Formula
One panel's daily output is its kilowatts, times sun hours, times what remains after losses:
panels = daily kWh / (panel kW × sun hours × (1 − loss))
The count is rounded up to a whole panel. Peak sun hours are yours to type. This page has no city irradiance table.
Assumptions
- Every panel is the wattage you enter.
- Peak sun hours already describe the site.
- The loss percent covers temperature, soiling, and inverter loss as one number.
Worked example
30 kWh a day from 400 watt panels, 5 peak sun hours, and 14% loss needs 18 panels.
Input definitions
- Peak sun hours
- The equivalent hours at 1,000 watts per square meter. You type the figure for the site.
- System loss
- The percent of nameplate output that does not become usable energy.
Limitations
This is a planning estimate. The rate, sun hours, and losses are numbers you type. It is not a utility bill, a solar design, or a room-by-room load calculation.
Questions
Why is the count rounded up?
A fraction of a panel is not something you buy. The array kilowatt page leaves the result as a size instead of a count.
Does this look up my city's sun?
No. Peak sun hours stay in the field so the page does not invent a climate.