Size Your Solar Array,
Offset 100% of Utility Bills.
Free solar calculators: the system size your bill implies, panel count by wattage, payback period with incentives, and how much of your bill solar actually offsets.
Regional Peak Sun Hours
Solar insolation yields vary from 3.5 hours/day in the Pacific Northwest to 6.2 hours/day in the Desert Southwest.
Roof Azimuth & Tilt De-rate
South-facing 180° true azimuth generates 100% output; east/west orientations require 15–20% oversizing.
Battery Storage Sizing
Size home storage (10–13.5 kWh) to cover essential overnight refrigeration, medical devices, and lighting circuits.
SolarSpan Calculators
Solar System Size Calculator
The system size (kW) and panel count that your electric bill implies, based on your sun-hours and target offset.
Solar Payback Calculator
Years to payback and 25-year savings, from system cost, incentives, production, and your rate — with rate-inflation accounted.
Solar Production Estimate
Annual kWh from system size, sun-hours, orientation, and shading — the number your savings math depends on.
Solar Bill Offset Calculator
How much of your annual usage (and bill) a proposed system actually covers — including fixed charges that solar cannot touch.
Technical Reference Guides
Reading a solar quote like an auditor
Five lines on every quote that decide whether it is good — and the three that are decoration.
Batteries: resilience purchase or economics mistake?
When a battery earns its place and when it is a very expensive安全感 purchase.
12 mistakes people make with home solar
The recurring errors we see in home solar — what causes each one, and the habit that prevents it.