Tonga: Future-Proofing the Grid of an Island State

April 14, 2026

Small island power systems face some of the toughest operational and planning challenges in the world. Demand is growing, diesel generators run continuously with limited opportunities for maintenance, and renewable projects are arriving quickly through public development programs. Yet the teams responsible for operating these grids often do not have access to modern planning tools, flexible models, or the engineering capacity needed to keep pace with change.

During recent technical workshops with Tonga Power Limited (TPL), delivered within an activity supported by the Asian Development Bank, we saw firsthand how open tools can reshape this workflow. For many engineers, it was the first opportunity to build, run, and interpret a full network model of their own system using a platform they could continue to access and adapt after the project concluded.

A first: a full grid model built with open software

Before this work, TPL did not have a complete, reusable power system model. Engineers had attended software courses, but licenses were not always available, and delivered studies rarely included models that could be maintained internally.

Using VeraGrid, our open-source software, we worked with TPL to:

• Build a full network model of the main island system
• Validate generation, load, and network assumptions
• Run steady-state and curtailment studies
• Explore future scenarios with higher renewable penetration
• Train the local team so they could continue developing the model independently

Because VeraGrid is open and includes a user-friendly graphical interface, engineers could install the software themselves, inspect the underlying algorithms, and modify the model without licensing constraints. That created an immediate shift from "studies delivered by consultants" to "studies maintained by the utility."

Faster onboarding through transparency

The openness of the platform made training far more effective. At TPL, staff were able to use the platform to interpret the long-term planning model delivered during the study, something that had not been possible before due to the lack of accessible tools and software licenses.

Because each modelling step is transparent, engineers could ask informed questions, understand the logic behind the results, and troubleshoot issues on their own. That matters especially for utilities that need to make planning decisions while operating with lean technical teams.

Preparing for higher renewable penetration

More photovoltaic systems and batteries are being integrated into Tonga's electricity network. Without adequate models, utilities can struggle to anticipate the impact of these projects on:

• Frequency excursions
• Curtailment
• Minimum diesel loading
• Reserve requirements
• System stability

Using VeraGrid, TPL engineers could run multiple penetration scenarios and visualize the grid response. That helps them assess whether renewable additions improve reliability or introduce new operational risks, and prepare strategies for upcoming projects.

Building sustainable internal capacity

A key objective of this work was to leave behind tools that could continue to be used long after the workshops ended. Open software designed for end users makes that possible. TPL now has:

• A complete, editable power system model
• A workflow for keeping the model updated
• Engineers trained to run studies independently
• A platform that can be shared across departments without license constraints
• A foundation for future initiatives such as centralized control, forecasting, and microgrid studies

For island utilities with limited resources, the ability to retain technical knowledge inside the utility is transformative.

Looking ahead

Tonga is far from alone. Many island states and utilities worldwide face the same combination of rising demand, increasing renewable penetration, and limited modelling capacity. Open, accessible tools can play a decisive role in closing that gap.

At eRoots, we will continue supporting utilities through training, open technical resources, and the ongoing development of VeraGrid. The goal is simple: equip grid operators with the tools they need to plan their own future, run their own studies, and adapt confidently as their systems evolve.

If you would like to learn more about this project or explore how open tools can support your utility, contact the eRoots team.