Energy simulation Comparison

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This article is written by the makers of one of them, so each table below also shows where the others are ahead, and the last section lists what V9 does not do yet.

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Industry and Business Oct 6, 2026 5 Add to Reading List

IST PVSolar Simulator, PVsyst 8, HelioScope and RatedPower: An Honest Comparison

The four tools do different jobs, so the right one depends on the project and on who has to trust the result.

PVsyst 8 is the yield study that lenders and independent engineers ask for by name.
HelioScope is the fast, browser-based design and simulation tool for commercial and industrial roofs, mainly in markets where its data and rate libraries are strong.
RatedPower designs utility-scale plants on real terrain and produces their engineering documents.
IST PVSolar Simulator V9 takes a commercial roof from a drone image to a proposal, drawings and a lender file in one project, with Indian costs and taxes built in.

No tool here wins every row. This article is written by the makers of one of them, so each table below also shows where the others are ahead, and the last section lists what V9 does not do yet.

Four tools, four jobs

Each product was built around a different deliverable, and that explains most of the differences that follow.

	IST PVSolar Simulator V9	PVsyst 8	HelioScope	RatedPower
Built for	Commercial and rooftop projects: design, yield, finance and proposal	Detailed energy yield studies	Commercial and industrial design and simulation	Utility-scale PV, battery storage and hybrid plants
Typical project	A factory or warehouse roof, or a small ground area	Any size, where the number will be audited	Commercial roofs and ground mounts	Ground-mount plants of 5 MW and above
Runs on	Web browser	Windows desktop	Web browser	Web browser (cloud)
Main output	One project file feeding report, drawings, bill of quantities, proposal and lender file	The simulation report with its loss diagram	Layout, production report and proposal	Over 400 pages of technical documents per design
Owner	IST Sunpower System, India	PVsyst SA, Switzerland	Aurora Solar	Enverus

A designer rarely chooses between all four. The real choice is usually between two of them for a given kind of project, and the sections below are arranged to make that choice easier.

Energy simulation

On the energy model itself, PVsyst and RatedPower go deepest, HelioScope resolves shade at the finest level on a roof, and V9 sits between an array-level and a module-level method.

	IST PVSolar Simulator V9	PVsyst 8	HelioScope	RatedPower
Time step	Hourly. The 15-minute option interpolates hourly data	Hourly or sub-hourly	Hourly, 8,760 steps	Hourly; its published method also covers sub-hourly steps
Weather data	PVGIS or NASA hourly data. Other providers only as twelve monthly values	Imports hourly and sub-hourly files from the main providers	Built-in typical-year datasets and uploads	The user's own weather, horizon and albedo data, or built-in sources
Near shading	Per area and per string, read at the sun's position each hour. A module counts as lit or shaded at its centre. Objects also reduce diffuse light	3D scene; models the bypass diodes inside a module	Shadow mapped per module, hour by hour	Ray-traced module by module on the real terrain
Electrical model	Each sub-array on its own inverters. One sub-array across two roof faces shares its inverter limit	Sub-arrays and inverter inputs defined one by one	A current-voltage curve for each module	Plant-scale DC and AC losses, cables and transformers

Two rows matter most in practice. Weather data decides whether a lender's preferred source can be used at all. The time step decides how well clipping is counted when the DC array is much larger than the inverter. On weather data V9 is behind all three today. On the time step it is level with HelioScope and behind PVsyst and RatedPower.

Design and layout

Layout is where the tools differ most by project type. RatedPower automates a whole plant on terrain, HelioScope and V9 work on roofs, and PVsyst is a simulation tool, not a design canvas.

	IST PVSolar Simulator V9	PVsyst 8	HelioScope	RatedPower
Starting point	A drone or satellite image traced by the designer; boundary from GeoJSON or KML	A 3D shading scene built or imported for the simulation	Layout drawn in the browser;LIDAR-assisted modelling and automatic obstruction detection on the Pro plan	Site boundary, exclusion areas and topography; the software scans many layouts and picks the best
Rooftop detail	Roof faces, parapets, rooftop objects with heights; shaded modules marked on the plan by cause	Not a roof layout tool	Roof layout with obstructions	Not built for rooftops
Structure and height	3D view with posts, footing blocks and rails; a finder for the mounting height with the highest rear-side gain	Height entered as a simulation input	Racking chosen as a design input	Structures, trackers and earthworks for the plant
Terrain and large sites	Flat roofs and flat ground areas only	Terrain can be imported for shading	Commercial ground mounts	Its main strength: terrain, cable routing, substation
Battery storage	Battery sizing for self-use and peak shaving	Storage strategies in the simulation	Storage modelling on higher plans	Standalone and hybrid battery plants

For a roof, the practical comparison is V9 against HelioScope. HelioScope is ahead on automatic site modelling from LIDAR. V9 is ahead on site detail a designer hands to the installer: parapets, structure, and the shaded modules named by cause.

Documents and finance

This is where V9 is strongest for a commercial project, and where RatedPower is strongest for a utility-scale one.

	IST PVSolar Simulator V9	PVsyst 8	HelioScope	RatedPower
Yield report	Simulation report with loss diagram and single-line diagram	The reference report in the industry	Production report with a loss tree	Energy yield and design reports
Drawings	Wiring diagram, cable schedule with route diagram	A basic single-line diagram	Layout and wiring design	Single-line diagrams, layouts and interconnection reports
Bill of quantities and proposal	Both, from the same project	Outside its scope	Proposals on the Pro plan; reviewers find them weak	Bid documents with cost analysis
Financial model	LCOE, NPV, IRR and payback, plus debt cover ratios tested against a lender's own limits, with a Monte Carlo on returns	Economic evaluation of the simulated plant	Financial modelling on the Pro plan	CAPEX and financial outputs for the plant
Lender file	Bankability report in twelve chapters and a due diligence checklist	Not a stated feature	Not a stated feature	Not a stated feature

"Not a stated feature" means it does not appear in the vendor material reviewed for this article. The reviews linked for HelioScope and RatedPower are published by a company that sells a competing product, so read them with that in mind.

Which one to choose

Match the tool to the project and to the person who must accept the result.

Your project	Best fit	Why
Residential, Commercial or industrial roof, owner-funded or simply financed any type solar project	IST PVSolar Simulator V9	Automatic Layout, shading, drawings, bill of quantities, proposal and lender file from one project, with Indian costs and taxes
The same roof, where the lender's engineer will check the yield	V9 for design and documents, plus a PVsyst report	The engineer expects the named report
Commercial roofs in volume, in a market with good LIDAR and rate data	HelioScope	Fast modelling of the site and per-module shading
Utility-scale plant on real terrain, with or without storage	RatedPower	Automatic layout, terrain, cabling, substation and hundreds of pages of bid documents
Any project where the yield study itself is the deliverable	PVsyst 8	Depth of the simulation and acceptance by financiers
DC array much larger than the inverters, or a strict export limit	PVsyst 8 or RatedPower	Sub-hourly simulation counts clipping that hourly steps smooth out

Many offices will run two of these. The common pair for commercial work is a design-and-documents tool for the daily job and PVsyst for the projects that need it.

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