Solar & Off-Grid Load Estimator
Select the appliances you actually plan to run, and get a real daily Watt-hour total, plus a starting-point battery and solar panel size using genuine Australian peak sun hour data.
Off-grid sizing goes wrong in one of two places almost every time: guessing appliance draw instead of using real figures, or using total daylight hours instead of genuine peak sun hours. This tool uses real appliance load ranges and real Australian regional peak sun hour data to avoid both.
Load & System Size Calculator
Appliance figures are realistic running-load ranges from real-world off-grid builds, not your specific unit's exact draw — check your own appliance's label or manual where possible. This is general information, not a substitute for a licensed solar installer's assessment for a full off-grid system.
Total daily energy use: —
Starting-point battery bank size: —
Starting-point solar array size: —
Running Watts vs Starting Watts
Every appliance with a motor or compressor (fridges, pumps, some power tools) briefly draws far more power to start than it does to run — often 2-3 times the running wattage for a second or two. This calculator uses running watts for the daily energy total, which is correct for battery and panel sizing, but your inverter itself needs to be rated for the highest single starting surge in your system, not just the running total. If you're sizing an actual inverter, check its surge rating against your single largest appliance's starting watts, not its running watts.
Why Peak Sun Hours Aren't the Same as Daylight Hours
A peak sun hour is a specific measure: the equivalent of one hour of sunlight at an intensity of 1,000 Watts per square metre — not just "an hour when the sun is up." Morning and evening sun is real daylight but weak intensity, and doesn't count the same way. Most of Australia sits between roughly 4 and 6 peak sun hours per day on average, which is genuinely generous by world standards, but winter can cut that generation by 40-60% compared to summer. Size your system around your region's lower-end or winter figure if you need reliable year-round power, not the sunny-day average.
Frequently Asked Questions
What's the difference between running watts and starting watts?
Running watts is what an appliance draws continuously once operating. Starting watts is a brief surge, often 2-3 times higher, needed to start a motor or compressor. Your inverter needs to handle the starting surge, even though daily energy totals use running watts.
Why does a peak sun hour matter more than total daylight?
A peak sun hour specifically means sunlight strong enough to deliver 1,000W/m2 - weaker morning and evening light doesn't count the same way, so total daylight hours overstate what your panels will actually generate.
Should I size my system for summer or winter sun hours?
Winter, if you need reliable power year-round - winter generation can be 40-60% lower than summer in many parts of Australia, and a system sized only for summer will fall short for months at a time.
Is this calculator a substitute for a proper solar installer assessment?
No - this gives you a genuine starting point for planning and budgeting, but a full off-grid system, particularly anything beyond a small setup, is worth having assessed by a licensed installer.
For the rest of your off-grid infrastructure planning, see our Off-Grid Energy how-to guides.