PVsyst Degradation Modeling — LID, PID, LeTID and P90 Yield Impact

A solar module shipped from the factory at 550 Wp nameplate will not produce 550 Wp after 25 years. The permanent, progressive loss of power output over a module’s life is degradation — and modeling it accurately in PVsyst is one of the most consequential decisions in a bankable energy yield simulation. At 0.5%/year degradation, a 50 MW project produces 11.1% less energy in Year 25 than Year 1. At 0.7%/year, it produces 15.9% less. That 4.8% difference in Year 25 production represents approximately ₹2–3 crore/year in revenue for a 50 MW Indian project — compounding to ₹30–50 crore in discounted value over the 25-year PPA term.

The degradation question in PVsyst has become more complex as module technology has diversified. Standard p-type PERC modules degrade at 0.4–0.5%/year after Light-Induced Degradation (LID) stabilization. N-type TOPCon modules show 0.3–0.4%/year. HJT modules show 0.2–0.4%/year. And the mechanisms themselves — LID, LeTID (Light and Elevated Temperature Induced Degradation), PID (Potential-Induced Degradation) — vary significantly by technology, operating condition, and manufacturing quality. Choosing the wrong degradation model inflates or deflates the 25-year P90 yield estimate used in financial model debt sizing.

Direct answer. PVsyst models module degradation as an annual rate applied across the 25-year simulation period, with LID (Light-Induced Degradation) applied as a separate Year 1 loss. Standard p-type PERC monocrystalline modules use 0.4–0.5%/year degradation after LID, with 1.0–2.0% LID in Year 1. N-type TOPCon uses 0.3–0.4%/year with negligible LID. PID (Potential-Induced Degradation) is configured as an additional loss category when string voltage or module design presents PID risk. For IREDA and IFC-financed projects, the degradation assumption must be referenced to manufacturer warranty and/or published performance data from peer-reviewed studies.

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Degradation Mechanisms — LID, LeTID, and PID Defined

Understanding which mechanisms apply to a specific module technology is the prerequisite for setting the correct PVsyst degradation parameters.

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Module Technology Degradation Comparison

Module Technology	LID	LeTID	Annual Degradation (post-LID)	Notes
p-type mono PERC (standard)	1.0–2.0%	1.5–5.0% (hot climate risk)	0.40–0.50%/yr	Dominant technology 2020–2024; LeTID risk varies by supplier
p-type mono PERC (LID-free treated)	0.2–0.5%	Reduced but not eliminated	0.40–0.45%/yr	Regeneration treatment applied in manufacturing; marginally better
N-type TOPCon (standard)	0.0–0.2%	Negligible	0.30–0.40%/yr	Boron-free base; no B-O mechanism; LeTID mechanism absent
N-type TOPCon (premium)	0.0–0.1%	Negligible	0.25–0.35%/yr	Premium n-type supply; lower observed degradation in field data
HJT (heterojunction, e.g. Panasonic, REC Alpha, Huasun)	0.0–0.1%	Negligible	0.20–0.30%/yr	Amorphous silicon passivation; lowest degradation; best long-term yield
p-type bifacial PERC	1.0–2.0%	Same as PERC	0.40–0.50%/yr	Bifacial does not affect degradation mechanism; applies to rear as well
N-type bifacial TOPCon	0.0–0.2%	Negligible	0.30–0.40%/yr	Best of both: bifacial gain + low degradation

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Configuring Degradation in PVsyst

PVsyst handles degradation in two separate locations — one for LID and one for annual degradation.

LID Configuration

LID is configured under: System → Module Properties → LID (Light Induced Degradation)

PVsyst applies LID as a Year 1 power loss on top of the nominal module nameplate:

• p-type PERC: enter 1.5% (typical mid-range; adjust based on manufacturer LID test data)
• TOPCon/HJT: enter 0.0–0.2%
• If the manufacturer provides a specific LID test report with measured values, use those values instead of generic estimates

The LID input in PVsyst reduces the effective nameplate power for Year 1. For the simulation, PVsyst applies LID as an instantaneous loss at the start of operation — the simulated Year 1 output reflects the stabilized (post-LID) module performance.

Annual Degradation Configuration

Annual degradation is configured under: System → Module Properties → Annual Degradation

Enter the annual percentage decline in module Pmax. PVsyst applies this degradation compounding across Years 2–25 (or the simulation period set). The cumulative degradation after Y years:

P_Y = P_1 × (1 − d)^(Y−1)

where d is the annual degradation rate (as a fraction, not percent) and P_1 is the post-LID Year 1 power.

Cumulative Yield Impact of Degradation Rate over 25 Years:

Annual Degradation Rate	Year 25 Output vs Year 1	25-yr Average vs Year 1	Life Comparison to 0.5%/yr (relative)
0.20%/yr (HJT)	95.3%	97.6%	+5.0% life yield
0.30%/yr (TOPCon premium)	93.0%	96.4%	+3.6% life yield
0.40%/yr (TOPCon standard)	90.8%	95.3%	+2.4% life yield
0.50%/yr (PERC standard)	88.6%	94.2%	Baseline
0.60%/yr (PERC conservative)	86.5%	93.1%	−1.2% life yield
0.70%/yr (PERC worst case)	84.4%	91.9%	−2.4% life yield

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PID Modeling in PVsyst

PID is configured as an additional loss category under: System → Module Array Losses → PID

PVsyst offers two approaches to PID modeling:

1. Empirical annual PID loss fraction — a percentage entered directly as an estimated annual PID loss
2. Physics-based PID model — using string voltage, module temperature, humidity, and module PID susceptibility parameters

For a bankable IEA, one of two approaches is appropriate:

• If the module is certified as PID-resistant (IEC 62804 tested with satisfactory result and manufacturer declaration), enter 0% PID loss with the certification reference
• If the module has no PID certification or is used in high-voltage configurations (1,000V+ string voltage in hot-humid climates), apply an empirical PID loss of 0.5–2.0% with justification

PID Risk Assessment by Configuration:

Risk Factor	Low PID Risk	High PID Risk
String voltage	< 600V	1,000V+
Module certification	IEC 62804 certified	No PID certification
Climate	Arid, low humidity	Hot-humid (coastal Tamil Nadu, West Africa)
Grounding	System grounded	Floating or negative-grounded
Module technology	n-type silicon	p-type silicon (higher susceptibility)

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LeTID — The Hidden Risk in Hot-Climate PERC Deployments

LeTID deserves special attention for utility-scale projects in hot climates (India, MENA, West Africa) because it is less widely understood than LID and was not systematically incorporated in IEA simulations before 2019–2020.

LeTID Mechanism:

LeTID activates when p-type PERC modules operate at elevated temperatures (>50°C) under illumination. The mechanism is believed to involve hydrogen atoms migrating from the SiNx passivation layer into the silicon bulk under thermal activation, where they form metastable recombination centers. The defect density increases over weeks to months of hot-climate operation, then slowly anneals (recovers) over subsequent cooler periods.

The net effect is a degradation pattern that is:

• Not present at installation (unlike LID which appears immediately)
• Progressive over months 2–18 of operation
• Partially reversible during cooler winter periods
• Ultimately causing additional power loss on top of standard LID

LeTID Magnitude by Climate Zone:

Climate	Ambient Temperature Range	LeTID Risk	Estimated LeTID Loss
Rajasthan desert (India)	20–45°C	High	2–6% additional over first 2 years
Gulf Coast / MENA	25–50°C	Very High	3–8% additional
Karnataka / AP (India)	22–42°C	Moderate	1.5–4%
Germany / UK	5–30°C	Low	<1%
US Southwest (Arizona)	15–45°C	High	2–5%
West Africa (Sahel)	20–45°C	High	2–6%

LeTID in PVsyst Modeling:

Standard PVsyst LID configuration does not separately model LeTID. To incorporate LeTID into a bankable simulation for a hot-climate project:

1. Option A: Increase the LID input value to reflect total first-year power loss including both B-O LID and expected LeTID onset. For a PERC module in Rajasthan, this might mean entering 2.5–4.0% combined LID + early LeTID instead of the standard 1.5% LID-only value.

2. Option B: Increase the annual degradation rate for Years 1–2 in the PVsyst degradation schedule to reflect the progressive LeTID loss. This requires custom degradation table input (available in PVsyst 7+).

3. Option C: Apply a module-specific LeTID test result. Some manufacturers now provide LeTID characterization data from accelerated testing protocols. Use the measured LeTID loss from the test report as an explicit additional input.

For IREDA-funded projects, Option A is the most common practical approach; Option C is preferred when the procurement specification requires LeTID testing.

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25-Year Yield Modeling — PVsyst Configuration

For a bankable IEA, the simulation should model the full 25-year yield profile, not just Year 1. PVsyst’s multi-year simulation mode calculates energy yield for each year from Year 1 to Year N using the compounding degradation model.

PVsyst Multi-Year Simulation:

Navigate to: Advanced Simulation → Multi-Year Degradation

Configure:

• Start year: Year 1 (post-LID stabilization)
• End year: Year 25 (or 30 for newer projects with extended warranty periods)
• Annual degradation rate: 0.40–0.50% for PERC; 0.30–0.40% for TOPCon
• LID: Applied in Year 1 separately

The output is a table of annual energy (MWh) by year, which feeds directly into the financial model’s annual production schedule.

25-Year P50 Yield Impact — Comparison Example:

For a 10 MW project in Karnataka with 1,700 MWh/MWp Year 1 P50 yield:

Module Technology	Year 1 P50 (MWh)	Year 10 P50 (MWh)	Year 25 P50 (MWh)	25-yr Total P50 (MWh)
PERC (0.50%/yr, 1.5% LID)	16,745	15,980	14,825	385,400
TOPCon (0.35%/yr, 0.2% LID)	16,966	16,383	15,491	399,700
HJT (0.25%/yr, 0.1% LID)	16,983	16,560	15,887	410,100
Difference PERC vs HJT	—	−580	−1,062	−24,700
Revenue difference at ₹3.50/kWh	—	₹20.3 lakh/yr	₹37.2 lakh/yr	₹8.6 crore total

The ₹8.6 crore total revenue difference over 25 years between PERC and HJT on a 10 MW project — at the same ₹3.50/kWh PPA rate — represents a significant financing consideration. At a 8% discount rate, the NPV of this additional production is approximately ₹3.5–4.5 crore. For projects where HJT modules cost ₹1–2 crore more per 10 MW than PERC, the economics often favor HJT for long-duration PPA projects.

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Degradation and P90 — Uncertainty Modeling

The P90 exceedance probability is derived from the P50 estimate by applying uncertainty factors to quantify the range of possible outcomes. Degradation uncertainty is one of the major contributors to the P50-to-P90 gap.

Degradation Uncertainty Sources:

1. Manufacturing lot variation — modules from different production batches may have slightly different degradation rates even within the same model
2. LeTID inter-site variation — LeTID severity depends on actual operating temperature, which varies by site conditions and mounting configuration
3. Measurement uncertainty — the flash test that establishes nameplate at factory has ±2–3% uncertainty; degradation measurements in the field have similar uncertainty
4. Accelerated aging test limitations — laboratory degradation tests may not fully capture 25-year field degradation under specific climate conditions

Typical Degradation Uncertainty for P90 Calculation:

Degradation Uncertainty Factor	Value	P50-to-P90 Contribution
Annual degradation rate uncertainty	±0.1%/year	±2.5% over 25 years
LID uncertainty	±0.3%	±0.3% Year 1
LeTID uncertainty (hot climate)	±1.0–2.0%	±1.0–2.0% Years 1–3
Manufacturing Pmax uncertainty	±1.5%	±1.5% constant

For a bankable IEA, the total P50-to-P90 gap from degradation uncertainty alone is typically 2–4%. Combined with irradiance uncertainty, soiling uncertainty, and other factors, total P50-to-P90 gaps of 5–8% are common for utility-scale Indian projects.

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Module Warranty as Degradation Reference

Module manufacturer warranties specify two degradation guarantees:

1. Year 1 guarantee — typically ≥ 97–98% of nameplate power after 1 year (implicitly allowing for LID)
2. Linear annual degradation — typically ≤ 0.4–0.5%/year for PERC; ≤ 0.40%/year for TOPCon

The warranty guarantee is not the same as the expected degradation. Warranties are the minimum guaranteed performance — actual degradation for high-quality Tier-1 modules is typically better than the warranty floor.

Degradation Assumptions for IEA Documentation:

Approach	Description	Acceptability for IEA
Manufacturer warranty floor	Use exactly the linear warranty rate	Conservative; generally accepted
Manufacturer published typical	Use the typical (not minimum) degradation value	Accepted with manufacturer data sheet reference
Published field data	Use measured degradation from long-term operating plant studies	Preferred; requires peer-reviewed citation
Optimistic assumption (below warranty)	Use < 0.3%/year without supporting data	Not accepted without specific module test data

The NREL PV Degradation Database compiles field-measured degradation rates from thousands of PV systems worldwide. The median degradation rate across all technologies is approximately 0.5%/year (NREL, 2024), with modern monocrystalline PERC averaging 0.4–0.5%/year and n-type technologies showing 0.3–0.4%/year. The IEA PVPS Task 13 performance reports document degradation rates by technology, climate, and operating condition — these are accepted by independent engineers as primary references for IEA degradation assumptions. The IREDA financing documentation guidelines require that degradation assumptions in yield reports reference manufacturer warranty or published field performance data.

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Combining LID, LeTID, and Annual Degradation in a Complete Simulation

A comprehensive PVsyst degradation model for a hot-climate Indian utility-scale project includes:

1. LID — Enter 1.5–2.0% for PERC (or use manufacturer LID test report value); 0.0–0.2% for TOPCon/HJT

2. LeTID adjustment — For Rajasthan/Gujarat/MENA sites, add 1.0–2.0% to the effective Year 1 power loss (combined LID + LeTID onset) or use a stepped degradation rate for Years 1–3

3. Annual degradation — PERC: 0.45%/year; TOPCon: 0.35%/year; HJT: 0.25%/year (use manufacturer data if available)

4. PID — 0% for IEC 62804-certified modules in grounded systems; 0.5–1.5% for ungrounded high-voltage configurations without certification

5. P90 uncertainty — Apply ±0.1%/year degradation rate uncertainty; ±1.5% manufacturing Pmax uncertainty as contributors to P50-to-P90 uncertainty calculation

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How Heaven Designs Documents Degradation for IREDA and IFC

Heaven Designs includes a dedicated degradation section in every utility-scale PVsyst IEA report, with explicit documentation of:

• LID value and source (manufacturer test report or published benchmark)

• LeTID risk assessment and adjustment for hot-climate sites

• Annual degradation rate and source (NREL database, IEA PVPS data, or manufacturer warranty)

• PID risk assessment and loss assumption

• 25-year annual production table

• P50-to-P90 degradation uncertainty contribution

• Solar Ground Mount Design — Utility-scale PVsyst simulation with 25-year degradation modeling, LID/LeTID assessment, P50/P90 outputs.

• Solar Rooftop Detailed Engineering Design — Commercial and industrial PVsyst with technology-specific degradation modeling.

• MW-Scale PMC — Owner’s engineer oversight of module procurement with degradation warranty compliance.

• Site Survey and Land Feasibility — Module technology selection consulting based on site climate and degradation implications.

Related posts: PVsyst Loss Diagram Interpretation | PVsyst Soiling Loss Modeling India and Africa | PVsyst vs Helioscope for Utility-Scale | PVsyst Bifacial Gain Modeling Tutorial

Glossary: PVsyst, LID, PID, Performance Ratio.

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FAQ

What is the difference between LID and degradation in PVsyst?

LID (Light-Induced Degradation) is a one-time power loss that occurs in the first hours to days of exposure to sunlight, caused by boron-oxygen defect formation in p-type silicon. In PVsyst, LID is configured as a Year 1 loss (typically 1.0–2.0% for PERC modules) applied at the start of the simulation. Annual degradation is the ongoing, progressive power loss that continues from Year 1 through Year 25, configured as an annual percentage rate (typically 0.4–0.5%/year for PERC). LID is a one-time event; annual degradation is cumulative. Both are applied in PVsyst, and both should be documented with sources in a bankable IEA.

Should I enter 0.5% or 0.4%/year degradation for PERC modules?

For a bankable IEA, the degradation rate should reference the module manufacturer’s linear warranty guarantee or published field data. Most Tier-1 PERC manufacturers warranty ≤ 0.45%/year or ≤ 0.50%/year linear degradation. The NREL PV Degradation Database shows modern monocrystalline modules averaging approximately 0.4–0.5%/year. Using 0.45%/year as a balanced, industry-supported value is defensible; using 0.3%/year for PERC without specific manufacturer data or field evidence will be flagged by independent engineers as too optimistic.

What is LeTID and should it be modeled in PVsyst for Indian projects?

LeTID (Light and Elevated Temperature Induced Degradation) is a degradation mechanism in p-type PERC modules that activates at high operating temperatures (>50°C) combined with illumination — conditions that are routinely present in Indian ground-mount operation (Rajasthan, Gujarat, AP, Karnataka in summer). LeTID can cause 2–6% additional power loss in hot-climate sites, manifesting over months 2–18 of operation. Standard PVsyst LID configuration does not automatically model LeTID. For bankable IEA documentation of hot-climate PERC projects, LeTID risk should be addressed by increasing the LID input to include expected LeTID onset, or by using a stepped degradation rate for Years 1–3. N-type TOPCon and HJT modules are not susceptible to LeTID.

How does PID affect PVsyst simulation and what loss should I enter?

PID (Potential-Induced Degradation) is configured in PVsyst as an additional annual loss percentage under Module Array Losses. For modules with IEC 62804 PID certification and grounded string configurations, enter 0% PID loss and document the certification reference. For ungrounded configurations or modules without PID certification in hot-humid climates (coastal India, West Africa), a 0.5–2.0% annual PID loss is appropriate depending on string voltage and climate conditions. PID is reversible (by grounding or polarity reversal at night), so the bankable IEA should note whether PID mitigation is included in the O&M protocol.

How do I document degradation assumptions for IREDA loan documentation?

IREDA project appraisal for utility-scale loans requires the yield report to explicitly state the degradation assumption and its source. The standard documentation format: (1) state the annual degradation rate used (e.g., 0.45%/year); (2) cite the manufacturer warranty document specifying this as the maximum guaranteed annual degradation; (3) optionally cite NREL PV Degradation Database or IEA PVPS Task 13 data showing this rate is consistent with published field performance; (4) include the 25-year annual production table showing year-by-year yield from the PVsyst simulation. If LeTID risk is present, add a note on how it is addressed in the simulation inputs.

Which module technology should I select for minimum degradation in a 25-year Indian utility-scale project?

For minimum long-term degradation, HJT (heterojunction) modules have the lowest observed annual degradation (0.20–0.30%/year) and zero LID/LeTID risk. TOPCon is the practical next choice (0.30–0.40%/year; no LID/LeTID) and is more cost-competitive than HJT for utility-scale procurement in 2025–2026. Standard p-type PERC has higher degradation (0.40–0.50%/year) and LID/LeTID risk in hot climates. For a 25-year PPA where long-term production determines the investor IRR, TOPCon or HJT consistently outperform PERC on lifetime energy delivered — the technology premium is typically recovered within 3–5 years through higher annual yield.