YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Inventory:
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
Solar
Minimum power required to recharge your consumption:
220V AC
Maximum power (with 25% safety margin).
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| Current (A) | Round trip < 2m | Round trip 4m | Round trip 6m |
|---|---|---|---|
| 5A (LEDs, USB) | 1.5 mm² | 2.5 mm² | 4 mm² |
| 10A (Fridge, Pump) | 2.5 mm² | 4 mm² | 6 mm² |
| 20A (Heater) | 4 mm² | 10 mm² | 10 mm² |
| 50A (DC/DC Booster) | 10 mm² | 16 mm² | 25 mm² |
| 100A (Inverter) | 25 mm² | 35 mm² | 50 mm² |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
REGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
Comparison table
| Panel watts | Wh/day (SW USA) | Wh/day (NE USA) | Wh/day (UK) |
|---|---|---|---|
| 100W | 650-750 | 500-600 | 400-500 |
| 200W | 1,300-1,500 | 1,000-1,200 | 800-1,000 |
| 300W | 1,950-2,250 | 1,500-1,800 | 1,200-1,500 |
| 400W | 2,600-3,000 | 2,000-2,400 | 1,600-2,000 |
About this tool
Off-grid solar system calculation is straightforward when you work through it systematically. Whether you're sizing a van, cabin, tiny house, or boat solar system, the same physics applies: energy in must match energy out, with storage to bridge the gap when the sun isn't shining.
Load analysis is the foundation. Every watt consumed needs to be generated and stored. Map out every load: always-on (fridge, router, sensors), scheduled (washing machine, cooking, EV charging), and intermittent (lighting, laptop, entertainment). Multiply each load's wattage by its daily operating hours to get Wh/day. Sum all values for total daily consumption.
Autonomy requirement determines storage size. A system with 2 days of autonomy needs a battery bank capable of storing 2× daily consumption — at the battery's maximum depth of discharge. LiFePO4 at 100% DOD: Battery Ah = Daily Wh × 2 ÷ 12V. AGM at 50% DOD: Battery Ah = Daily Wh × 2 ÷ 12V ÷ 0.5 (twice the capacity for same usable energy).
Solar array sizing depends on your location's solar resource. The key metric is Peak Sun Hours (PSH) — equivalent to the number of hours per day when your location receives exactly 1000W/m² of irradiance. Madrid PSH = 5.2 average annual, London = 2.8, Stockholm = 2.4. The off-grid solar calculation: Array Watts = Daily Wh ÷ PSH × 1.25 system losses × 1.1 MPPT non-ideal tracking factor.
Charge controller sizing: MPPT controllers must handle both the panel voltage (open circuit voltage determines the overvoltage protection rating) and the charging current to the battery bank. For battery protection: selected controller amperage ≥ (Array Watts ÷ Battery Voltage) × 1.25.
Inverter selection for AC loads: size to handle your largest single AC load plus 30% surge capacity. Most resistive loads draw constant power; motors (pumps, compressors) draw 2-3× rated power on startup. A washing machine drawing 2200W running requires a 3000W+ inverter to handle the motor surge.
System losses to account for in all off-grid solar calculations: MPPT controller efficiency (3-5% loss), cable resistance losses (1-3% depending on cable length and gauge), temperature coefficient of solar panels (reduced output at high temperature: -0.3%/°C above 25°C; panel surface temperature in summer can reach 60-70°C), battery round-trip efficiency (LiFePO4 97%, AGM 80-85%), inverter efficiency (typically 92-95%)..