Since the beginning of the full-scale russian invasion in February 2022, Ukraine's energy system has faced unprecedented challenges. Deliberate attacks on critical infrastructure and power plants have already plunged millions of people into darkness and jeopardised the supply of essential services such as heating and water supply during harsh winters. More than 50% of generating capacity has been damaged, leaving a significant gap between available capacity and demand. In response, the Ukrainian government is seeking to develop decentralised energy production, both from renewables and fossil fuels, to build a more resilient grid. However, public narratives revolve around the priority of nuclear power, and policy development lags somewhat behind in unlocking the potential of distributed generation.

In this landscape, private investment in renewables remains low, whereas investments in new flexible generation and energy storage have faced regulatory constraints. The continuing Russian bombing campaign of the Ukrainian power sector chips away its remaining flexible coal and hydro capacities. Rising energy prices for consumers, all-time low prices for PV stations, and risks of supply interruptions are pushing for rapid deployment of distributed generation on the consumer side. However, with the uncontrolled deployment of non-dispatchable behind-the-meter generation unchecked, it threatens to push the limits of the existing flexibility of the Ukrainian power system into suboptimal and more expensive dispatch in the near future.

Ukraine will face the dilemma of ensuring the security of supply in the short term and managing system growth and new capacity deployment in the long term. Poland's recent history of unmanaged solar growth, which led to significant grid curtailment and instability, can be a useful source of inspiration for how to (not) design power systems and create investment signals and achieve the desired electricity balance.

Our organisation has joined the consortium, which united specialists in energy policy and energy modelling. The consortium is headed by the Instrat Foundation, a Warsaw-based Polish think tank dedicated to strengthening policy and public opinion with open data and research for a fair, green and digital economy. Instrat will bring to the project its experience in modelling RES integration scenarios in Poland, policy advocacy and data work. The Open Energy Transition, is a think tank focused on developing models for energy system planning and uniting experts from around the world responsible for building energy system models.

The practical result of our work will be the creation of an open-source power system model PyPSA-UA, which will be integrated with a larger similar model for the entire energy system of Europe. We will be developing Ukrainian expertise in modelling and establishing grounds for a series of data-driven research aimed at providing an independent and professional view of the risks and opportunities for the Ukrainian energy sector. We believe that the development of the model of the Ukrainian energy system based on the PyPSA open-source code and the research based on it will:

• contribute to the critical analysis and policy development process in the energy sector;

• create an accessible tool for energy experts to collaborate with;

• to raise the level of discourse, as well as the possibility of an independent view on a sector.