Before you start chasing, get clear on what's actually happening. Which of these is closest to your situation?
The cause and the fix are different for each. Let's go through them.
Most common causes, in likelihood order:
The most underestimated cause. A small branch shadow across any part of any panel can collapse output to near-zero. Walk around the van and look up. If anything is over the roof, move the van or trim the obstruction.
If the battery is at 100% (or very close), the regulator stops pulling from the panels — there's nowhere for the energy to go. Check SOC on your monitor. Solar will resume when you start drawing again.
Less common but possible — a roof junction or connection has come loose. If everything else looks fine and you're still at 0A, contact your nearest Mars branch.
The MPPT/PWM controller may have an error state, blown fuse, or wiring issue. Check the regulator display (if accessible) for fault codes. Don't try to fix the wiring yourself — log a ticket.
If you're seeing some current but not what you expected:
Dust, sap, bird droppings, pollen, salt — all reduce output significantly. A quick wipe-down with water and a soft cloth often restores 20–40% of "lost" output. Do this whenever the panels look anything less than clean.
Even partial shading — a TV antenna, satellite dish, awning support, rooftop vent — across one cell drops output across the whole panel disproportionately. Walk around the van mid-morning and check for shadows hitting any part of the roof array.
Peak production is roughly 10am to 3pm. Early morning and late afternoon, even in full sun, produces a fraction of midday output. If you're checking output at 8am or 5pm, low numbers are normal.
Fixed roof panels are designed for the sun being overhead. In winter (especially southern states), the sun sits lower and the geometry is less favourable — expect 40–60% of summer output.
Counter-intuitive but real — panels lose efficiency as they get hot. A panel at 60°C produces 10–15% less than the same panel at 25°C. Hot day, full sun, exposed roof = somewhat less output than you'd expect from the sunshine alone.
Heavy cloud knocks output down to 15–30% of rated. Thin overcast is less brutal — 50–70%.
Solar looks normal during the day, but you're not getting to 100% by sunset.
The most common cause. Run the maths:
If consumption ≥ production, the battery never catches up. Reduce consumption (turn the inverter off when not used, run the fridge cooler, etc.) or increase production (portable panel, move out of shade).
One cloudy day means a partial top-up. Three cloudy days in a row and you've fallen well behind. Once consumption normalises with sunny days, the battery recovers — but it takes time.
Fridges work much harder in 35°C ambient than in 20°C ambient. The same fridge can double its daily energy use in hot weather. If your battery is keeping up in spring but struggling in summer, this is often why.
LiFePO4 batteries don't sit at exactly 100% the way an AGM might. The regulator may show SOC at 99% or 98% and stop charging — that's normal, not a fault. The battery is effectively full.
The most common reason. An inverter switched on but with no load still draws 1–2A continuously — over 8 hours overnight that's 8–16Ah lost. Always switch the inverter off at night unless you're running something through it.
The fridge cycles regardless of day or night. In hot weather it's the dominant overnight load. If you've turned the fridge temperature down (colder), it'll run more.
Diesel heaters use very little 12V (just the fan), but it's continuous when running. On a cold night, the heater fan can pull 1–2A all night.
Phone chargers, satellite/4G boosters, USB ports with stuff plugged in, BMS standby — small loads add up. Audit what's actually drawing current overnight by switching things off one at a time and checking the monitor.
If you're not sure where the problem is, work through in this order — quickest checks first:
Related: How Your Mars Solar System Works· Adding a Portable Panel· Battery Basics