The IRENA FlexTool

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Countries exploring ways to ramp up solar and wind energy on their power grids should first conduct thorough flexibility assessments. The IRENA FlexTool performs power system flexibility assessments based on national capacity investment plans and forecasts.

FlexTool assessments reflect full power system dispatch and offer a detailed view of options for flexible generation, demand-side flexibility and energy storage, alongside sector-coupling technologies such as power-to-heat, electric vehicles and hydrogen production through electrolysis.

The freely accessible, user-friendly FlexTool can analyse system operations using a time resolution aligned with real-world system challenges – a resolution of an hour or less in the case of variable renewable energy sources. It also provides least-cost optimisation of the generation mix combined with flexibility solutions for the grid, storage, demand-side response and sector coupling.

The FlexTool is data-driven and follows a relatively broad, general model structure. The user’s initial data largely determines what the model does. The inputs required for a FlexTool simulation include demand, the generation mix, hydrological data, time series for variable renewable sources, interconnections and fuel costs. Transmission data can be divided into separate nodes to reflect real-word power system characteristics.

The FlexTool was developed with the VTT Technical Research Centre of Finland Ltd, with the aim of assisting IRENA members to make a relatively quick yet thorough assessment of potential flexibility gaps, highlighting the most cost-effective mix of solutions to fill such gaps. It is currently the only publicly and freely available (open-source) tool that accommodates both capacity expansion and dispatch variables with a focus on power system flexibility.

Learn more about the tool and how to use it through the new IRENA FlexTool training materials.

Read more about power system flexibility for the energy transition and on IRENA’s FlexTool methodology in this IRENA report. A number of country case studies showcase how IRENA has applied the FlexTool jointly with IRENA Member Countries, including:


flextook chart 
Figure 1 – Flowchart of a simple flexibility assessment with IRENA FlexTool


How the FlexTool works

FlexTool is a linear programming optimisation tool utilising a deterministic model that has perfect foresight. The internal transmission network is represented simply using a transport problem. Power plant aggregation by type is characterised with the most relevant technical parameters. Individual units can also be modelled, but aggregation is recommended to reduce computational time. Maintenance and outages are not considered in the model. In the Investment-expansion mode typically done for a period of 30 years or more, a lower resolution is applied where representative weeks are used for each year in the simulation. Then an operation dispatch at the hourly or shorter time resolution is undertaken to capture flexibility requirements at critical years. The tool does not study issues related to the very short term (second/sub-second scale), such as stability, and does not consider voltage.


IRENA FlexTool training materials

IRENA supports its Member Countries in assessing the flexibility of their power systems. This is a key consideration in planning for high shares of renewables, including maximum use of solar and wind power. The IRENA FlexTool, developed with the VTT Technical Research Centre of Finland Ltd, identifies flexibility trends, gaps and cost-effective solutions to optimise national power systems. The freely accessible, open-source modelling tool reflects both capacity expansion and dispatch variables.
The training materials provided include:

  • Basic training – explaining key features to help new FlexTool users get started.
  • Modelling different flexibility options – demonstrating the tool’s use to address generation, storage and other system challenges.
  • Methodology – examining the underlying mathematical model and answering advanced modelling questions.

Regional training has been delivered in Latin America, ASEAN, MENA and Eastern Europe and Central Asia, getting hundreds of users from IRENA Members and partner institutions started in the use of the FlexTool.

Download IRENA FlexTool