Solar Load Calculator — Free Online
Start with the sample home, change the quantities to match your house, and instantly see the running load, daily units, panel count, inverter size and battery estimate.
Total running load
656 W
If everything selected runs together
Daily electricity use
5.82 units
Estimated kWh per day
Recommended solar
1.76 kW
3 × 585W panels
Inverter size
1 kW
Includes a 25% safety margin
1. Tell us what you run
Set quantity and average daily hours. Change watts if your appliance label says something different.
2. Sun, panels and backup
5–6 hours is a reasonable starting estimate for many sunny regions. Shade and panel direction matter.
Backup avoids running every heavy appliance at once. Pumps, fridges and ACs also need starting/surge capacity.
How to use the Solar Load Calculator
- 1
Enter your appliances
Set how many fans, lights, ACs and other items you have, and roughly how many hours each runs per day.
- 2
Set sun & panel size
Five to six useful sun hours is a sensible starting point in many sunny regions; adjust for shade, season and your city.
- 3
Choose backup needs
Decide whether batteries must run only fans and lights or a larger part of the home, then compare lithium and lead-acid estimates.
Why use Tools Stars for this?
- Ready watt estimates for common home appliances
- Add custom appliances using the watt label on your own device
- Panel count, inverter kW, battery kWh/Ah and roof-area estimates
- Separate running-load and daily-unit calculations — no confusing them
- 25% inverter safety margin and realistic system-loss allowance included
Frequently asked questions
What is the difference between running load and daily units?
Running load is watts being used at one moment and mainly decides inverter size. Daily units are watt-hours accumulated through the day and mainly decide how many solar panels and how much battery energy you need. A 1,000W iron used for 30 minutes uses only about 0.5 units.
Why is the fridge set to 10 hours instead of 24?
A refrigerator is plugged in all day, but its compressor cycles on and off. Ten “effective running hours” at its rated watts is a starting estimate. Older or large fridges can use more; check the energy label or use a plug-in energy meter for precision.
Can this calculator tell me the exact system to buy?
It gives a strong first estimate, not a final engineering design. Starting surge from motors, wiring length, roof shade and direction, battery brand limits, future load and local net-metering requirements should be checked by a qualified installer.
Should I size batteries for the full house?
Usually no. Batteries are expensive, so most homes back up fans, lights, TV, router and fridge while avoiding ACs, irons, heaters and pumps during load-shedding. Choosing a lower backup percentage can reduce battery cost dramatically.
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