Solar Panel Number Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from U.S. Department of Energy: Solar Energy Technologies. Last verified 2026-06-23.

The Solar Panel Number Calculator computes solar panel number from the relation panels = ceil( daily kWh / (sun hours x performance ratio) x 1000 / panel watts ). It takes 4 inputs (daily energy use in kWh, peak sun hours per day in hours, rated power per panel in W, system performance ratio) and returns the solar panel number. These calculators are for homeowners, renovators, builders, landscapers and tradespeople planning work on a house, yard or site, covering how much material an area will take, how a layout, slope or frame should be set out, and what size or capacity a room, tank or system needs before anything is bought or built. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. Measure the real space rather than working from nominal figures on a plan, and keep every length, area and volume in one unit system before entering it so feet and metres never get mixed. Where the result is material to buy, treat it as a starting figure and round up, because bags, sheets, rolls and panels come in fixed sizes and some of every order goes to offcuts, breakage and second coats; where the result is a dose, load or size rating, use it as calculated rather than padding it. For example, with daily energy use = 10 kWh, peak sun hours per day = 4 hours, rated power per panel = 300 W, system performance ratio = 0.8, the solar panel number works out to 11, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by U.S. Department of Energy: Solar Energy Technologies, and the figure above each result carries the date it was last verified. These are planning figures, not a structural, electrical or safety check. What a job actually consumes shifts with substrate porosity, compaction, ground conditions, waste and each product's own coverage or dose rating, so confirm the final quantity against the product details or with your supplier before ordering, and have any load-bearing, electrical, gas or drainage work designed and checked by a qualified professional.