How the calculation works
Price per 100 Wp = price ÷ (Wp of one module × modules) × 100
A worked example
Two 440 Wp modules at €179 make 880 Wp: €0.2034 per Wp, or €20.34 per 100 Wp. A balcony set with the same modules and an 800 W inverter at €299 costs €33.98 per 100 Wp — the inverter is part of the price, never of the watt-peak.
Count the modules, not the inverter
A balcony set sold as "800W" usually carries 820–900 Wp of modules behind an 800 W inverter, and a "2000W" set four 500 Wp modules behind the same inverter. Enter the modules' watt-peak: the inverter's watts never make a set cheaper per watt-peak.
Why price per watt-peak
Watt-peak at standard test conditions (STC) is the one figure every label states, so it puts a 100 W foldable panel, a 440 W glass module and a two-module set on the same scale. Compare like with like: a set includes an inverter and cables, a foldable panel a bag and a charger, so both cost more per watt-peak than a bare module.
Common questions
What is a good price per watt-peak?
It moves with the market. Bare glass modules have sold for well under €0.30 per Wp in Germany, balcony sets for €0.30–0.50 per Wp of their modules, and foldable panels for €1 or more per Wp. The catalog shows today's figures per storefront.
Does bifacial count double?
No. A bifacial module also collects light on its back, but its STC rating is the front side; "up to 550 W" figures include rear gain that depends on the ground below. Enter the STC rating.
Is a cheaper watt-peak always better?
Only between comparable products. Check the warranty, the module's certificates and the delivery: large modules can ship by freight, which a listing may charge separately.
Method: arithmetic from the label values you enter. Reviewed .