Solar Panel Degradation Calculator — Project Your System’s Output Over 25 Years

A solar panel degradation calculator projects how much power your solar array will produce each year as panels slowly lose efficiency over time. Enter your system size, first-year production estimate, Year 1 LID rate, and annual decay rate — the calculator returns your total lifetime energy output in MWh, your final-year capacity percentage, whether your panels stay above the manufacturer’s warranty floor, and a full degradation curve visualisation across your chosen analysis horizon.

How to Use the Solar Panel Degradation Calculator

Step 1 — Enter your system profile.

Give your project a name for the PDF export, then enter your total system size in kilowatts — the combined STC nameplate wattage of all panels. A typical US residential system runs between 6 kW and 12 kW. Then enter your estimated Year 1 production in kWh. Your installer’s proposal or a NREL PVWatts estimate for your location and system size gives you this figure. A well-sited 8 kW system in most of the continental US produces roughly 9,600 to 12,800 kWh in its first year depending on climate and shading.

Step 2 — Set the Year 1 LID rate.

Use the slider to enter the Light Induced Degradation rate — the one-time efficiency drop that occurs when panels are first exposed to sunlight. LID is a well-documented semiconductor physics phenomenon where boron-oxygen defects activate in crystalline silicon cells during initial UV exposure. Most standard P-type monocrystalline panels experience a 1.5–3% LID drop. Premium N-type panels (TOPCon, HJT) have virtually zero LID — typically under 0.5%. Check your panel datasheet or warranty document for this figure; if not listed, use 2% as a conservative default for standard monocrystalline panels.

Step 3 — Set the annual degradation rate.

This slider controls the linear decay rate applied from Year 2 onward. The industry standard for Tier 1 monocrystalline panels is 0.5%/year, which is what most major manufacturers including Qcells, LONGi, Canadian Solar, and REC guarantee in their linear power output warranties. Premium N-type and HJT panels from SunPower and Panasonic typically guarantee 0.25–0.30%/year. Budget or older P-type PERC panels may degrade at 0.6–0.8%/year. Find the exact figure in your panel’s power output warranty section under “annual degradation” or “linear warranty rate.”

Step 4 — Set your analysis horizon.

Drag the Warranty Horizon slider to the number of years you want to project — typically 25 years to match the standard US solar panel warranty period, or 30–35 years if you want to model beyond the warranty for a long-term investment analysis. The midpoint and endpoint year labels on the degradation curve chart update automatically to reflect your selected horizon.

Step 5 — Set the manufacturer’s power guarantee.

Enter the minimum capacity percentage your manufacturer guarantees at the end of the warranty period. Most US solar manufacturers guarantee 80–87% of original output at year 25. SunPower guarantees 92% at year 25 under their Maxeon warranty. Standard warranties often guarantee 80–83%. The calculator flags a warning in red if your calculated degradation curve drops below this threshold — meaning your panels would degrade faster than the manufacturer’s guarantee covers.

Step 6 — Read the results.

The Final Array Health banner shows your system’s remaining capacity percentage at the end of your analysis period, in green if it meets or beats the warranty floor and red if it falls below. The Lifetime Output card shows total cumulative energy production in MWh, Year 1 actual yield after LID, final-year yield, and total kilowatt-hours lost to degradation over the system’s life. The degradation curve chart plots your array’s declining capacity year by year as a blue filled area, with the manufacturer’s warranty floor as a dashed orange line — making it immediately visible whether your modelled decay stays above the guarantee.

Step 7 — Export your report.

Click Export PDF to generate a printable degradation analysis report labelled with your project name. Useful for installer comparison documents, financing applications, or long-term energy budget planning.

The Degradation Formula Explained

The calculator uses the standard two-phase linear degradation model used by most US solar manufacturers in their warranty documentation:

Year 1 capacity after LID: Year 1 Capacity = 100% − LID Rate

Year 2 onward (linear): Year N Capacity = Year 1 Capacity − (Annual Degradation Rate × (N − 1))

Annual production at Year N: Year N Production (kWh) = Year 1 Baseline × (Year N Capacity ÷ 100)

Lifetime total: Total MWh = Sum of all annual kWh outputs from Year 1 through Year N

Example: An 8 kW system producing 11,200 kWh in Year 1, with 2% LID and 0.5%/year degradation over 25 years:

• Year 1 actual output = 11,200 × 0.98 = 10,976 kWh
• Year 25 capacity = 98% − (0.5% × 24) = 86%
• Year 25 output = 11,200 × 0.86 = 9,632 kWh
• Total lifetime production ≈ 253 MWh

Frequently Asked Questions

Q: What is solar panel degradation and why does it happen?

A: Solar panel degradation is the gradual decline in power output that occurs as panels age. It happens for several reasons: UV exposure breaks down the anti-reflective coating and encapsulant materials over time; thermal cycling — the daily expansion and contraction between hot afternoons and cool nights — causes microscopic cracks in the silicon cells and solder connections; and moisture ingress slowly degrades the back sheet and cell contacts. The result is a slow, predictable, linear reduction in the amount of electricity the panel can generate from the same amount of sunlight. This degradation is normal, expected, and accounted for in standard US solar panel warranties.

Q: What is the average solar panel degradation rate in the US?

A: According to NREL (National Renewable Energy Laboratory) research analysing data from thousands of US residential systems, the median degradation rate for modern monocrystalline silicon panels is approximately 0.5% per year. Premium N-type panels using TOPCon or heterojunction (HJT) cell technology degrade at around 0.25–0.30%/year. Older polycrystalline panels installed before 2015 often degrade at 0.6–0.8%/year. At 0.5%/year, a panel rated at 400W today will produce approximately 388W in year 7, 370W in year 15, and 350W in year 25 — still 87.5% of its original capacity.

Q: What is LID (Light Induced Degradation) in solar panels?

A: LID is the one-time efficiency drop that occurs when a solar panel is first exposed to sunlight. In standard boron-doped P-type monocrystalline silicon cells, UV light activates boron-oxygen defects in the crystal lattice that create recombination centers — essentially traps that capture electrons before they can contribute to current flow. This activation is permanent and irreversible, and it typically reduces panel output by 1.5–3% during the first few hundred hours of operation. After this initial drop, the panel stabilises and enters its long-term linear degradation phase. Premium N-type cells (used in TOPCon and HJT panels) do not use boron doping and therefore experience virtually zero LID — one of their key advantages over standard P-type technology.

Q: How much power will my solar panels lose after 25 years?

A: With a standard 2% LID plus 0.5%/year linear degradation, your panels will retain approximately 86–88% of their original rated capacity after 25 years. On a 400W panel, that means producing around 344–352W at year 25. With a premium 0.25%/year degradation rate (SunPower Maxeon warranty), year 25 capacity reaches approximately 93–94%. Most US manufacturer warranties guarantee a minimum of 80–87% at year 25, so well-specified panels typically outperform their warranty floor by a meaningful margin. Total lifetime energy lost to degradation over 25 years on a standard 8 kW system typically ranges from 4,000 to 8,000 kWh depending on the degradation rate — use this calculator to find the exact figure for your specific system.

Q: Do solar panels ever stop working completely?

A: No — solar panels do not suddenly stop working; they simply produce progressively less power with each passing year. Most well-manufactured panels continue to generate meaningful electricity well beyond their 25-year warranty period. NREL field studies have found panels from the 1980s and 1990s still operating at 70–80% of their original output. The more common reason systems are decommissioned after 25–30 years is not panel failure but inverter end-of-life or the economic case for repowering with higher-efficiency modern panels rather than any actual cessation of panel operation.

Q: What is the difference between a linear warranty and a tiered warranty for solar panels?

A: A tiered warranty guarantees a specific minimum output at two points — typically 90% at year 10 and 80% at year 25 — but allows the degradation path between those points to be non-linear. A linear warranty, which has become the standard among Tier 1 US manufacturers, guarantees that the panel will not degrade faster than a fixed annual rate (e.g., 0.5%/year) in any given year throughout the warranty period. The linear warranty is superior because it protects against accelerated early degradation — a panel under a tiered warranty could theoretically lose 8% in year 3 and still be within warranty terms, while a linear warranty would cover that loss.

Q: How does solar panel degradation affect my electricity bill savings over time?

A: Because your panels produce progressively less electricity each year, the kilowatt-hours offset against your utility bill also decline annually. In practice, this is largely counteracted by rising electricity rates — most US utilities have historically increased rates 2–4% per year, which offsets the 0.5% annual production decline and then some. The net effect is that your dollar savings from solar typically remain stable or even increase over the first decade despite physical degradation, because the electricity you are avoiding buying becomes more expensive faster than your panels lose output. The degradation calculator quantifies the physical production side of this equation.

Q: Which solar panels have the lowest degradation rate available in the US market?

A: SunPower’s Maxeon panel line currently offers the industry’s best documented long-term degradation performance, with a warranty guaranteeing 92% output at year 25 — implying an effective rate well below 0.3%/year including LID. REC’s Alpha Pure-R (heterojunction technology) guarantees 92% at year 25 as well. Panasonic’s EverVolt HJT line and Canadian Solar’s HiHero TOPCon series both guarantee 87–90% at year 25. Standard Qcells, LONGi, and Canadian Solar monocrystalline panels typically guarantee 84–87% at year 25, consistent with 0.5%/year linear degradation.