Home & off-grid load planning
Off-Grid Solar Load Calculator
Build the appliance list behind your solar system. Add watts, quantity, hours per day, and optional surge for each load. The result separates daily Wh for energy sizing from running and startup watts for inverter checks.
Build your daily solar load list
Your planning estimate
Local calculationEnter your values, then calculate. Results will show the formula inputs and rounding used.
Formula used
daily load energy = Σ(appliance watts × quantity × hours per day) + standby watts × 24Watt-hours measure daily energy; watts measure power at a moment. The optional standby field makes always-on or ghost loads explicit, while the shared load aggregation module keeps running power and listed startup power separate.
See the full assumptions and rounding policy.
Maintenance and verification
The calculator calls the shared, tested TypeScript calculation modules documented in the methodology. Automated tests cover published examples, invalid inputs, rounding, and result invariants.
SolarMathKit maintains this implementation. The review is an internal technical check, not an independent engineering certification.
Worked example: a small daily load list
A 100W appliance runs 8 hours, two 15W devices run 2 hours, and a 40W device runs 6 hours.
- 100W × 1 × 8h = 800Wh.
- 15W × 2 × 2h = 60Wh.
- 40W × 1 × 6h = 240Wh.
- Daily total: 800 + 60 + 240 = 1,100Wh.
Common mistakes to avoid
- Using watts as though they were watt-hours.
- Adding a compressor's surge watts to every hour of energy use.
- Forgetting routers, controls, and other always-on or ghost loads.
- Leaving duty-cycled equipment at nameplate watts for 24 hours without measurement.
- Sizing panels before checking a representative 24-hour load.
Questions people ask
How do I calculate my home load for solar?
List each appliance, multiply its watts by quantity and hours per day, then add the rows. Use the optional standby field for loads that stay on close to 24 hours. The daily watt-hour total is the number to carry into panel and battery sizing.
What is the difference between watts and watt-hours?
Watts describe power at a moment; watt-hours describe energy used over time. Running and startup watts help with equipment checks, while daily watt-hours drive battery and panel sizing.
Is this a solar panel sizing calculator?
No. This tool establishes the load side only. Send the daily watt-hours to the solar panel calculator when you are ready to add sun hours and system losses.
What should I enter for a refrigerator?
A plug-in energy meter or a documented 24-hour energy figure is better than multiplying compressor nameplate watts by 24. If you only have watts, estimate the hours the compressor actually runs.
What is an always-on or ghost load?
It is the power used by equipment that remains energized even when its main job is idle, such as a router, controller, monitoring device, or standby electronics. Enter that power separately when it is not already represented by an appliance row.
Why is surge shown separately?
Startup power helps with inverter and equipment-limit checks, while daily watt-hours drive energy storage and production sizing.
Can I use the quick-add examples?
Yes, as editable starting points only. Replace their values with measurements or current nameplate data.