Campervan Electrical System Calculator & Off-Grid Power Builder
Add your 12V / 24V DC and 230V AC appliances to estimate daily energy usage, practical battery bank size and recommended solar array size for campervan, van conversion, motorhome and small off-grid electrical systems. This builder is designed as a practical planning tool before selecting cables, fuses, chargers and inverter equipment.
Add your electrical loads
System overview
Recommended next step
Calculate your system to see the most relevant MKGT cable route and technical next step.
How to use the campervan electrical system calculator
Add the devices you want to run in your campervan or off-grid setup, including their power in watts and average usage hours per day. Mark whether each device is a direct DC load or an AC appliance powered through an inverter. The builder then estimates total daily energy usage, practical battery size and solar panel requirements.
- Add each appliance with power (W) and hours per day.
- Choose DC load for 12V / 24V devices and AC load via inverter for 230V appliances.
- Select your system voltage, usually 12V or 24V.
- Choose battery type to reflect realistic usable depth of discharge.
- Set autonomy days to estimate how long the system should last without useful charging.
- Adjust sun hours and losses for a more realistic UK planning estimate.
What this builder estimates
This planner provides a practical estimate for:
- Daily energy use in watt-hours
- Battery bank size in amp-hours
- Practical real-world battery size recommendation
- Solar array size in watts peak
- Practical solar array recommendation
- Estimated peak system demand
What this builder does not include
- Exact inverter surge sizing for every appliance type
- Final fuse selection
- Final cable size or cable routing design
- Alternator charging limits
- Charger compatibility and charging profiles
- Battery heating or cold-weather charging limits
Typical battery assumptions
- AGM / Lead Acid: often planned around 50% usable depth of discharge
- LiFePO4: often planned around 80% usable depth of discharge
Why this matters
Campervan and off-grid systems work best when battery size, solar charging, cable size, fuse protection and inverter capacity are planned together. Undersized batteries reduce runtime, while undersized solar arrays may leave the system permanently undercharged during normal use. A larger build may also benefit from moving from 12V to 24V to reduce current and cable size.
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FAQ
Start by adding up the daily energy use of all your devices in watt-hours. Then allow for battery type, usable depth of discharge and the number of autonomy days you want. This builder estimates the battery capacity needed in amp-hours and also suggests a more practical real-world battery size.
The required solar panel size depends on your daily energy use, local weather, time of year and how much margin you want. This calculator estimates solar array size in watts peak using your daily energy demand, effective sun hours and system losses, then rounds that to a more practical solar size recommendation.
For many campervans, 12V is the most common and practical choice. Larger systems with higher inverter loads, longer cable runs or more demanding appliances may benefit from 24V because current is lower for the same power, which can help reduce cable size and voltage drop.
No. Inverter losses only apply to AC appliances powered through the inverter. Direct DC appliances such as 12V fridges, LED lights and water pumps should not be penalised by inverter efficiency.
LiFePO4 batteries are often preferred because they allow deeper usable discharge, lower weight and longer cycle life. AGM and lead-acid batteries can still work well in some setups, but they usually need more total capacity for the same practical usable energy.
Yes. Although it is designed around campervan electrics, the same planning logic can also be useful for boats, off-grid cabins and other small standalone battery and solar systems.
No. This is a practical planning tool only. Final system design should still be checked against real appliance loads, charging sources, battery specifications, inverter surge requirements, cable sizing, fuse protection and safe installation practice.
These calculator results are provided as a practical technical guide only. Final battery sizing, solar array size, cable size, fuse protection, charging setup, inverter selection and installation method should always be verified against the real application, equipment specifications, operating temperature, charging profile and installation environment.