PVsyst Energy Yield Simulation Guide for Solar EPC Engineers

PVsyst is the industry-standard software for solar energy yield simulation and is a mandatory deliverable for virtually every bankable solar project worldwide. Lenders, technical advisors, and EPCs all rely on PVsyst P50 and P90 output figures for financial modelling and performance guarantees. Yet many engineers use PVsyst without fully understanding which parameter choices have the greatest impact on accuracy — and which common shortcuts introduce systematic errors.

This guide walks through a PVsyst simulation workflow from project creation to final report, with specific guidance on parameter selection for projects using LONGi, Jinko, and JA Solar modules with Sungrow and Huawei inverters.

Step 1: Project Setup and Meteo Data Selection

PVsyst uses hourly Typical Meteorological Year (TMY) data as its primary irradiance input. The quality of the meteo data is the single biggest driver of P50 accuracy. For bankable projects, use at least one of:

• Meteonorm 8.x: Synthetic TMY derived from satellite and ground station data. Covers all global locations. Standard for European and Asian projects. Uncertainty ±4–5% annual GHI.
• Solargis: Satellite-derived database with 1–2% annual uncertainty for most locations. Preferred by IFC, ADB, and most project finance lenders. Available as PVsyst import (*.MET format).
• NASA POWER: Free, global, satellite-derived TMY. Higher uncertainty (±5–8%) but useful for feasibility and remote sites without Solargis coverage.
• On-site pyranometer data: Required by lenders for projects > 5 MW when data quality is paramount. Minimum 1–2 years of calibrated Class A pyranometer readings correlated against satellite data.

In PVsyst 7.x+, import the TMY file under Site Meteo → Import ASCII File. Always verify that the imported annual GHI matches your expected value from the data provider's summary sheet — import errors do occur.

Step 2: Array Configuration — Tilt, Orientation, and Pitch

PVsyst's orientation window calculates optimal tilt and azimuth for fixed-tilt systems. For single-axis trackers (SAT), use the "Tracking" mode with the appropriate axis orientation (typically North-South).

Key parameters to configure carefully:

• Ground Coverage Ratio (GCR): Pitch / Module height. Enter the physical pitch from the mounting design. PVsyst calculates inter-row shading losses from this value — errors here directly affect shading loss calculations.
• Height above ground: Critical for bifacial rear-side irradiance calculation. Enter the actual module centre height above ground surface (not pile height). For ground-mount on 2.3 m piles with 2.1 m modules at 15° tilt, the effective height is approximately 1.8 m.
• Albedo: Ground reflectivity coefficient. Default 0.20 (dry grass) is often used, but for desert sites use 0.25–0.35 (dry sand/rock) and for rooftop bitumen use 0.10–0.15. Albedo has significant impact on bifacial rear gain.

Step 3: System Definition — Strings, Inverters, and Modules

PVsyst's electrical design window defines the DC/AC architecture. Import the correct PAN file (module) and OND file (inverter) for your specified equipment:

When defining string length, PVsyst checks that Voc (at minimum expected temperature) does not exceed the inverter's maximum DC input voltage. For 1500 V DC systems, typical string length is 28–32 modules for 580–615 Wp panels. Always verify the string sizing against the inverter spec sheet's Vmax input and Vmpp range.

Step 4: Loss Parameters — The Heart of Accuracy

PVsyst's loss tree defines every energy reduction factor between module STC output and AC meter output. The most impactful parameters:

• Thermal loss coefficient (Uc, Uv): Default Uc = 29 W/m²K (free-standing). For rooftop close-mounted systems, use Uc = 15–20 W/m²K (restricted airflow). Wrong Uc choice shifts temperature loss by 2–4%.
• Module quality (LID, tolerance): Enter the actual flash-test power deviation from the ordered modules once available. For design stage, use 0% (assuming positive-tolerance modules at STC rating).
• Soiling loss: Enter monthly soiling profile. For desert projects, use 2–3%/month with zero cleaning (to model worst case) or apply a cleaning schedule reducing monthly loss to 0.5–1.5% mid-month.
• Wiring loss: Enter the actual Ohmic loss percentage from your cable sizing calculation. Typically 0.5–1.5% for well-designed systems.
• Unavailability: Enter planned and unplanned system downtime. For utility-scale with remote monitoring and < 4-hour response SLA, use 0.5–1.0% annual unavailability.

For bifacial modules, enable "Bifacial" in the module definition. PVsyst's bifacial model calculates rear-side irradiance from the defined albedo and module height. Typical bifacial gain contribution in PVsyst ranges 2–8% depending on albedo and height — consistent with real-world measurements from LONGi and Jinko bifacial field studies.

Step 5: Shading — Near Shading and Electrical Effect

PVsyst offers three near-shading calculation methods:

• Module Layout (most accurate): Define each module's position on the table, enabling PVsyst to calculate electrical mismatch losses from partial row shading. Required for bankable reports.
• According to strings: Intermediate accuracy. Suitable for systems with string-level MLPE where partial shading impacts are isolated.
• Linear (fastest): Assumes shading loss reduces output linearly. Underestimates electrical mismatch losses by 1–3% in shading-affected systems.

Import 3D horizon profiles under the Shading scene. For utility-scale projects, upload a LiDAR-derived horizon profile from the site survey. For rooftop projects, manually place surrounding objects (parapets, HVAC units, neighbouring buildings) in PVsyst's 3D environment.

Step 6: P50 vs P90 — Uncertainty and Bankability

A single PVsyst simulation produces a P50 estimate — the expected annual energy output. For project finance, lenders require a P90 figure representing the 90th percentile (exceeded in 9 out of 10 years). P90 is calculated by applying uncertainty factors to the P50:

P90 = P50 × (1 − 1.28 × σ_combined)

Where σ_combined is the combined relative standard deviation of all uncertainty sources:

PVsyst's Monte Carlo uncertainty module automates this calculation. Input the σ values for each category, and PVsyst produces the P90 directly. Independent engineers typically verify these uncertainty inputs for lender technical due diligence.

Common PVsyst Mistakes to Avoid

• Using the default soiling loss of 0% — always enter a site-appropriate monthly profile.
• Using Meteonorm synthetic data for sites within 30 km of a ground station — always import the nearest real-station data.
• Forgetting to enable the bifacial model for bifacial modules — LONGi Hi-MO 7 bifacial yield gain of 4–7% is lost if the standard (monofacial) model is used.
• Not validating PAN file against manufacturer flash-test reports — PVsyst's online database sometimes contains outdated or incorrect parameters.
• Setting thermal Uc = 29 for all systems — closed rooftop installations run 5–10°C hotter per cell temperature, increasing temperature losses by 1.5–3%.

Equipment Datasheets and PAN Files from Econo Solar

Econo Solar provides customers with PAN files, OND files, and flash-test data for all modules and inverters we supply. Our technical team verifies that PAN file parameters match the shipped batch's flash-test statistics. This saves project developers weeks of back-and-forth with manufacturers and ensures your PVsyst simulation accurately represents the equipment on site.

To request PAN/OND files alongside a factory quote for your project, submit your enquiry here.