Home Solar Guide
Solar can be a great investment or a bad one depending on your roof, rates, and incentives. We show you how to tell the difference before you sign anything.
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How Many Solar Panels Do You Need?
Work out how much each panel produces in a year, then divide your annual kWh by that. A panel's yearly output is its wattage ÷ 1,000 × your local peak sun hours × 365, minus system losses — PVWatts uses a 14% default. On that basis a 400W panel at 4.5 sun hours makes roughly 565 kWh a year, so a home using the U.S. average of about 10,800 kWh would need somewhere near 19 panels.
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Is There Still a Federal Solar Tax Credit in 2026?
The federal Residential Clean Energy Credit under IRC §25D is no longer available for residential solar expenditures made after 31 December 2025; Public Law 119-21 ended it early. For solar, an expenditure is generally treated as made when the original installation is completed, so a system finished in 2026 does not qualify — even if you paid for it in 2025. State, local and utility incentives may still apply.
How Fast Do Solar Panels Degrade Over Time?
NREL's compendium of more than 11,000 published degradation rates puts crystalline silicon at a median of 0.5% to 0.6% a year — but a mean of 0.8% to 0.9%, because a minority of systems degrade much faster. Compounded at 0.6% a year, a system holds about 94% of its first-year output after 10 years, 89% after 20 and 86% after 25. NREL also notes that modules are typically warrantied for 20 to 25 years and keep producing afterwards, with no fixed end to their productive life. Two cautions: a performance warranty covers module power under a test, not the kWh your roof produces in a given year; and a sudden double-digit drop is almost never slow annual degradation. That is a fault to diagnose.
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Every figure in this section is a modelled estimate from public data, printed with the assumptions and sources behind it. Read how we build and check these numbers