Ballpark estimate against final design
What the widget assumes
Monthly bill (USD)
Tariff used to turn the bill into kWh (USD per kWh)
Share of usage to cover (%)
Yield assumed (kWh per kW a year)
Price per watt (USD)
Range either side of the price (%)
What the final design finds
Fixed charges inside the bill (USD a month)
Yield after shading (kWh per kW a year)
Module power (W)
Modules the roof holds (whole number)
Final price per watt (USD)
Adders (USD, one total)
The starting values are the invented inputs on the page, not market data or any vendor's method. Type 1000 or 1,000 for one thousand and 0,2 or 0.2 for a fifth. Entries such as 1.000 and trailing separators are rejected as ambiguous.