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Solar System Degradation & 20-Year ROI Calculator

Year 20 total yield

211,680kWh

20-yr sum · yr 20 alone 9,990 kWh (89.2% of new)

Break-even year

10.3yr

Install $18,000.00 recovered from bill savings

Total 20-year savings

$39,582.00

Your total 20-year savings comes out to about $39,582.00.

Inflation on $/kWh · 89.2% of year-1 output in yr 20

20-year production vs. cumulative savings
11.2k$40k15101520Year
  • Energy production (annual kWh)
  • Total savings (cumulative)

Year 20: 9,990 kWh · 39,582 saved cumulatively

Degradation & manufacturer warranty

Tier-1 modules typically lose about 0.5–0.8% per year of output (compound). Warranties often guarantee 80–85% of rated power at 25 years—your modeled year-25 retention at this %/yr is about 86.6%.

Rising retail rates partially offset lower kWh; this calculator applies your energy inflation % to each year's savings while production declines.

Simple solar payback (without year-by-year degradation)

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How this calculator works

How to use the Solar System Degradation & 20-Year ROI Calculator

The Formula

Year-1 kWh = kWp × site yield. Each year output = prior × (1 − degradation %). Savings = kWh × escalating $/kWh. Break-even is when cumulative savings repay installed cost.

Practical Example

The line chart shows falling annual production (amber) vs. rising cumulative bill savings (green)—degradation vs. inflation working in opposite directions.

About Solar System Degradation & 20-Year ROI Calculator

20-year cashflow model

Year-1 kWh = kWp × site yield. Each year output = prior × (1 − degradation %). Savings = kWh × escalating $/kWh. Break-even is when cumulative savings repay installed cost.

Chart

The line chart shows falling annual production (amber) vs. rising cumulative bill savings (green)—degradation vs. inflation working in opposite directions.

Frequently asked questions

Q: Include incentives? A: Enter net installed cost after tax credits. Q: vs. simple payback? A: Solar Payback ROI ignores degradation—use both. Q: Warranty 80% at 25 yr? A: Compare to warrantyCompare in the learn section.

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