A real payback calculation — not the salesperson's optimistic version.
Your real payback period and lifetime savings
Solar payback calculations from installers frequently use optimistic assumptions: maximum sun hours, 100% bill coverage, and the highest applicable incentives. Real-world performance often runs 10-20% below the rosy projections, extending payback periods meaningfully.
The 30% US federal investment tax credit (ITC) is substantial, but it's a tax credit — not a rebate. You need enough tax liability to use it. Homeowners with lower incomes or significant existing deductions sometimes can't fully utilise the credit in a single year.
Battery storage adds significantly to cost but is often presented as part of the same conversation. The ROI on batteries is generally much worse than panels alone — calculate them separately and only add batteries if time-of-use pricing or outage protection is genuinely valuable to you.