Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Projected production at chosen year
10,640
Percent of original output remaining
88.7%
Meets warranty floor? (1=yes)
1
Cumulative production through that year
282,671
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How to use this
- 1Enter year 1 annual production (kWh).
- 2Enter annual degradation rate (%).
- 3Enter check output at year.
- 4Enter manufacturer warranty floor at that year (%).
- 5Read your projected production at chosen year on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Solar panels don't produce the same output forever — silicon degrades slowly from UV exposure, thermal cycling, and micro-cracking, typically 0.3-0.8% per year depending on panel quality and manufacturer. Most warranties guarantee 90-92% of original output at year 10 and 80-85% at year 25. This calculator projects year-by-year output decline from a chosen first-year production and degradation rate, and checks whether your production stays above your manufacturer's warranty floor across the panel's life — useful for verifying a quote's long-term production claims or estimating output on an existing system you're evaluating for a home purchase.
Worked example
Using the values the calculator loads with:
Inputs
- Year 1 annual production: 12000 kWh
- Annual degradation rate: 0.5 %
- Check output at year: 25
- Manufacturer warranty floor at that year: 85 %
Results
- Projected production at chosen year: 10,640
- Percent of original output remaining: 88.7%
- Meets warranty floor? (1=yes): 1
- Cumulative production through that year: 282,671
What each field means
Inputs
- Year 1 annual production (kWh)
- The year 1 annual production used in the calculation, measured in kWh. Starts at 12000 kWh so you have a working example on load.
- Annual degradation rate (%)
- The annual degradation rate used in the calculation, measured in %. Starts at 0.5 % so you have a working example on load. Accepted range: 0.1–1.5 %.
- Check output at year
- The check output at year used in the calculation. Starts at 25 so you have a working example on load. Accepted range: 1–30.
- Manufacturer warranty floor at that year (%)
- The manufacturer warranty floor at that year used in the calculation, measured in %. Starts at 85 % so you have a working example on load. Accepted range: 50–100 %.
Results
- Projected production at chosen year
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Percent of original output remaining
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Meets warranty floor? (1=yes)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cumulative production through that year
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What degradation rate should I actually expect?
Tier-1 monocrystalline panels from major manufacturers (REC, Qcells, Panasonic, LG while it existed) typically run 0.3-0.5% annual degradation; budget or older polycrystalline panels can run 0.7-1%+. NREL field studies of real installed systems found a median around 0.5-0.6% annually across a wide range of panel ages and types.
How is the warranty floor different from the degradation rate?
The warranty floor (e.g., '85% of original output guaranteed at year 25') is a legal minimum the manufacturer will replace or credit panels for if not met; the actual degradation rate that panels experience in the field is usually better than the conservative number baked into the warranty terms, so most systems outperform their warranty floor throughout their life.
Does degradation happen at a steady rate every year?
Not quite — many panels show a slightly higher 'initial light-induced degradation' (LID) of 1-3% in the first few months of exposure, then settle into the steady linear annual rate this calculator models. Some newer panel technologies (PERC, TOPCon) have reduced this initial LID step significantly.
Should I worry about a system's output at year 25?
Not usually cause for alarm — even at 85% of original output, a well-sized system installed for 100% offset in year 1 is still covering roughly 85% of your usage 25 years later, and most panels continue producing usable power well past their 25-year warranty period, just below the guaranteed floor.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Solar Panel Degradation Over 25 Years Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/panel-degradation-25yr
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/panel-degradation-25yr" target="_blank" rel="noopener">Solar Panel Degradation Over 25 Years Calculator — RevenueLab</a> (2026).</p>
Source: [Solar Panel Degradation Over 25 Years Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/panel-degradation-25yr) (2026).