PVsyst vs SAM — Which Is Bankable for Solar Yield Studies

Two tools dominate bankable solar yield simulation in 2026: PVsyst, the Swiss commercial platform used by virtually every independent engineer, and SAM (System Advisor Model), NREL’s free, open-source simulation environment. Both produce credible energy estimates. Only one is universally accepted at the lender’s desk — and understanding why shapes how you budget your simulation workflow and where you invest time in model validation.

This guide examines the technical differences between PVsyst and SAM, explains why project finance has converged on PVsyst as the standard, and identifies the specific use cases where SAM adds genuine value. It also covers the dual-model approach that leading independent engineers increasingly recommend for large utility-scale projects.

Key Takeaway: PVsyst is the industry standard for bankable yield reports because independent engineers, lenders, and rating agencies have validated its methodology over two decades. SAM is a powerful research and cross-check tool. The optimal workflow uses SAM to challenge PVsyst assumptions, not to replace the primary simulation.

What PVsyst Is and What It Does

PVsyst is a Windows-based commercial simulation software developed at the University of Geneva and subsequently commercialised. Version 7 and later include significant updates to bifacial simulation, tracker backtracking models, and meteo data handling.

Its core function is deterministic hourly energy simulation — taking an irradiance dataset and running it through the full loss chain to produce net AC energy at the grid connection point.

Key PVsyst capabilities relevant to bankable yield:

• Detailed irradiance transposition (isotropic, Perez, Hay-Davies models)
• Shadings by horizon, near and far objects, and electrical mismatch from partial shading
• Temperature modelling with multiple cell temperature models (Faiman, Ross, and others)
• Bifacial gain simulation with the PVsyst bifacial model and adjustable albedo
• Single-axis and dual-axis tracker simulation with backtracking
• Detailed loss cascade including soiling, mismatch, wiring, transformer, and availability
• Meteo data import from Meteonorm, Solargis, NSRDB, and custom files

PVsyst outputs the standard deliverables that independent engineers use: loss diagram (Sankey chart), monthly production table, and simulation parameters summary. These outputs are what lenders expect to see in a yield report appendix. The simulation methodology is explicitly referenced in IEC 61724-3, the international standard for photovoltaic system performance monitoring.

PVsyst is priced at approximately $1,200–1,800 USD per year for a professional licence. It runs only on Windows. The simulation methodology is extensively peer-reviewed through academic literature and industry validation studies published by NREL, Sandia, and the University of Geneva itself.

For a detailed walkthrough of how to interpret PVsyst output files, our post on reading the PVsyst loss diagram covers each node in the Sankey chart and the thresholds that flag modelling issues.

What SAM Is and What It Does

SAM (System Advisor Model) is a free simulation tool developed and maintained by NREL (National Renewable Energy Laboratory) under US Department of Energy funding. It is available for Windows, Mac, and Linux.

SAM capabilities include:

• Photovoltaic simulation using the CEC (California Energy Commission) module database and SAM Detailed model
• Parabolic trough, power tower, and linear Fresnel CSP models
• Wind, biopower, and geothermal simulation
• Financial modelling including LCOE, NPV, payback period, and incentive structures
• Parametric analysis and Monte Carlo uncertainty analysis natively built in
• Scripting via LK language for automated batch runs across sites and configurations

SAM also imports NSRDB weather data directly and can use EPW files from EnergyPlus. Its module database is extensive and regularly updated from the CEC database.

The key difference from PVsyst: SAM was built to model the economics of entire technology portfolios for government policy analysis. Its physics models are solid and have been validated extensively, but the output format and workflow are not calibrated to lender expectations. An SAM output does not look like the PVsyst Sankey diagram and monthly table that independent engineers reach for when opening a yield report.

The Bankability Question: Why PVsyst Wins at the Lender’s Desk

Why has PVsyst achieved this dominance?

Longevity and peer review: PVsyst has been in active use since 1994. Its methodology has been validated against measured production data from thousands of plants across five continents. When an IE reviewer examines a PVsyst loss diagram, they apply pattern recognition built over years of reviewing the same format.

Standardised output: The PVsyst loss diagram (Sankey chart) and monthly production table are universally recognised. IEs review them in a standard template without customisation. An SAM report requires the IE to translate output formats, which adds time and introduces the risk of misinterpretation.

European and IEC alignment: European financial institutions adopted PVsyst as the standard early in the solar finance era, and that preference propagated to global project finance via European DFIs and banks. IFC, ING, Societe Generale, and Deutsche Bank all reference PVsyst methodology in their yield report requirements.

Module and inverter databases: PVsyst maintains the largest commercially curated module and inverter database, reducing the risk of equipment parameter errors from using manufacturer-provided specs in a custom model file.

SAM is not without its advocates in the finance world. Some US federal energy agencies (DOE programmes, USDA REAP grants) explicitly reference SAM in programme guidelines. A small number of US community solar lenders accept SAM reports when accompanied by a sensitivity analysis. But these remain edge cases in the broader project finance landscape.

The Bankability Acceptance Test: Five Criteria Lenders Apply

When an independent engineer reviews a yield report for a project finance transaction, they apply an implicit five-criterion test to determine whether the simulation methodology is acceptable. Understanding these criteria explains exactly why PVsyst passes and SAM-only reports typically do not.

Understanding this five-criterion test explains why our bankable PVsyst reports guide places such emphasis on documentation and traceability — not just the P50 number itself.

Feature-by-Feature Comparison

Where SAM Outperforms PVsyst

SAM has genuine advantages that make it valuable as a secondary tool and the primary tool in specific contexts.

Native Monte Carlo analysis: SAM allows you to define probability distributions for key input parameters (GHI uncertainty, temperature coefficient spread, soiling range) and run thousands of simulations automatically. The output is a full production probability distribution from which P50, P90, and P99 can be read directly. PVsyst requires manual uncertainty budget calculation using root-sum-of-squares — an algebraic approximation of what SAM computes numerically. For developers who want rigorous probabilistic analysis without manual uncertainty budget construction, SAM’s Monte Carlo is a genuine advantage.

Financial integration: SAM’s built-in financial models (PPA, third-party ownership, merchant market, LCOE) allow you to run energy and economics in one environment. PVsyst requires exporting energy data to a separate financial model spreadsheet. For rapid pre-feasibility analysis, this integration saves significant time.

Scripting and automation: SAM’s LK scripting language allows automated batch runs across multiple sites, weather files, or equipment configurations. PVsyst offers some scripting but is primarily GUI-driven. For portfolio analysis across 50+ sites, SAM’s automation capability is a substantial productivity advantage.

Open source transparency: For researchers and policy analysts, SAM’s open-source codebase allows full audit of calculation methods. PVsyst is proprietary, which creates friction for academic review. NREL publishes SAM validation studies with full methodology disclosure, as documented in the NREL SAM validation report.

Multi-technology: SAM handles wind, CSP, and storage alongside PV. For hybrid project analysis (PV + BESS, PV + wind, solar + hydro), SAM is the more capable environment. PVsyst is PV-only.

Cross-platform support: SAM runs on Mac and Linux. For teams with non-Windows development environments (increasingly common in data science and software-forward organisations), this is a practical advantage.

The Dual-Model Approach: When It Is Worth It

Leading independent engineering firms increasingly recommend a dual-model approach for large utility-scale projects. The workflow is straightforward:

1. Run the primary bankable simulation in PVsyst — this is the number submitted to the lender
2. Run a parallel simulation in SAM using the same weather file and comparable equipment parameters
3. Compare P50 results — if they agree within ±2 %, confidence in the PVsyst result increases significantly
4. If they diverge by more than 3 %, investigate the source of disagreement (typically shading, bifacial gain, or soiling modelling differences)
5. Document the comparison in the yield report as a cross-validation table

This approach adds cost (typically 15–25 % additional simulation time) but reduces the risk of IE rejection and provides a natural quality assurance gate. When a cross-validation table shows PVsyst and SAM agreeing within 1.5 %, an IE reviewer gains confidence that the PVsyst result is not an artefact of the tool’s modelling assumptions.

Heaven Designs offers dual-model simulation as a premium option within our PVsyst simulation service. For projects above 10 MW, we recommend the dual-model approach when the lender’s IE is one of the firms known to run their own SAM cross-check independently.

Simulation Tool Selection: The 3-Tier Decision Matrix

When a client asks which simulation tool to use, we apply a structured decision process that maps project type to tool selection.

Tier 1 — Project Finance / Lender Required Any project requiring external debt or equity from institutional sources. Output: PVsyst primary simulation, SAM cross-check if project exceeds 10 MW or lender specifies dual-model. Rationale: bankability is non-negotiable and PVsyst is the accepted standard.

Tier 2 — Internal Feasibility / Investment Decision Developer or EPC estimating project economics before committing to land or PPA. Output: SAM for rapid parametric analysis across sites and configurations, PVsyst for final selected configuration. Rationale: SAM’s speed and cost advantage outweighs bankability concerns at pre-commitment stage.

Tier 3 — Policy / Research / Grant Applications Academic institutions, NGOs, government agencies. Output: SAM primary (often specified by programme guidelines), PVsyst as supplementary if required. Rationale: SAM is explicitly referenced in DOE, USAID, and World Bank programme documentation for renewable energy analysis.

The International Renewable Energy Agency’s (IRENA) renewable cost analysis methodology explicitly distinguishes between tools used for policy modelling and tools required for project finance, which aligns with this three-tier approach.

Meteo Data Handling: A Critical Difference

Both tools accept TMY (typical meteorological year) data, but their native datasets and integration approaches differ significantly.

PVsyst integrates natively with Meteonorm and Solargis. It also imports NSRDB hourly data via a CSV import workflow. The Meteonorm integration is the most direct and is the default for European and Indian projects. Solargis integration requires a separate data purchase but provides the most accurate data for Indian and African projects.

SAM integrates natively with NSRDB via a direct API connection in the web-based NSRDB data viewer. SAM can also import EPW files from EnergyPlus, which covers global locations from the EnergyPlus weather database. The NSRDB integration is SAM’s strongest meteo advantage for US projects.

For Indian projects, PVsyst’s Solargis integration gives it a clear advantage — Solargis has the most comprehensive Indian irradiance dataset with the lowest stated uncertainty. For US projects, SAM’s NSRDB integration is a genuine strength that partially offsets PVsyst’s format advantages.

For projects in sub-Saharan Africa, Meteonorm coverage is variable and ground station density is low. Our solar consulting services for African EPCs include a meteo source evaluation step before simulation begins. The detailed methodology for selecting meteo sources across different geographies connects directly to the P90 calculation approach described in our guide to P50 and P90 in solar yield reports.

Comparison of Loss Modelling Depth

One dimension where the tools diverge most significantly is electrical loss modelling. This matters most for complex sites with shading objects, non-standard configurations, or bifacial modules.

For complex sites with significant shading (rooftop, terrain-influenced ground-mount, agrivoltaic), PVsyst’s 3D shading engine produces materially different results from SAM. For simple flat-ground utility-scale sites with no near shading, the tools converge more closely — typically within 1–3 % for the same weather file.

The shading engine difference is especially relevant for the increasingly common ground-mount tracker configurations, where row-to-row shading, backtracking algorithm fidelity, and GCR optimisation each affect final yield by 0.5–2 %. Our guide on the PVsyst loss diagram and Sankey chart interpretation shows exactly which nodes in the loss chain are most sensitive to tool selection.

Key Metrics Comparison

Pros and Cons Grid

Regulatory and Standard Alignment

One often-overlooked dimension in the PVsyst vs SAM debate is alignment with formal standards and regulatory frameworks.

IEC 61724 series: The IEC photovoltaic system performance standard series explicitly references simulation methodology aligned with PVsyst’s approach to loss categorisation. PVsyst’s loss diagram structure maps directly to the loss categories defined in IEC 61724-1 (performance monitoring) and IEC 61724-3 (energy evaluation). SAM does not map its output to IEC 61724 categories in any documented way.

MNRE and Indian regulatory context: MNRE tender documents for IPP and KUSUM projects reference yield assessment in ways that assume PVsyst as the simulation tool. When Indian EPCs submit yield reports to SECI or state DISCOMs as part of project development documentation, PVsyst reports are accepted without question. SAM reports would require explanation and potentially a re-simulation request. Our MNRE DCR compliance guide covers the documentation requirements for Indian project submissions in detail.

IFC Performance Standards: IFC Performance Standard 3 (resource efficiency and pollution prevention) references energy yield documentation for solar projects in ways that align with PVsyst methodology. Lenders applying IFC standards (the majority of DFI-funded projects globally) therefore carry an implicit preference for PVsyst reports.

The IEA Photovoltaic Power Systems Programme (IEA-PVPS) has published extensive guidance on performance assessment and bankable yield that references PVsyst methodology throughout. For projects targeting any IEA-member country financing, this institutional alignment carries practical weight.

How Heaven Designs Approaches Tool Selection

Our simulation workflow is structured around client needs, project stage, and lender requirements. Here is how we recommend clients think about tool selection:

• For any project with a term loan, bond, or DFI investment: PVsyst primary simulation, full uncertainty budget, P50/P90 with documented inter-annual variability. SAM cross-check optional but recommended above 10 MW.
• For pre-feasibility screening of 5+ sites: SAM batch analysis first, then PVsyst for the two or three sites that reach financial due diligence.
• For rooftop C&I projects below 1 MW with internal equity funding: PVsyst for yield assurance, no SAM needed.
• For government grant applications (Indian PM-KUSUM, US USDA REAP, World Bank GEF programmes): confirm which tool the programme specifies. Indian government programmes expect PVsyst; US DOE programmes often reference SAM.
• For academic or policy research: SAM is the appropriate primary tool.

Our solar engineering workflow for Indian EPCs covers how simulation tool selection fits into the broader project engineering timeline from site assessment through commissioning.

Additional context on structuring simulation deliverables for lenders is in our guide to outsourcing solar design for EPCs, which includes a section on what bankable documentation packages require from the simulation phase.

For the complete picture on how PVsyst uncertainty is quantified and translated into P50/P90 for lender reporting, our P50/P90 yield report guide covers the uncertainty budget construction methodology step by step.

Verdict Card

Recommendations by Project Type

For utility-scale India C&I and IPP projects targeting SECI, IREDA, or Indian bank financing: PVsyst is mandatory. SAM can add value as a cross-check tool. Our utility-scale solar design service delivers PVsyst primary reports with full uncertainty documentation.

For US residential and small commercial (below 1 MW): Aurora Solar or Helioscope for permit sets; PVsyst for any project requiring lender yield documentation. SAM is useful for USDA REAP grant applications where the programme documentation references SAM.

For African utility-scale projects targeting DFI financing (IFC, AFDB, DEG): PVsyst primary simulation is expected by all major DFIs. Solargis data is preferred. Our solar feasibility study service includes DFI-compatible report formatting with dual-source meteo validation.

For academic research and policy analysis: SAM is the appropriate primary tool. Its open-source model and NREL validation studies make it the standard for peer-reviewed research on solar technology economics.

For pre-feasibility portfolio screening (50+ sites): SAM scripting offers automation that PVsyst cannot match economically. Run SAM for site screening, then PVsyst for the short-listed sites that reach financial due diligence.

Understanding the uncertainty methodology that underpins both tools is covered in our guide to P50/P90/P99 in solar yield reports. For the complete PVsyst simulation workflow from data input to lender-ready output, our guide on common PVsyst errors that affect bankability covers the pre-submission checklist that prevents IE rejection.

Frequently Asked Questions

Is SAM accepted by lenders for project finance?

SAM is not universally accepted. Some US government programme grants (USDA REAP, some DOE programmes) reference SAM, but institutional project finance lenders (banks, DFIs, bond markets) expect PVsyst as the primary tool. Submitting a SAM-only report will typically trigger an IE request for a PVsyst cross-simulation, delaying financial close. The five-criterion bankability test described above explains why PVsyst passes where SAM does not.

Can I use SAM to calculate P90 directly?

Yes. SAM’s built-in Monte Carlo analysis can produce a full production probability distribution from which P90 is read directly. This is more rigorous than PVsyst’s manual root-sum-of-squares approach. However, the output format is not in the IE-standard PVsyst template, so it cannot substitute for PVsyst in a lender submission. The Monte Carlo output can, however, serve as a valuable cross-validation of the P90 derived from the PVsyst uncertainty budget.

What is the accuracy difference between PVsyst and SAM?

For simple flat-ground sites without near shading, both tools typically agree within 1–3 %. For complex sites with 3D shading objects, PVsyst’s detailed shading engine produces results that diverge more from SAM’s simplified shading model. Neither tool is inherently more accurate — accuracy depends on input quality and site complexity. The dual-model approach described in this article is designed to surface and investigate any significant divergence.

Is PVsyst worth the licence cost if I already have SAM?

For any project requiring external financing, yes. The $1,500/year PVsyst licence cost is negligible relative to the cost of delays from IE rejection of a SAM-only report. A single financial close delay of two weeks costs far more than the annual licence in financing costs alone. For internal feasibility analysis only, SAM is a capable free alternative that reduces tooling costs for pre-commitment work.

Which tool handles bifacial modules better?

PVsyst has a more extensively validated bifacial model calibrated against measured data from bifacial fields. SAM includes bifacial simulation but it is less commonly used in IE review workflows. For bankable bifacial yield reports, PVsyst is preferred. The bifacial gain is also one of the loss chain nodes where the two tools diverge most when using the same site and equipment inputs.

Does Heaven Designs use both tools?

Yes. Our standard workflow uses PVsyst as the primary simulation tool for all bankable reports. For projects above 10 MW or those where the client requests additional validation, we run a SAM cross-check and document the comparison in the report. The SAM cross-check is available as an optional add-on to our PVsyst simulation service. For clients doing pre-feasibility screening across multiple sites, we offer SAM batch analysis as a separate service tier before committing to PVsyst for individual site simulations.

Can SAM simulate single-axis trackers as accurately as PVsyst?

SAM includes tracker simulation, but PVsyst’s backtracking algorithm and GCR-dependent shading model are more detailed for utility-scale tracker layouts. For bankable tracker yield studies, PVsyst is the preferred tool. The tracker backtracking algorithm, in particular, affects the balance between shading losses and self-shading at low irradiance angles in ways that PVsyst models at a per-row resolution that SAM does not replicate.

What meteo data source should I use with PVsyst for Indian projects?

Solargis is the preferred meteo data source for Indian projects when working in PVsyst. Solargis provides the lowest stated uncertainty for Indian irradiance data and is specifically referenced by SECI and major Indian banks in their yield report review guidelines. Meteonorm is acceptable for preliminary studies but Solargis is required for final bankable simulations for projects above 1 MW seeking institutional financing.