Use this solar panel calculator to estimate a rough system size and panel count from annual electricity use, peak sun hours, system losses, and panel wattage. A mode estimates annual generation from a known DC system size.
Reading your solar sizing result
Annual electricity use sets the energy target. Local peak sun hours and a loss percentage estimate how much energy each of panels can produce, and panel wattage converts the system target into a whole-panel count.
A yearly utility total captures seasonal heating, cooling, and occupancy changes.
Peak sun hours are an energy-equivalent measure, not the number of daylight hours.
Run the address, roof orientation, and shade through a location-aware model before relying on the estimate.
Example: 10,500 kWh per year with 400 W panels
- For 10,500 /, 4.5 peak sun , 14% losses, and 400 panels, the engine estimates a 7.43 DC theoretical minimum.
- Rounding up gives 19 panels and a 7.60 purchased array, whose estimated annual generation is 10,735 .
- No roof-area or financial result is assumed because those optional fields are blank.
Annual kWh is the foundation
Annual is the energy target that anchors the result. Use a full 12-month utility total when possible. System size is DC capacity in ; panel count then depends on the wattage of the specific module.
Peak sun hours are not daylight hours
Peak sun hours express daily solar energy as equivalent full-power hours; they are not the total time between sunrise and sunset. The loss percentage then reduces that resource for soiling, shade, wiring, mismatch, conversion, temperature, and similar effects.
Optional roof and financial details
Panel footprint, electricity rate, and installed cost are blank by default. Enter a module area to screen panel-only roof footprint, or add your own rate and quote to see a simple first- value and payback calculation.
Frequently asked questions
What size solar panel system do I need for my home?
A first-pass size comes from annual , peak sun hours, and loss-adjusted output. Divide yearly by peak sun hours per times 365 times (1 - loss factor), then divide the resulting by panel wattage for a panel count. This calculator runs those steps and rounds up to whole panels.
How do I use a solar panel calculator for my home?
Start with your electricity use, choose the right usage period, enter local peak sun hours, and use the wattage of the panels you are considering. The calculator returns system size, panel count, roof footprint, and optional savings and cost details.
What does a solar size calculator estimate?
It estimates system size in and the number of panels needed for a target energy offset. It can also estimate annual generation from a known system size. The result is a planning estimate, not a permit layout or a guarantee of your utility bill outcome.
How do I estimate my solar system size from my electricity use?
Use a full of when possible. Divide annual use by loss-adjusted yearly peak sun hours to get required system , then divide by panel wattage and round up for whole panels. If you only know monthly use, select monthly or multiply by 12 first.
What panel wattage should I use in a solar panel calculator?
Use the rated wattage from the panel spec sheet, such as 400 . Higher-watt panels reduce the number of modules needed for the same system size, but they do not change the target set by your energy use and sun hours.