A PVsyst loss diagram is one page that decides whether your project gets financed. Lenders send it to their Independent Engineer on day one. The IE marks it up. The bank’s credit committee reads the marked-up version and decides how much debt to extend. If the loss diagram shows inputs that a lender has seen rejected before — an irradiance dataset with high uncertainty, a near-shading loss above 5%, an availability number that does not match your O&M contract — the financing slows or stalls entirely.
Direct answer. The PVsyst loss diagram is a waterfall energy budget that starts with gross irradiance hitting the array and subtracts every physical, electrical, and operational loss to produce net AC energy delivered to the grid. The 7-Layer Loss Stack — irradiance losses, optical losses, thermal losses, wiring losses, mismatch losses, availability losses, and grid curtailment — is the structured framework for reading and auditing this chart. Independent Engineers flag any single layer above published benchmarks as a bankability risk, and a clean loss diagram compresses project financing timelines by 3–6 weeks.
This walkthrough is written for project managers, developers, and EPC founders who need to read a PVsyst report with the same eye a lender’s IE uses. Whether you are working on a 2 MW rooftop in Maharashtra or a 50 MW ground-mount bidding into a SECI auction, the loss diagram logic is the same. The numbers differ by site; the structure does not. For context on common simulation errors that corrupt the diagram, the PVsyst error guide is the companion reference.
What the PVsyst Loss Diagram Actually Shows
The loss diagram is a visual energy budget. It starts at the top with the total irradiance incident on the plane of array and walks downward through every mechanism that converts that energy into something smaller than the nameplate rating suggests.
The diagram is not a single number. It is a sequence of percentage deductions, each corresponding to a specific physical phenomenon. When a lender or IE reviews the report, they are checking whether each deduction is:
- Physically plausible for the site conditions.
- Consistent with the input assumptions fed into PVsyst.
- Within the range published by IRENA’s global PV benchmarking studies for that project type.
The diagram also tells the IE whether the simulation was run with realistic or optimistic inputs. A shading loss of 0.5% on a dense urban rooftop signals that the near-shading scene was either not modeled or modeled incorrectly. An IE flags that immediately.
Definition. The PVsyst loss diagram is a waterfall energy budget — a standard output of PVsyst simulation software — that quantifies every loss mechanism between incident irradiance and net AC energy delivered to the grid. It is the primary document used by Independent Engineers to validate energy yield assumptions during project financing due diligence.
The diagram appears in the PVsyst simulation report under the heading “Loss Diagram” or “Energy Balance.” In a bankable report, this page is the one page your lender’s IE reads most carefully. The ratio of net AC output to theoretical maximum output is the Performance Ratio — the summary metric that falls out of all these losses combined.
The 7-Layer Loss Stack — Your Framework for Reading the Diagram
The named framework for this walkthrough is The 7-Layer Loss Stack. It maps every entry on the PVsyst loss diagram to one of seven layers, in the physical order they occur. Reading losses in this sequence — rather than jumping between entries — prevents the common mistake of misattributing a loss to the wrong cause, which leads to incorrect design responses.
Irradiance Losses
Horizon shading, near shading from structures and neighboring buildings, and soiling. These are the first losses applied to gross GHI converted to POA irradiance. Horizon shading is site-fixed. Near shading depends entirely on the accuracy of the 3D scene model built in PVsyst.
Optical Losses
Incidence angle modifier (IAM) losses — also called reflection losses — that increase as sunlight hits the module at shallower angles during morning and evening. Fixed-tilt arrays have higher IAM losses than single-axis trackers, because trackers reduce the oblique-angle hours.
Thermal Losses
Module operating temperature derates output via the temperature coefficient. PVsyst calculates NOCT-based cell temperature from ambient temperature, wind speed, and irradiance. In Rajasthan or Tamil Nadu, thermal losses of 6–9% are normal across the year.
Wiring Losses
Ohmic losses in DC strings, combiner boxes, and AC cables. PVsyst models these from conductor sizing inputs. A well-designed system targets DC wiring losses below 1.5% and AC losses below 0.5%. Values above these thresholds indicate cable undersizing that can be corrected in design.
Mismatch Losses
Power loss from module-to-module variation in Vmp and Imp within a string. PVsyst uses a fixed mismatch loss factor, typically 0.5–2.0%. Values above 2.5% for a new project signal either high power-tolerance bins or partial shading being double-counted against the shading layer.
Availability Losses
Planned and unplanned downtime — inverter trips, maintenance windows, grid faults. Standard lender expectation: 1.0–2.0% for a well-operated plant with a competent O&M contractor. Values below 0.5% are challenged by IEs unless backed by a contractual uptime SLA with liquidated damages.
Grid Curtailment
Energy produced but not absorbed by the grid due to transmission congestion or DISCOM-mandated curtailment. In India, this requires a separate curtailment risk disclosure aligned with the project's Power Purchase Agreement. In the USA, curtailment risk is flagged in CAISO and ERCOT interconnection studies.
Apply the 7-Layer Loss Stack by reading the PVsyst loss diagram from top to bottom. Record each layer’s percentage. Compare each number to the benchmarks in the sections that follow.
Layer 1 — Irradiance Losses: The Foundation of Every Number
Irradiance losses set the ceiling for everything else. If the irradiance inputs are wrong, every downstream number is wrong. This is why lenders require the simulation to use a named, calibrated meteorological dataset — either Meteonorm 8.x, Solargis TMY, or NSRDB TMY3 for US projects.
0–3%
Horizon shading loss (typical range)
IRENA PV cost benchmarks, 2022
1–4%
Near shading loss (rooftop systems)
PVsyst documentation, 2024
2–5%
Soiling loss (India, dry season avg.)
NREL PV soiling assessment, 2023
±3–8%
Meteo dataset uncertainty (P90 vs P50)
Solargis Uncertainty Assessment, 2024
The near-shading scene deserves special attention. PVsyst models near shading in two modes: linear (simple linear shading factor) and “according to module strings” (string-by-string bypass diode modeling). Lenders and IEs expect the string mode for any project where shading occurs. A report that uses linear shading on a densely obstructed rooftop is a red flag that will trigger an IE comment.
Soiling loss is the most site-specific irradiance input. In Gujarat, Rajasthan, and Tamil Nadu, a 3% annual soiling loss is defensible with a twice-monthly cleaning schedule. In regions near industrial areas or highways, 5–6% may be correct. A soiling assumption with no supporting cleaning schedule document will be challenged.
Field tip. Always attach the O&M cleaning frequency agreement to the PVsyst report when submitting to a lender. The soiling loss percentage in the loss diagram must match what the O&M contract states — otherwise the IE flags a discrepancy on the first review pass, adding 2–3 weeks to the cycle.
Layers 2 and 3 — Optical and Thermal Losses: The Physics You Cannot Negotiate
Optical and thermal losses are largely determined by physics and equipment selection. They are harder to improve through design choices than irradiance losses, but understanding them helps you catch simulation errors before the lender does.
Optical losses (IAM) typically range from 2.5% to 4.5% for fixed-tilt systems and 1.5% to 3.5% for single-axis trackers. A value below 1.5% on a fixed-tilt system at a high-latitude site is physically implausible and signals that the IAM model was not applied correctly. PVsyst uses the ASHRAE model by default; for bifacial modules, the bifacial model must be activated separately or the rear-gain calculation will be incomplete.
Thermal losses are calculated from ambient temperature, wind speed, and the module’s NOCT or TONC value. For monocrystalline PERC modules with a temperature coefficient of -0.35%/°C, every 1°C above STC costs 0.35% output. At a site where the average operating temperature is 45°C (20°C above STC’s 25°C), the thermal loss is 7%. At 55°C operating temperature — common in Rajasthan summer afternoons — the instantaneous loss reaches 10.5%.
| System Type | IAM Loss (typical) | Annual Thermal Loss (India) | Annual Thermal Loss (USA Southwest) |
|---|---|---|---|
| Fixed-tilt ground mount | 3.0–4.0% | 5–8% | 4–7% |
| Single-axis tracker | 2.0–3.0% | 4–7% | 3.5–6% |
| Rooftop (flush-mounted) | 3.5–4.5% | 6–10% | 5–8% |
| Carport canopy | 3.0–4.0% | 5–8% | 4–7% |
| Floating solar | 2.5–3.5% | 3–5% | 2–4% |
Floating solar typically shows the lowest thermal losses because the water surface reduces ambient temperature near the array. According to NREL’s floating PV technical report (2021), floating arrays can show 5–12% higher annual generation compared to ground-mount equivalents in hot climates, primarily through reduced thermal losses. The PVsyst floating solar setup guide covers how to configure PVsyst to capture this correctly.
Layers 4 and 5 — Wiring and Mismatch Losses: The Design-Controlled Numbers
Wiring and mismatch losses are the layers a good electrical design directly controls. If you see high values here, the issue is design-correctable before the project gets built.
DC wiring losses result from resistance in the string cables between modules and the inverter or combiner box. The loss percentage equals (cable resistance × string current squared) divided by module DC power. Target: below 1.5% for DC wiring. An experienced designer achieves 0.8–1.2% through careful cable cross-section selection — typically 4 mm² or 6 mm² for residential and commercial strings, and 10 mm² or 16 mm² for utility-scale with long string runs.
AC wiring losses apply to the cable between the inverter output and the grid connection point. Target: below 0.5%. Higher values indicate undersized AC cables or unexpectedly long runs to the metering point.
Watch out. A DC wiring loss above 2.5% in a PVsyst report almost always means the simulation was run with default cable lengths that do not match the actual site layout. IEs routinely reject reports where the wiring loss cannot be reconciled with actual cable run lengths in the single-line diagram. This discrepancy can add 2–3 weeks to the IE review cycle.
Mismatch losses quantify the power penalty from cell-to-cell and module-to-module variation. PVsyst implements mismatch as a fixed percentage loss applied to DC output. The correct value depends on module power tolerance class. For modules with a ±3% tolerance (common in tier-2 procurement), 1.0–1.5% mismatch is appropriate. For ±2% tolerance modules — most Tier-1 ALMM-listed modules — 0.5–1.0% is defensible.
The single-line diagram is the document that anchors both the wiring loss calculation and the IE’s cable schedule reconciliation. Without a complete SLD that matches the PVsyst system configuration, the IE cannot confirm the wiring loss figure.
Layers 6 and 7 — Availability and Curtailment: Where the P&L Lives
Availability and curtailment losses are the layers most directly connected to project revenue and O&M contract terms. They are also the layers IEs scrutinize most intensely.
Availability in PVsyst is a user-entered fixed percentage representing expected system downtime: inverter trips, maintenance windows, grid utility outages, and communication failures. Standard lender benchmarks:
| Availability Loss | IE Interpretation |
|---|---|
| 0.0–0.5% | Challenged — typically too optimistic unless backed by a contractual uptime guarantee |
| 0.5–1.0% | Acceptable for new systems with comprehensive O&M contracts |
| 1.0–2.0% | Standard — most mature utility-scale projects fall here |
| 2.0–3.0% | Flag for review — requires O&M contract justification |
| Above 3.0% | Red flag — implies chronic grid reliability issue or poor O&M performance |
Grid curtailment is not always modeled in PVsyst. When it is modeled, it appears as a separate loss line at the bottom of the diagram. In India, projects in states with chronic curtailment — Andhra Pradesh, Tamil Nadu during low-demand monsoon months — should model 3–8% curtailment risk and include a curtailment risk appendix in the project information memorandum. According to IEA’s Solar PV supply chain analysis, curtailment risk is growing globally as variable renewable penetration increases past 15% of grid capacity.
How Lenders and IEs Read the Loss Diagram
A lender’s Independent Engineer does not read the loss diagram top to bottom the way this article presents it. They use a prioritized review sequence designed to identify the highest-risk entries in the shortest time.
IE review sequence:
- Irradiance dataset — what source, what year range, what uncertainty value? A Meteonorm dataset from a station more than 30 km from the site without site-measured validation triggers an immediate comment.
- Near-shading loss — is the 3D scene attached as a supporting document? Was string-level shading applied or linear?
- Soiling loss — does the value match the O&M cleaning schedule and regional soiling rate data?
- Availability loss — does it match O&M contract SLA terms?
- Overall performance ratio (PR) — the IE compares PR to published benchmarks. According to NREL’s photovoltaics research program, a well-designed utility-scale monocrystalline system in a high-irradiance climate achieves PR of 78–83%. A simulated PR above 85% triggers a “too optimistic” comment.
- Wiring losses — reconciled against SLD cable schedule.
- Mismatch — reconciled against module power tolerance class in the bill of quantities.
The IE documents all comments in a tracking log. Each comment delays final IE sign-off by the time required to respond and revise. A clean loss diagram — one that passes the IE’s review sequence without comments — can compress the financing timeline by 3–6 weeks on a ₹50 crore or larger project.
Want to see what a bankable PVsyst report looks like?
Download a redacted sample PVsyst report — complete loss diagram, meteo validation, uncertainty analysis, and IE-ready format. Used on a 10 MW SECI-bid project in Rajasthan.
Get the sample pack →What a High-Performing Loss Diagram Looks Like
A loss diagram that sails through IE review has a consistent profile. Use this as your benchmark when reviewing your engineer’s PVsyst output before sending it to a lender.
| Loss Layer | Acceptable Range | Typical “IE Pass” Value | Watch Level |
|---|---|---|---|
| Horizon shading | 0–3% | 0.5–1.5% | Above 4% |
| Near shading | 0–6% | 1–3% | Above 6% |
| Soiling | 1–6% | 2–4% | Above 7% |
| IAM (optical) | 1.5–4.5% | 2.5–3.5% | Below 1% or above 5% |
| Thermal (India) | 3–10% | 5–8% | Above 12% |
| DC wiring | 0.5–2.0% | 0.8–1.5% | Above 2.5% |
| Mismatch | 0.3–2.0% | 0.5–1.0% | Above 2.5% |
| Availability | 0.5–2.0% | 1.0–1.5% | Below 0.3% or above 3% |
| LID + degradation | 0.5–2.5% | 1.0–2.0% | Above 3% |
Reading the loss diagram against these benchmarks takes less than five minutes once you know the 7-Layer Loss Stack structure. Flag any entry outside the “Watch Level” column before submitting to a lender.
How to Improve a Loss Diagram Before Lender Submission
If your current PVsyst report shows values that will draw IE comments, you have two paths: correct the simulation inputs if they are genuinely wrong, or document the site conditions that justify the number.
Irradiance layer improvements:
- Replace Meteonorm with Solargis site-measured or satellite-derived TMY if the station is more than 20 km from the site.
- Add the uncertainty analysis page showing P50 and P90 values. Lenders for projects above ₹50 crore financing typically expect explicit uncertainty quantification.
- Attach the 3D near-shading scene as a PDF or screenshot with the module rows labeled.
Wiring layer improvements:
- Run the simulation with actual cable lengths from the SLD rather than default PVsyst lengths.
- Increase cable cross-section if DC wiring loss exceeds 1.5%.
- Document the AC cable route length from inverter to grid connection point.
Availability layer improvements:
- Attach the O&M contract SLA that specifies the contractual uptime guarantee.
- If availability is modeled at 1.0% or better, confirm the O&M contractor has a documented track record of achieving those uptime levels at comparable sites.
According to PVsyst’s official user documentation, the availability loss parameter is a user-defined input with no automatic validation — the simulation accepts any value entered without checking it against physical reality. It is entirely the engineer’s responsibility to input a defensible number backed by site-specific evidence.
Note. PVsyst 7.4 introduced a formal uncertainty analysis module that generates a P50/P90/P99 energy distribution. This is now the expected format for lender-grade reports in most Indian and international financing transactions. If your report was generated in PVsyst 6.x, the IE may request an updated simulation in the current version.
For the complete document package lenders expect alongside the simulation file, the bankable PVsyst reports guide walks through the meteo uncertainty report, 3D scene file, and system parameter validation documents that must accompany the loss diagram submission.
How Heaven Designs Helps
Heaven Designs prepares PVsyst simulation reports that pass IE review on the first submission. The process starts with site-validated meteo data, includes a calibrated 3D near-shading scene, and produces a loss diagram where every entry is documented with a source reference or contract backing. Every report includes a one-page Loss Diagram Audit Sheet that maps each loss layer to its source assumption and benchmark reference — the same format IEs use internally.
- Solar Rooftop Detailed Engineering Design — Full IFC-grade package: PVsyst simulation, loss diagram with source documentation, SLD, GA, structural bill of quantities, and mounting specification. Delivered in 5–7 business days.
- Solar 3D Pre-Design — Sales-stage 3D shading model and yield estimate in 48 hours. The 3D scene feeds directly into the bankable PVsyst simulation when the project advances to detailed design.
- Electrical CEIG Drawings — CEIG-approval-ready electrical drawings that align with the SLD inputs used in the PVsyst simulation — no reconciliation gap for the IE to flag.
- Download a sample deliverable — See a redacted PVsyst report including the loss diagram, meteo report, and 3D scene documentation.
Contact us to discuss your project’s bankability requirements. Heaven Designs has delivered PVsyst simulation packages accepted by IREDA, PFC, SBI Capital, and international DFI-appointed IEs on projects from 500 kW to 100 MW.
FAQ
What is the difference between a loss diagram and a performance ratio in PVsyst?
The loss diagram shows individual percentage losses for each physical mechanism, stacked from gross irradiance to net AC output. The performance ratio (PR) is the single number that results from all losses combined — it represents actual AC output divided by what an ideal system at STC would produce for the same irradiance. A typical utility-scale PR is 78–84%. The loss diagram explains why the PR is what it is; the PR alone does not tell you which losses drove it.
What irradiance dataset does a lender prefer for an Indian project?
Most Indian lenders financing projects above ₹25 crore expect either Meteonorm 8.x with a weather station within 25 km of the site, or Solargis satellite-derived TMY data. IMD (India Meteorological Department) data is acceptable for preliminary reports but typically not for final due diligence submissions. The dataset choice must match what the project’s energy yield assessment (EYA) report documents.
Why does PVsyst show different results when I change from linear to string-level shading?
Linear shading applies a uniform loss factor across the entire array at each timestep. String-level shading models bypass diode activation in each affected string separately. String-level shading almost always produces a lower simulated energy yield because it correctly captures the non-linear impact of partial shading on string output. If your linear shading simulation shows 1% near-shading loss but string-level shows 3.5%, the 3.5% number is more accurate. Lenders require string-level shading for any project with significant near-shading obstructions.
What availability loss percentage does a lender typically accept without challenge?
The standard range accepted without challenge is 1.0–2.0%. Values below 0.5% are questioned unless the O&M contract includes a contractual uptime guarantee above 99% backed by liquidated damages. Values above 2.5% are questioned because they imply poor O&M quality and lower revenues, which directly reduces debt service coverage ratios. Contact us if you need help calibrating this figure to your O&M terms.
How do I model grid curtailment in PVsyst?
PVsyst does not model curtailment directly as a loss layer in the standard loss diagram. Curtailment is modeled through the “Grid power limitation” input in the system configuration, which caps AC output at the contracted injection capacity. For projects where curtailment is a material risk, engineers also apply a separate curtailment loss factor in the “System losses” section, documented with grid operator curtailment data for the relevant state or region.
What is an acceptable total PR for a utility-scale project in India?
For a monocrystalline PERC or TOPCon fixed-tilt ground-mount system in a high-irradiance Indian location (GHI above 5.5 kWh/m²/day), a simulated PR of 78–82% is standard and lender-accepted. For single-axis tracker systems, 80–84% is typical. A simulated PR above 85% will draw an IE comment requesting justification of the optimistic loss assumptions.
Does the loss diagram change between PVsyst and Helioscope simulations?
PVsyst and Helioscope use different loss modeling structures. PVsyst’s loss diagram is the universally accepted format for lender due diligence and IE review in India and most international markets. Helioscope produces a loss table but does not generate the identical waterfall format, and its uncertainty analysis module is less developed. For any project requiring a bankable energy yield assessment, PVsyst simulation is required. Helioscope is appropriate for bid-stage yield estimates and layout optimization.
How long does an IE review of the PVsyst loss diagram typically take?
A clean loss diagram with all supporting documentation — 3D shading scene, meteo report, uncertainty analysis, cleaning schedule — typically clears IE review in 2–3 weeks as part of broader due diligence. A loss diagram with IE comments requiring engineer response adds 2–6 weeks depending on the number of comment rounds. Heaven Designs’ experience across the EPC project workflow shows that pre-submission audit of the loss diagram reduces IE comment rounds by approximately 60%, compressing the overall financing timeline meaningfully.
