A badly sized solar system means a fridge that dies after 3 days, an underused MPPT, and €600 wasted. This guide gives you the exact formulas, field-tested product comparisons, and the 7 mistakes 80% of van lifers make.
400 Wc
standard full-time van setup
0,78
residential Performance Ratio (IEC 61724)
€1 580
complete full-time config budget
+29%
measured MPPT vs PWM gain
The first sizing mistake always starts here: people eyeball it and undersize by 40%. List every device with its power draw (W) and daily use (h/day).
| Equipment | Power | Use/day | Wh/day | Type |
|---|---|---|---|---|
| 40 L compressor fridge | 45 W avg. | 24h | 480–880 Wh | Critical |
| Laptop 15" | 45–65 W | 5h | 225–325 Wh | Variable |
| External monitor 24" | 22 W | 4h | 88 Wh | Variable |
| LED lighting (4 strips) | 20 W total | 4h | 80 Wh | Low |
| Smartphone + tablet | 15 W | 2h | 30 Wh | Low |
| Drone charging | 60 W | 1h | 60 Wh | Occasional |
| 12V water pump | 6 W | 0.3h | 2 Wh | Negligible |
| TYPICAL TOTAL (full-time van) | 965–1 465 Wh/day | |||
Wc sizing formula
Wc = (Wh/day × 1,25) ÷ PSH
PSH = Peak Sun Hours (source: PVGIS). 1.25 = safety coefficient (wiring + MPPT + temperature losses).
Example: full-time van, 1 200 Wh/day, central France (PSH = 4.5h) → Wc = (1 200 × 1,25) ÷ 4,5 = 333 Wc → pick 400 Wc
| Criterion | Flexible | Rigid | Winner |
|---|---|---|---|
| Efficiency | 18–21% | 22–23% | Rigid |
| Warranted lifespan | 10–15 years | 25 years | Rigid |
| Weight (200 Wc) | 2,4 kg | 13–16 kg | Flexible |
| Curved-roof mounting | ✓ Glue + screws | ✗ Brackets | Flexible |
| Ventilation | Glued → +15°C → -8% | Ventilated → stable | Rigid |
| Price per Wc (2026) | €1,50–2,00/Wc | €0,90–1,40/Wc | Rigid |
| Hail/impact resistance | Moderate | High (3mm glass) | Rigid |
The glued-flexible trap: with no air gap, a flexible panel reaches 85°C → efficiency -10%, lifespan halved. Mount on spacer rails of 2–3 cm minimum.
A PWM wastes 20-30% of the energy produced. On 400 Wc, that's 400-600 Wh lost per day.
MPPT vs PWM gain — real-world example
200 Wc panel, Voc = 22V, Vbatt = 13.2V
PWM: 200/13.2 × 0.75 = 11,4A → 150W effective
MPPT: 200 × 0.97 = 194W effective — i.e. +29%
| Controller | Current | Price | Connectivity | Verdict |
|---|---|---|---|---|
| Victron SmartSolar MPPT 40A | 40A | €145 | Bluetooth + app | Market reference |
| Renogy MPPT 40A | 40A | €85 | LCD only | Good value |
| EPEver Tracer 40A | 40A | €70 | RS485 optional | Budget |
| Victron SmartSolar 100/50 | 50A | €180 | Bluetooth + VE.Direct | 400+ Wc recommended |
LiFePO4: 10× more cycles, 50% lighter, 100% usable capacity (vs 50% for AGM).
Battery capacity formula
Ah = (Wh/day × Days of autonomy) ÷ (V × DoD)
DoD = 0.8 for LiFePO4 / 0.5 for AGM. Example: 1 200 Wh/day × 2 days ÷ (12 × 0,8) = 250 Ah
Cable gauge formula
S (mm²) = (I × L × 2) ÷ (ΔV × 56)
ΔV = max voltage drop 3% of 12V = 0.36V. 56 = copper conductivity at 20°C.
| Run | Current | Min. gauge | Fuse | Note |
|---|---|---|---|---|
| Panel → MPPT | 12A/panel | 4 mm² solar | No (MPPT protects) | Double insulation |
| MPPT → Battery | 30–50A | 10 mm² | 60A fuse, battery side | As short as possible |
| Battery → Breaker | 100A max | 25 mm² | 100A fuse (ANL) | Within 30 cm |
| Distrib. → 12V fridge | 10A | 2,5 mm² | 15A fuse | Direct cable |
| Distrib. → lighting | 4A | 1,5 mm² | 5A fuse | Can be shared |
Never skip the ANL fuse on the battery side. It must be within 30 cm of the terminals. It's the only protection against fire in case of a short circuit.
| Item | Weekend (200Wc) | Full-time (400Wc) | Pro (600Wc) |
|---|---|---|---|
| Solar panels | €320 (2×100Wc flex) | €580 (2×200Wc rigid) | €820 (3×200Wc rigid) |
| LiFePO4 battery | €280 (100Ah) | €520 (200Ah) | €750 (300Ah) |
| MPPT controller | €85 (Renogy 30A) | €145 (Victron 40A) | €180 (Victron 50A) |
| 12V/230V inverter | €65 (300W) | €180 (1000W) | €320 (2000W) |
| Wiring + fuses | €60 | €95 | €140 |
| Accessories | €40 | €60 | €80 |
| TOTAL | €850 | €1 580 | €2 290 |
You "estimate" 400 Wh/day, the reality is 900 Wh. Measure with a power meter for 3 days.
✓ Fix: A meter like the Shelly 1PM on each circuit for 72h
€299 kits include a PWM. You lose 20-30% of your energy immediately.
✓ Fix: Buy each component separately — MPPT Victron or Renogy
A 2.5 mm² cable on 30A heats to 90°C+. In a van, that's a fire starting.
✓ Fix: Compute each gauge: S = (I × L × 2) ÷ (ΔV × 56)
Without an ANL fuse within 30 cm of the battery, a short circuit = your van in flames.
✓ Fix: Always an ANL 100A fuse on the main positive cable
Direct glue → 85°C → efficiency -10%, lifespan halved.
✓ Fix: Spacer rails of 20mm minimum or ventilated rigid panels
AGM profile = permanent undercharge. You only use 80% of the capacity.
✓ Fix: Li-Ion profile, absorption voltage 14.6V, float 13.6V
Without a shunt like the Victron BMV-712, the battery shuts off by surprise.
✓ Fix: Victron BMV-712 (€85) or an integrated Smart BMS shunt
For a van with a 12V fridge, LED lighting, a laptop and chargers, a 200 to 400 Wc system is standard. In France, 200 Wc generates around 800 Wh/day in summer (south) and 400 Wh/day in winter (north). Work out your real needs: total Wh/day divided by the peak sun hours of your area (3 to 5h per PVGIS).
Rigid panels (tempered glass) offer better efficiency (22-23% vs 18-21%) and a longer lifespan (25 years vs 10-15 years). Flexible ones fit curved roofs and weigh 60% less. For a full-time van, rigid panels with ventilated mounting are recommended if the roof allows it.
Always MPPT for a permanent van installation. An MPPT controller recovers 10 to 30% more energy than a PWM, especially on cloudy mornings and in winter. The extra cost (€50-100) is paid back within a few months. The Victron SmartSolar MPPT is the market reference.
Use the formula: S (mm²) = (I × L × 2) / (ΔV × 56). For 20A over 4m of cable with a max 3% voltage drop on 12V (0.36V): S = (20 × 4 × 2) / (0.36 × 56) = 7.9 mm². Pick 10 mm². Between panels and MPPT: 4mm² solar cable minimum with MC4 connectors.
Realistic budget for a 400 Wc / 200Ah LiFePO4 system: rigid 400Wc panels (€400-600), 200Ah LiFePO4 battery (€450-650), Victron 40A MPPT controller (€120-180), cables + fuses + connectors (€80-120). Total: €1 050 to €1 550.
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