Production-retention milestones
Both scenarios start from the same entered Year 1 production so the table isolates only the effect of the degradation rate.
| Year | Primary production | Primary retention | Comparison production | Comparison retention |
|---|---|---|---|---|
| Year 1 | 12,000 kWh | 100.0% | 12,000 kWh | 100.0% |
| Year 5 | 11,762 kWh | 98.0% | 11,880 kWh | 99.0% |
| Year 10 | 11,471 kWh | 95.6% | 11,733 kWh | 97.8% |
| Year 15 | 11,187 kWh | 93.2% | 11,587 kWh | 96.6% |
| Year 20 | 10,910 kWh | 90.9% | 11,443 kWh | 95.4% |
| Year 25 | 10,640 kWh | 88.7% | 11,300 kWh | 94.2% |
Review notes
- The model starts from the entered Year 1 production and applies 0.50% degradation to each following year. It does not apply a separate first-year warranty step-down.
- A panel performance warranty is a contractual power-retention floor under stated conditions, not a guarantee of annual household kWh. Use the manufacturer's actual warranty schedule when reviewing a specific module.
- Weather, soiling, shading changes, inverter aging, clipping, outages, curtailment, snow and other operating conditions are outside this degradation-only sensitivity model.
- The 0.25% comparison rate is an independent sensitivity scenario using the same Year 1 production, not a claim that one panel will actually outperform another by the modeled amount.
What this calculator is modeling
The entered Year 1 production is treated as the starting point. Beginning in Year 2, the model reduces the previous year's production by the entered annual degradation percentage. The percentage compounds rather than subtracting the same fixed number of kWh every year.
This makes it useful for comparing long-term sensitivity scenarios such as 0.25% versus 0.50% annual degradation without changing the Year 1 production assumption.
Performance warranty is not the same as annual kWh
A module performance warranty usually describes a retained-power floor under specified warranty conditions. It does not promise that a home will produce a fixed number of kilowatt-hours in a future year.
Manufacturer warranty schedules can also include a larger first-year step-down followed by a different annual degradation allowance. This calculator deliberately starts from the entered Year 1 production and therefore does not add a separate first-year warranty loss.
Why actual production can differ from the degradation curve
Annual production changes for many reasons besides module degradation. Weather, shading changes, soiling, snow, inverter availability, clipping, curtailment, equipment outages and maintenance can all move real-world production above or below a simple degradation-only path.
Use this tool to isolate one assumption. Use PVWatts or another site-specific production model when you need a broader production reference.
How to use the comparison rate
The comparison field is useful when two proposals or panel warranties imply different long-term degradation paths. Both scenarios intentionally begin with the same Year 1 kWh so the cumulative difference reflects only the degradation-rate assumption.
A higher modeled lifetime total does not by itself make one panel or proposal better. Installed price, inverter design, roof conditions, warranty terms, equipment availability and installer quality still matter.
Solar Panel Degradation Calculator FAQ
What is the difference between 0.25% and 0.50% annual solar panel degradation?
A lower annual degradation rate preserves more of the entered Year 1 production each following year. Because the reduction compounds, a small annual difference can create a larger cumulative-kWh difference over 20, 25 or 30 years. The calculator lets you put both rates on the same Year 1 starting point so only the degradation assumption changes.
Does a solar panel performance warranty guarantee annual kWh production?
No. A performance warranty generally describes a retained module-power floor under the warranty's stated conditions. Annual household kWh also depends on weather, shading, soiling, inverter operation, clipping, outages, curtailment, snow and other site and operating factors.
Does this calculator include a first-year solar panel degradation step-down?
No. The entered Year 1 production is treated as the starting point, and the annual degradation rate is applied beginning with Year 2. If a manufacturer warranty has a separate first-year allowance and then another annual rate, review that warranty schedule directly instead of treating this calculator as a warranty interpretation.
Is solar panel degradation compounded each year?
In this calculator, yes. Each year's production is calculated from the prior retained fraction, so a 0.50% annual degradation assumption does not subtract the same fixed number of kWh every year. It applies the percentage to the declining production path.
Is the Solar Panel Degradation Calculator a long-term production forecast?
No. It is a degradation-only sensitivity model. It holds the Year 1 production starting point fixed and isolates the effect of the selected degradation rate. It does not forecast future weather, equipment availability, shading changes, maintenance, grid curtailment or other operating conditions.