Off-Grid Van Electrical Calculator
Work out exactly what battery, solar and inverter size your campervan build needs — based on the appliances you actually run, not a generic template.
Open the Calculator ↓Size Your System in 60 Seconds
Add your appliances below, set your build preferences, and get a personalised sizing blueprint.
1. Your Build Setup
2. Your Appliances
Tick AC only for appliances that run through the inverter (kettle, microwave, laptop mains charger). 12V items like fridges, LED lights, and USB charging draw straight from the battery.
| Appliance | Watts | Hrs/day | AC? |
|---|
Your Sizing Blueprint
Estimates only, based on typical UK component pricing and a 20% real-world efficiency buffer. Always size with a 20–25% safety margin above minimums, and consult an installer for gas/electrical safety compliance.
How This Calculator Works
Sizing an off-grid electrical system comes down to four numbers: how much energy you use per day, how much battery capacity stores it, how much solar replaces it, and how big an inverter runs your AC appliances. Here’s exactly what’s happening behind the scenes.
1. Daily Energy Consumption (Wh)
Every appliance you add is multiplied by its daily runtime and summed together.
2. Battery Capacity (Ah)
Lithium (LiFePO4) batteries can safely use around 85% of their rated capacity without damage, while AGM/lead-acid batteries should only be discharged to about 50% to protect their lifespan — that’s why lithium setups need a smaller Ah bank for the same usage.
3. Solar Array Size (W)
The UK averages roughly 2.8 usable peak sun hours per day year-round, versus around 3.8 in much of the US and Canada — which is why the same appliance load needs a bigger solar array in the UK.
4. Inverter Size (W)
The inverter must cover every AC appliance you might run at the same time, not just your single largest one — the 25% margin on top covers startup surge (fridges and pumps especially) without tripping the inverter.
Frequently Asked Questions
How big a battery do I need for a campervan fridge?
A typical 12V compressor fridge draws 40–60W and runs roughly 8 hours of compressor time per day (cycling on and off), using around 350–480Wh daily. With a 2-day lithium setup at 12V, that’s roughly 70–95Ah on its own — use the calculator above with your fridge’s actual wattage for an exact figure.
How much solar do I need for a van conversion in the UK?
Most UK van builds with a fridge, lighting, and device charging need 300–450W of solar to keep up through the year, though winter months with fewer daylight hours may need a generator or shore power top-up regardless of array size.
Should I choose lithium (LiFePO4) or AGM batteries?
Lithium costs more upfront but lasts 8–10x longer, weighs less, and lets you use far more of its rated capacity — which usually makes it cheaper per usable Ah over the system’s lifetime. AGM is a lower-upfront-cost option for occasional or budget builds.
What size inverter do I need for a campervan?
Size your inverter to your single largest simultaneous AC load plus a safety margin for startup surge — for most builds running a laptop charger, kettle, or small appliances, 1000–2000W pure sine wave covers it. Avoid modified sine wave inverters for sensitive electronics.
Van Electrical Guides
Lithium vs AGM: Full Comparison
Cost, lifespan, and weight breakdown for van batteries.
Best Solar Panels for Van Conversions 2026
Flexible vs rigid panels, mounting, and wiring tips.
Pure Sine vs Modified Sine Inverters
Which appliances actually need pure sine wave power.