A clear, no‑nonsense guide to sizing your van's electrical system for real off‑grid use. Wildbox builds expedition‑grade systems for people who actually go places.
This page helps you plan sensibly before you buy parts — and shows where DIY builds go wrong. Plan for winter/shoulder seasons even if you dream of summer Alps.
Trip length & season matter more than anything else. Solar varies massively through the year, and big AC appliances change the game.
Plan for winter/shoulder seasons even if you dream of summer Alps. You can always throttle back.
List each device, its power (W) and hours/day (or duty cycle). Wh = Watts × Hours. Sum all Wh to get your daily energy use.
A kettle, induction, or air fryer means you're sizing for a house, not a van. Either accept the bigger system (cost/weight) or cook on gas/diesel.
Usable battery (kWh) = Daily Wh × Autonomy days ÷ Depth‑of‑Discharge allowance
Plan on 80–90% usable. 100 Ah @ 12.8V ≈ 1.28 kWh.
Weight: ~11–13 kg per 100 Ah
Plan on 50% usable. Heavy and larger; only pick for budget reasons.
Weight: ~25–30 kg per 100 Ah
1.1 kWh/day × 2 days ÷ 0.85 ≈ 2.6 kWh usable
≈ 2 × 12V 100 Ah LiFePO₄ (2.56 kWh)
LiFePO₄ should not be charged below 0°C unless heated/with suitable BMS. Capacity also dips in the cold — build margin.
Daily solar harvest ≈ Panel Watts × Peak‑Sun‑Hours × 0.6–0.75
(system losses, angle, temperature)
Trees, clouds, and low sun make it worse. MPPT charge controllers beat PWM.
Treat solar as your summer top‑up and rely on alternator DC‑DC charging to guarantee winter autonomy.
Summer (good day):
600W × 4 PSH × 0.7 ≈ 1.7 kWh/day
Winter (same array):
600W × 1 PSH × 0.6 ≈ 0.4 kWh/day
The backbone of a reliable build (works with smart alternators).
30A on 12V ≈ 360 Wh per hour of driving
60A ≈ 720 Wh/h
Fit combined AC charger sized to ~10–20% of battery Ah (e.g., 30–60A for 300Ah bank).
Only if you absolutely must (noise, smell, storage). If you're at this point, re‑think loads first.
Designing around a domestic kettle/induction then balking at the cost/weight. Decide your cooking strategy early.
Assuming summer solar output will hold in November. It won't.
Oversizing the inverter and leaving it on all day (silent battery killer).
Skipping DC‑DC on smart‑alternator vehicles.
Under‑fusing or using cable that's too small for the currents.
No plan for cold‑weather charging of LiFePO₄.
Daily Wh = Watts × Hours
Usable kWh = Daily Wh × Days ÷ DoD
kWh/day ≈ Panel W × PSH × 0.6–0.75
We design, build, and test complete off‑grid systems — from tidy weekenders to expedition‑ready rigs.
We map your loads, space and budget into a full layout, weight model and power model — sized for a British winter, not a summer photo shoot.
A paid design service, starting with a free 30-minute discovery call. The fee is credited against your build.
Saves months and prevents expensive re-work — whether you build it, or we do.
30-minute power planning call — bring your load list, we'll stress‑test the plan.