What is the RET file format?
A .ret file is a legacy project file created by RETScreen, a free clean-energy analysis tool developed and maintained by Natural Resources Canada (NRCan). Engineers, planners, and policymakers in over 200 countries use RETScreen to model the energy output, costs, and greenhouse-gas savings of projects such as solar PV, wind farms, biomass plants, and building energy-efficiency retrofits.
Internally, .ret files are Microsoft Excel 97-2003 workbooks stored in the OLE2/CFBF container - identifiable by the D0 CF 11 E0 magic bytes. Each file contains multiple spreadsheet sheets representing the project's analysis modules: energy model inputs, local climate data, equipment costs, emission-reduction calculations, and financial viability metrics. All calculations run as embedded Excel formulas and VBA macros, so the file can be opened and inspected in Excel even without RETScreen installed, though the macro-driven analysis will not execute.
The .ret format was in use from approximately RETScreen 2 (circa 2000) through RETScreen 4. The current platform, RETScreen Expert, saves projects as .retx files, making .ret a legacy extension. Because .ret files are structured as XLS workbooks, they remain readable in Excel on Windows or macOS, though full functionality requires the Windows-only RETScreen Expert application.
Security & safety
RISK: LOWRET files are Excel workbooks from a government clean energy tool. The main risk is malicious macros if a .ret file is obtained from an untrusted source (since the file is an Excel workbook that can contain VBA). Always download .ret sample projects from the official NRCan RETScreen website. Legitimate .ret files from NRCan carry no macro risk.
Format details
in a nutshellPrograms that open RET files
Windows2 apps
Microsoft Excel
Paid Open the .ret file in Excel to inspect the worksheets and data - useful if RETScreen is not installed, but analysis macros won't run. 
RETScreen Expert
Free Download RETScreen Expert from NRCan. Open the .ret file; the software may offer to convert it to the current .retx format. 
macOS1 app
Microsoft Excel (macOS)
Paid Open the .ret file in Excel on macOS for data inspection. RETScreen Expert itself requires Windows. Technical details
deep spec| Magic bytes | `D0 CF 11 E0 A1 B1 1A E1` (OLE2/CFBF signature) at offset 0 |
| Byte order | Little-endian (OLE2 CFBF) |
| Container | OLE2/CFBF (Microsoft Compound File Binary Format / Structured Storage) |
| Underlying format | Microsoft Excel 97-2003 workbook (.xls) |
| Compression | Per-stream RLE compression within the CFBF Excel stream |
| Encryption | Optional Excel workbook password protection |
| Typical size | 200 KB - 5 MB depending on project complexity |
| Calculation engine | Excel formulas and VBA macros embedded in the workbook |
| Analysis modules | Energy model, climate data, cost analysis, emissions reduction, and financial metrics (each a worksheet) |
| Platform | Windows (primary); macOS can open via Excel but full analysis requires Windows RETScreen Expert |
| Successor format | `.retx` (RETScreen Expert format, current as of 2026) |
| Developer | Natural Resources Canada (NRCan) |
| User base | 750,000+ professionals in over 200 countries |
| Released | Late 1990s (RETScreen Classic); RET extension used throughout RETScreen 2-4 era |
| Latest version | RETScreen Expert (current); new projects save as .retx - .ret is legacy |
| Specification | natural-resources.canada.ca |
RET conversions
Community Q&A
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