How to model payback honestly — sun hours, utility rate, escalation and net-metering policy all matter more than sticker price.
The honest formula
Payback = net cost ÷ year-one savings, adjusted for annual utility rate escalation (2–4% is typical). Most U.S. homes land between 7 and 12 years — outliers on either end usually mean a policy or sizing mistake.
What kills payback
Oversizing under net billing, financing at 8%+ APR with dealer fees, or picking an installer whose bid is 30% above local benchmarks. Get three vetted quotes.