the day. If you're spiking briefly around solar noon and flatlining either side, that's a panel orientation problem as much as a light problem.

@Fiona1974 what's the current tilt on those Renogy panels? A lot of huts have them laid fairly flat to keep the aesthetic — which is brutal come November.

BurnShaun | 312 posts | Regular Member

@Fiona1974 Worth checking your battery state of charge first thing in the morning before any generation starts. If your batteries are sitting at 80%+ overnight, the Victron will throttle back via absorption/float earlier in the day — so those 2-3A figures might actually be the controller doing its job rather than a performance issue as such.

Also, on grey days the SmartSolar's MPPT algorithm can sometimes take a while to "hunt" for the proper power point on a fluctuating input. I found enabling the "Equalization" schedule helped mine settle quicker in low irradiance conditions.

What's your battery bank capacity? With a shepherd's hut setup you might simply be well-matched for summer but slightly undersized for December daylight hours. Sometimes adding even a small 100W panel makes a surprising difference to those marginal cloudy days.