Solar Degradation Calculator: PERC, TOPCon, HJT

Solar panels do not produce the same output in year 25 as they do in year one. Every photovoltaic module loses a small fraction of its power each year, and that loss compounds. A 0.55% annual drop sounds minor until you apply it across 25 years and thousands of kilowatt-hours.

This guide is a working solar panel degradation calculator. It shows year-by-year output for three example assumption sets (PERC, TOPCon and HJT), explains why degradation happens and how warranties model it, and sets the results against published field data. The calculator math is exact. The input rates are examples, so replace them with the values on your module’s datasheet.

Last updated: November 2026.

In this guide:

• What solar panel degradation is and why it matters for project finance
• How the first-year loss and the annual rate fit together (the stepped model)
• Year-by-year output formulas with worked examples
• A full 25-year table comparing three example assumption sets
• How temperature, humidity, LID, PID and other failure modes affect output
• What performance warranties promise, and what field studies report
• 25-year versus 30-year projections
• What the degradation gap is worth, and how to test a price premium

Degradation Rates Used in This Calculator

Solar panel degradation is the gradual, irreversible loss of power output over time. It comes from chemical and physical changes in the cell, the encapsulant and the electrical connections. Degradation is not failure: a degraded panel still produces power, just less than when new.

The calculator uses three example assumption sets. They are not the warranty of any specific product. Manufacturers publish their own first-year loss, annual rate and guaranteed output at year 25 or 30, and those terms differ by brand and product line.

Year-25 values are calculated with the stepped formula in this guide. Rates are example assumptions; check the datasheet of the module you are pricing.

The gap between the PERC-style and HJT-style cases at year 25 is 5.8 percentage points of rated output. On a 500 kW system, that gap is about 29 kW of capacity.

What Is Solar Panel Degradation and Why It Matters

Degradation has several causes that operate at the same time and at different speeds.

Cell-level effects. Crystal defects, light-induced defects and metallization changes reduce the current a cell can deliver. Solder bonds between cell and ribbon can fatigue under thermal cycling.

Encapsulant effects. The polymer that seals the cells can yellow or brown under UV and heat, which cuts the light reaching the cell. Material choice matters here, so check the module’s encapsulant and backsheet or glass-glass construction.

Electrical effects. Busbars, connectors and junction boxes can corrode in humid environments, and bypass diode failures reduce string output.

Mechanical effects. Frame seal degradation lets moisture in, and microcracks can spread under thermal cycling and wind loading, more often in poorly manufactured units.

Why Degradation Matters for Project Economics

A financial model assumes a certain output in year one and a certain decline after that. If actual degradation exceeds the modeled rate, the project underperforms. Debt service coverage falls, equity returns shrink and PPA offtakers receive less energy than contracted. The effect is small each year and large across a 25-year contract.

Design and financial tools should model degradation as a stepped curve with technology-specific inputs, not as one flat percentage for every module. A solar design platform that lets you set the first-year and annual rates separately gives a more defensible projection than a flat 0.5% applied to everything.

Degradation Rates by Cell Technology

Cell architecture, dopant type and metallization all affect long-term stability. Datasheets give the numbers that apply to a specific module; the notes below explain the differences you will see.

PERC (Passivated Emitter and Rear Cell)

PERC adds a dielectric passivation layer to the rear of a standard cell to cut recombination. Most PERC modules use boron-doped p-type silicon, which can show light-induced degradation (LID) from boron-oxygen complexes in early exposure. That is why PERC warranties often state a larger first-year loss than n-type products. Some PERC cells can also show light and elevated temperature induced degradation (LeTID), which manufacturers address through process changes. Check the module’s LID and LeTID test results.

What most installers get wrong: they treat the annual rate as the whole story. The first-year loss in the PERC-style example is 2%, which is almost four times the 0.55% annual rate. A model that applies 0.55% from year one overstates lifetime production slightly, as the linear-model section below shows.

TOPCon (Tunnel Oxide Passivated Contact)

TOPCon is an n-type cell design with an ultra-thin tunnel oxide and a polysilicon contact on the rear. N-type silicon avoids the boron-oxygen LID mechanism, and many TOPCon warranties state lower first-year and annual losses than comparable PERC products. TOPCon cells are often bifacial; see our bifacial solar panel design guide for how rear-side gain is modeled.

HJT (Heterojunction Technology)

HJT combines crystalline silicon with thin amorphous silicon layers, which reduces surface recombination. Many HJT datasheets state a low annual degradation rate and a low temperature coefficient, which can help in hot climates. HJT modules have typically carried a price premium over PERC and TOPCon, so compare the lifetime value of the lower rates against the actual quoted price difference.

Thin-Film (CdTe)

Thin-film CdTe modules are the main non-silicon technology in utility-scale use. They do not use ribbon solder bonds or boron-doped silicon, and their warranties state their own first-year and annual rates. Read the manufacturer’s current datasheet for those terms.

Technology Comparison Summary

Year 1 vs. Annual Degradation: Linear vs. Stepped Models

Financial models use two approaches to degradation: linear and stepped. The choice shifts lifetime production estimates by a small percentage.

The Stepped Model (Preferred)

The stepped model applies a first-year loss, then a lower constant rate for later years. It matches how warranties are written for most modern modules.

Formula:

Year 1 output = P rated × (1 − d1)
Year n output = Year 1 output × (1 − dannual)^(n−1)

Where:

• P rated = nameplate power (W)
• d1 = first-year degradation rate (decimal)
• dannual = annual degradation rate for years 2 onward (decimal)
• n = year number

Example: 10 kW PERC-style system (2.0% then 0.55%)

Year 1: 10,000 W × (1 − 0.02) = 9,800 W
Year 2: 9,800 W × (1 − 0.0055) = 9,746 W
Year 5: 9,800 W × (1 − 0.0055)^4 = 9,586 W
Year 10: 9,800 W × (1 − 0.0055)^9 = 9,325 W
Year 25: 9,800 W × (1 − 0.0055)^24 = 8,585 W

The Linear Model (Simpler, Slightly Optimistic)

The linear model applies the same annual rate from the start and misses the larger first-year loss.

Example: 10 kW PERC-style system, annual rate only

Year 1: 10,000 W × (1 − 0.0055) = 9,945 W  (145 W above the stepped value)
Year 25: 10,000 W × (1 − 0.0055)^25 = 8,694 W  (109 W above the stepped value)

At 1,500 kWh per kW per year, the annual-rate-only model overstates 25-year production by about 5,093 kWh for this system, roughly 1.5%. At an assumed $0.15 per kWh, that is about $764 of phantom revenue.

How to Calculate Year-by-Year Output

Here is the complete method for any system size and technology.

Step 1: Identify Your Parameters

Specific yield depends on location. Use PVGIS, NREL PVWatts or site-specific irradiance data. The 1,500 kWh per kW per year used here is an example, not a forecast for any site.

Step 2: Calculate Year-One Output

Year 1 energy = 10 kW × 1,500 kWh/kW × (1 − 0.02) = 14,700 kWh

Step 3: Calculate Each Subsequent Year

Year n energy = Year 1 energy × (1 − 0.0055)^(n−1)

Example for year 10:

Year 10 energy = 14,700 × (1 − 0.0055)^9 = 13,988 kWh

Step 4: Sum for Lifetime Production

Lifetime production = Year 1 × [1 + (1−d) + (1−d)^2 + ... + (1−d)^24]

For the PERC-style case at 0.55% annual loss, the bracket sums to about 23.42:

Lifetime production = 14,700 × 23.42 = 344,238 kWh

Step 5: Calculate Cumulative Revenue

Cumulative value = Lifetime production × $/kWh
= 344,238 × $0.15 = $51,636

Step 6: Compare Technologies

These gaps are undiscounted and exclude any difference in module price, which the next sections cover.

Degradation Calculator: 25-Year Table for a 10 kW System

The table shows year-by-year energy for a 10 kW system with a specific yield of 1,500 kWh per kW per year. Output is shown before inverter, soiling and shading losses, so treat it as a degradation-only view.

Year-by-Year Degradation: PERC, TOPCon and HJT Examples

Totals sum years 1 to 25 and are rounded to the nearest kWh. Specific yield of 1,500 kWh per kW per year is assumed. Actual output varies by location, orientation, tilt and shading. A shadow analysis shows shading losses before installation.

Cumulative Production Comparison

Both prices are assumptions, not market data. The lower price shows how a cheaper kWh shrinks the dollar gap between technologies.

Temperature and Climate Impact on Degradation

Degradation does not happen at the same speed everywhere. Heat, humidity and thermal cycling all speed up the processes behind it.

How Temperature Accelerates Degradation

Chemical and mechanical aging processes run faster at higher temperatures, which is why hot, humid sites tend to report higher loss rates. Module operating temperature sits well above ambient in full sun, so a hot desert site can push cells much hotter than a cool temperate site. This guide does not publish a climate multiplier table, because a reliable one needs a named source and your module’s test data. Instead, test a conservative case.

Practical approach: run your base case with the datasheet rates, then run a sensitivity case with a higher annual rate (for example, double the warranted annual rate) for hot or humid sites. If the project still works, the margin is real.

Temperature Coefficient: A Separate Effect

Temperature also lowers power instantly through the module’s temperature coefficient. That is a reversible, day-to-day loss and not degradation, but it matters for the same hot sites. As an illustration with assumed coefficients, a module with a -0.38%/°C coefficient at 70°C cell temperature loses (70 − 25) × 0.38% = 17.1% of rated power to heat, while one with -0.25%/°C loses (70 − 25) × 0.25% = 11.3%. Read the actual Pmax coefficient on each datasheet.

Humidity and Precipitation Effects

Humidity drives three mechanisms:

PID (potential induced degradation). High humidity plus high system voltage can drive ion migration and leakage currents in the module. It can be reversible in its early stages.

Encapsulant hydrolysis. Moisture can break down some encapsulant materials, causing delamination and optical loss.

Corrosion. Frames, junction boxes and connectors corrode in salty or humid air. Coastal installations need appropriate protection.

For related reading, see our guides to PID and LID and LeTID.

PID, LID and Other Failure Modes

Knowing the failure mode helps separate reversible from irreversible losses.

LID (Light Induced Degradation)

LID mainly affects boron-doped p-type silicon such as many PERC cells. When the cell is first exposed to light, boron and oxygen form complexes that act as recombination centers, which reduces the current the cell can deliver.

• It happens in the first hours to weeks of operation.
• It is largely complete by commissioning, so it shows up as lower initial output, not ongoing decline.
• It does not affect n-type cells in the same way.
• Gallium-doped p-type cells were developed to reduce it.

PID (Potential Induced Degradation)

PID is a voltage-driven effect. In arrays with high string voltages, the electric field can drive ions through the front glass and encapsulant toward the cell, creating shunt paths that bypass the junction.

• It can affect crystalline silicon technologies.
• It is worse in hot, humid conditions.
• It can be reversible in early stages with proper grounding and voltage management.

Prevention: use modules with PID test results, ground the system correctly, consider PID recovery devices where the design calls for them, and manage string voltages.

LeTID (Light and Elevated Temperature Induced Degradation)

LeTID is a slower mechanism that appears under light and elevated temperature in some PERC cell designs. It is specific to certain cell designs and not every PERC module shows it. Check the manufacturer’s LeTID test results.

Solder Bond Fatigue

Daily temperature swings cause differential expansion between silicon cells and copper ribbons. Over thousands of cycles, solder bonds can crack and series resistance can rise, gradually reducing power. Climates with large daily temperature ranges stress these bonds more. Multi-busbar and shingled designs change the stress pattern, so ask the manufacturer for its thermal cycling results.

Backsheet Degradation

The rear polymer sheet protects cells from moisture and provides electrical insulation. Cracking, yellowing or chalking on the rear surface can signal backsheet degradation and a safety risk. Glass-glass modules do not use a polymer backsheet.

Warranty Terms: What Manufacturers Promise

Solar panel warranties have two parts, and they are not the same thing.

Product Warranty

The product warranty covers physical defects such as delamination, frame corrosion, junction box failure, bypass diode failure and cell cracking. The term differs by manufacturer and product line, so read the warranty document for the module you are buying.

Performance Warranty

The performance warranty guarantees a minimum power output at stated years. Most modern warranties are written as a linear schedule: a guaranteed output at the end of year one, then a stated loss per year to the end of the warranty term.

For illustration only, a linear warranty with a 1% first-year loss and 0.40% per year afterward guarantees about 100 − 1 − (0.40 × 24) = 89.4% at year 25. The stepped model compounds the annual rate on a shrinking base, so its year-25 figure sits slightly above a linear warranty with the same inputs. Compare your model’s output against the datasheet’s guaranteed value, not only against the rate.

What the Warranty Actually Means

A performance warranty means the manufacturer guarantees the panel will produce at least the stated percentage of its rated power at the stated year. If a panel falls below that line, the buyer can make a claim under the warranty terms.

What a warranty typically does not cover:

• Degradation beyond the warranty term
• Power loss from soiling, shading or inverter failure
• Damage from improper installation
• Degradation faster than warranted, unless you can document it

The claims process: A claim usually needs documented power measurements under standard test conditions. Many installers do not have the equipment to measure that in the field, which makes claims harder to file in practice. Read the claim procedure before you buy.

For a side-by-side look at published terms, see our solar panel warranty comparison and solar panel degradation rates guide.

25-Year vs. 30-Year Output Projections

Most project models use a 25-year life, but many systems will keep operating longer. Extending the horizon shows how the gap between technologies grows.

30-Year Output Projection (10 kW System)

The HJT-style advantage grows from 3.5% at 25 years to 4.2% at 30 years. Low annual degradation compounds its lead.

Should You Model 30 Years?

For most projects, 25 years is the right horizon, because it matches:

• standard PPA terms
• debt financing tenors
• common manufacturer warranty periods
• investor return targets

Model 30 years when the project has a 30-year PPA or lease, when the offtaker asks for long-term estimates, or when you are comparing technologies for assets that will run beyond year 25.

What the Degradation Gap Is Worth

Degradation affects the metrics investors track, such as lifetime energy, levelized cost of energy (LCOE) and IRR. This guide stops at lifetime energy and value, because the LCOE and IRR results depend on your CAPEX, financing, O&M and discount rate, which this guide cannot assume for you.

Using the examples above, the extra 25-year energy relative to the PERC-style case is:

How to use the last column: it is the most a module price premium could be worth, in dollars per watt, before discounting, under these assumptions. If a quote adds more per watt than the figure, the degradation advantage alone does not pay for it. Discounting lowers the break-even further, because the extra energy arrives late.

For the full picture, enter your own capital cost, O&M, tariff and discount rate in the generation and financial tool and compare net present value, not only energy.

Why Degradation Matters Less Than Installers Think

Degradation is important, but it is rarely the decisive factor in technology selection.

The Numbers Are Smaller Than They Look

A 0.55% versus 0.30% annual rate difference sounds large. In annual terms the difference is 0.25 percentage points, which is about 37.5 kWh per year on a 10 kW system at 1,500 kWh per kW. At $0.15 per kWh, that is about $5.62 a year in the first years. Over 25 years the gap builds, as the table above shows, but it stays modest against the other inputs in the model.

What Can Justify a Low-Degradation Module

A lower degradation rate makes more sense when:

• space is constrained, so higher efficiency means more kW per square meter
• operating temperatures are high, so the temperature coefficient also matters
• the project has 30-year financing or a long PPA
• the buyer values the warranty term and the manufacturer’s financial strength
• bifacial gain is significant for the site

The degradation rate alone is one factor in a multi-variable decision.

What Most Installers Get Wrong

Installers often overstate or understate degradation because they:

1. use a linear model instead of a stepped model
2. copy one climate-agnostic rate into every project
3. compare technologies on degradation alone, not on total system value
4. skip the sensitivity case for hot or humid sites

A better approach is to model each option with stepped degradation, a sensitivity case and full CAPEX and OPEX, and let the net present value decide.

Real-World Degradation Data from Field Studies

Warranty documents and laboratory tests tell one story. Field data adds another, and its main lesson is that results vary by system and by method.

Jordan and Kurtz, NREL (2012)

Dirk Jordan and Sarah Kurtz of NREL assembled nearly 2,000 degradation rates from the literature, measured on individual modules or entire systems over about 40 years of field testing. The review reports a median of 0.5% per year. See the Photovoltaic Degradation Rates: An Analytical Review abstract. The sample includes older module designs, so it describes the historical field record and not any new product.

IEA PVPS Task 13 (2021)

The IEA PVPS Task 13 report Assessment of Performance Loss Rate of PV Power Systems benchmarks the methods used to calculate performance loss rates (PLR). Of the 19 research systems it studied, nine had PLR values between -0.4% and -1% per year, three had smaller losses and six had larger losses, in the range of -1% to -4% per year. The report also finds that the calculation method and the data quality change the result, so compare PLR figures only when they use the same method.

What the Field Data Means for a Model

• A median near 0.5% per year is a reasonable reference point for a base case, but the spread is wide.
• A system with a quality problem can lose far more than the median, which is why supplier selection, installation quality and monitoring matter.
• Warranty rates and field results are not the same quantity. Compare like with like, and keep monitoring data so you can check a real system against its model.

How to Use This Calculator for Your Project

Step 1: Gather Inputs

Step 2: Build the Year-by-Year Table

Use the stepped model formula:

Year 1 = Rated × (1 − d1) × Specific Yield
Year n = Year 1 × (1 − dannual)^(n−1)

Step 3: Calculate Cumulative Production and Revenue

Sum the annual production and multiply by electricity value. Apply discounting if you are calculating NPV.

Step 4: Compare Technologies on Total Value

Do not compare on degradation rate alone. Compare on:

• total lifetime production
• total lifetime revenue
• net present value at the project discount rate
• quoted module price difference per watt

Step 5: Run a Sensitivity Case

For a hot or humid site, rerun the table with a higher annual rate and see whether the project still meets its return target.

Conclusion

Solar panel degradation is real and measurable, and the math is simple. The inputs are the hard part, because they come from datasheets and field experience that differ by product and site.

What to remember:

1. Use the stepped model. Enter the first-year loss separately from the annual rate and do not apply a flat rate from year zero.
2. Take rates from the datasheet. The PERC-style, TOPCon-style and HJT-style sets in this guide are examples only.
3. Check the price premium per watt. The extra 25-year energy from a lower-degradation module has a ceiling value; compare it with the quoted premium.
4. Test a harsher case for hot or humid sites. Field results vary widely, so a sensitivity run is cheap insurance.
5. Treat degradation as one variable. Specific yield, orientation and procurement price often move the result more.

To build a stepped degradation curve into a real proposal, book a SurgePV demo and bring a project with your module’s datasheet rates. If cost is your first question, see the SurgePV pricing page.

Frequently Asked Questions

What is the solar panel degradation rate by technology?

It depends on the module, so read the datasheet. NREL’s Jordan and Kurtz review of nearly 2,000 field rates found a median of 0.5% per year. This guide’s examples use 2% then 0.55% per year (PERC-style), 1% then 0.40% (TOPCon-style) and 1.5% then 0.30% (HJT-style), which are assumptions and not any product’s warranty.

How do you calculate solar panel degradation year by year?

Use the stepped model: year 1 output equals rated power times (1 minus the first-year loss), and each later year equals the prior year times (1 minus the annual rate). For a 10 kW system at 2% then 0.55%, year 1 is 9,800 W, year 2 is 9,746 W and year 25 is 8,585 W.

What does a 25-year solar panel warranty actually cover?

A performance warranty guarantees a minimum percentage of rated power at stated years, usually as a linear schedule on the datasheet. A product warranty covers physical defects and is separate. Claims usually need documented power measurements, so read the claim procedure before you buy.

How does temperature affect solar panel degradation?

Heat and humidity speed up the chemical and mechanical processes behind degradation, so hot, humid sites tend to report higher loss rates. Temperature also cuts power instantly through the temperature coefficient, which is a separate and reversible effect. For hot sites, run a sensitivity case with a higher annual rate.

What is the difference between LID and PID in solar panels?

LID is light-induced degradation, linked to boron-oxygen defects in p-type silicon and mostly complete soon after commissioning. PID is potential-induced degradation, a voltage-driven loss that is worse in hot, humid conditions and can be reversible early on. Check the datasheet for LID and PID test results; IEC 62804 covers PID testing.

Do solar panels really last 25 years?

Many modules keep producing beyond 25 years, but the 25-year figure is a warranty term and not a lifespan guarantee. Field results vary: the IEA PVPS Task 13 benchmarking study found nine of 19 research systems between -0.4% and -1% per year and six between -1% and -4%. Monitoring shows how your own system is behaving.

How much money does solar degradation cost over 25 years?

It depends on the rates, yield and tariff. For a 10 kW system at 1,500 kWh per kW and an assumed $0.15 per kWh, the example sets lose about $2,800 (HJT-style) to $4,600 (PERC-style) of energy value over 25 years compared with a system that never degraded. Replace the assumptions with your own.