PVsyst vs SAM (NREL): Which Is Bankable for Yield Studies

Two tools dominate solar yield simulation discussions in 2026: PVsyst, the Swiss commercial platform most independent engineers use, 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 some independent engineers recommend for large utility-scale projects. (For SAM on its own terms, see our SAM review.)

Quick answer. PVsyst is the industry standard for bankable yield reports because independent engineers and lenders have reviewed its output format for over two decades. SAM from NREL is free and strong for screening, research and cross-checks, but SAM-only reports usually draw an IE request for a PVsyst run. The best 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.

PVsyst’s Professional licence is CHF 700 (about $850) per year (PVsyst shop, 2026). It runs only on Windows. Its models are documented in PVsyst’s help files and discussed widely in academic and industry validation work.

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 the 1990s, and its results have been compared with measured production across many plants and climates. 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 spread to global project finance via European DFIs and banks.

Module and inverter databases: PVsyst maintains a large 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 market.

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

| Lender acceptance | Near-universal | Limited / edge cases | | Learning curve | Moderate | Moderate-to-high | | Scripting | Limited | Full LK scripting | | Multi-technology | PV (with storage) | PV, wind, CSP, storage |

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

Some independent engineering firms 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 (extra simulation time) but reduces the risk of IE pushback 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 can add a SAM cross-check to a PVsyst report on request. For projects above 10 MW, we recommend it when the lender’s IE is known to run its own cross-check.

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: some DOE and development-agency programmes reference SAM for renewable energy analysis.

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 workflow gives it an advantage, since Solargis is among the lowest-uncertainty irradiance datasets for India. 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, often within a few percent for the same weather file. A deeper look at how shading analysis tools model these losses is in QBits Energy’s guide to solar shading analysis software.

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: IEC 61724-1 covers performance monitoring and IEC 61724-3 covers energy evaluation of operating plants. Neither standard mandates a particular simulation tool, but PVsyst’s loss breakdown is easy to reconcile with the monitored categories, which helps when operating data is later compared with the model.

MNRE and Indian regulatory context: In Indian practice, PVsyst is the default tool for yield reports submitted with SECI and DISCOM project documentation; SAM reports would likely need explanation or a re-simulation. Our MNRE DCR compliance guide covers the documentation requirements for Indian project submissions in detail.

The IEA Photovoltaic Power Systems Programme (IEA-PVPS) publishes guidance on performance assessment and yield uncertainty that applies whichever tool you use.

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 generally expect PVsyst; some US DOE programmes 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 effectively 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, see SurgePV’s comparison of the top solar design platforms for how these tools stack up on the layout and permitting side, with 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 major DFIs in practice. 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 CHF 700/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’s bifacial model is more widely used and reviewed in IE workflows. 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?

Our standard workflow uses PVsyst as the primary simulation tool for bankable reports. Where the client or lender asks for extra validation, a SAM cross-check can be added and documented in the report.

For alternatives to SAM itself, see our SAM alternatives guide.

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 is among the lowest-uncertainty irradiance datasets for India and is widely used for lender-grade work. Meteonorm is acceptable for preliminary studies; for final bankable simulations above about 1 MW, confirm the lender’s preferred source.