Off Grid Load Calculator
Work out the daily energy demand of an off-grid or standalone power system by combining a continuous background load with an intermittent load. It returns the daily demand in Wh and kWh plus the average continuous power draw, ready for battery, solar and inverter sizing.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the continuous load in watts and how many hours per day it runs (often 24).
- Optionally add an intermittent load in watts and its daily run hours.
- Read the daily energy demand in Wh and kWh and the average continuous power.
How it works
Daily energy in watt-hours is the continuous load multiplied by its daily hours, plus the intermittent load multiplied by its daily hours. Dividing by 1000 converts to kilowatt-hours. The average continuous power is the total daily energy spread evenly over 24 hours, which is useful for estimating a baseline generation rate.
Worked example
Worked example. A 200 W continuous load runs 24 h and a 1000 W load runs 3 h. Daily energy is 200*24 + 1000*3 = 7800 Wh, or 7.8 kWh. Averaged over 24 hours that is 325 W.
Common mistakes
- Sizing the battery from average power instead of the full daily energy and required autonomy.
- Ignoring inverter, wiring and battery round-trip losses, which can add 20-40% to the real demand.
- Entering more than 24 total hours of operation per day for a single load.
Frequently asked questions
Does this size my battery and solar array?
No. It gives the daily energy demand. You still need to apply days of autonomy, depth-of-discharge limits and system losses to size the battery, and use local sun-hours to size the solar array.
What is the average continuous power for?
It is the daily energy averaged over 24 hours, a quick reference for the steady generation rate a source would need to just keep up with demand before losses and autonomy are added.
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Tip: Enter any known values to calculate the remaining results.
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