The final year of the StartSun project is currently underway and now is a good time to reflect on the entire life cycle of the pilot projects.
In each partner country, piloting of energy communities was carried out and a solar power feasibility calculator was developed, and their progress and challenges were discussed in project consortium meetings. In addition, a Start-up Package was built in each partner country to support the establishment and operation of a solar energy community. In addition to Finland, study visits of the project’s solar power sites were organised in Sweden and Estonia.
The Marttila Pilot: From Theory to Practice
In Finland, the StartSun’s pilot project was found through the cooperation with Valonia and their TEMU – Housing Companies Energy Transformation (ERDF) project, which investigated the utilization of energy communities in housing companies. While TEMU’s original objective was to establish a fully functional solar energy community, various real-world implementation constraints led the Green Net Finland (GNF) team to adopt the Marttila site as a ‘hypothetical-practical’ pilot for the StartSun project.
The pilot housing company is a terraced house complex built in the 1990s, consisting of two buildings with three apartments each. In 2024, the housing company reached a turning point and decided to replace its original oil heating system. An air-to-water heat pump system was selected as the sustainable solution. Throughout this transition, future-proofing remained a priority; the property manager actively surveyed various solar energy configurations—evaluating both standalone solar PV systems and integrated Battery Energy Storage Systems (BESS).
Figure 1. Illustrative photo of Marttila (photo from the StartSun project image bank)
The StartSun project set out to clarify the operational framework and conducted preliminary feasibility calculations for the energy community. Through active collaboration, the GNF project team and the Marttila property manager addressed critical implementation details, such as fire safety aspects.
To ensure that these valuable insights were not lost as tacit knowledge, the key takeaways from these discussions, investigations, and calculations were integrated into the Finnish version of the StartSun Start-up Package (available on the GNF’s website). This allowed the general guidelines to be expanded and made more concrete, tailored specifically to the real-world needs identified in the Marttila pilot. By consolidating this essential information, the project provides other housing companies with a practical roadmap, ensuring they can benefit from the lessons learned and achieve success in their own energy community initiatives.
Successes and Challenges
During the project, the Marttila housing company took a decisive step toward sustainable energy use by replacing its oil heating system with an air-to-water heat pump. As the new system consumes more electricity than a traditional oil burner, the transition required upgrading the property’s electrical connection.
While the physical installation of the heat pump was completed swiftly, the commissioning process faced an exceptional delay due to the DSO (Distribution System Operator), which faced grid capacity constraints. Due to this challenge, the commissioning of the heat pump lasted over a year. This bottleneck was primarily driven by the housing company’s forward-thinking strategy: the new connection was intentionally sized to accommodate future electric vehicle (EV) charging infrastructure. Consequently, the existing local grid required extensive technical assessments and reinforcements before the system could be safely energized.
The success of the heating system transition was made possible through the active cooperation of the residents and the property manager. The property’s condition and renovation needs were meticulously studied, allowing for long-term strategic planning. During the process, it was identified that the original roof, dating back to the 1990s, would not be suitable for future solar installations. To ensure safety and longevity, the housing company invested in a full roof renovation following the heating system upgrade. These key lessons and challenges are summarized in Figure 2.
Figure 2. Key lessons learned from the Marttila pilot
Future Outlook
Throughout the renovation process, the property manager’s long-term commitment to the property’s lifecycle was instrumental in evaluating future energy investments, such as solar PV systems integrated with BESS. Rather than seeking quick fixes, the property manager demonstrated exceptional tenacity by systematically addressing complex issues, including fire safety and the critical necessity of a formal commissioning protocol.
Through close cooperation with the project team, the property manager ensured that every technical requirement for the commissioning protocol was meticulously defined. Furthermore, these efforts extended to proactive consultations with the local fire department and insurance providers to clarify all safety conditions and insurance terms. This diligent groundwork ensures that the housing company is fully prepared for safe and compliant technology integration.
Following the successful completion of the roof renovation in the spring of 2026, the property manager’s persistent focus on sustainability has brought the implementation of solar panels into the near-future horizon. A strategic decision was made to exclude BESS from the current plans. This was driven by feasibility calculations showing the unprofitability of short-term storage, but also by a strong sense of fiscal responsibility.
As the housing company is municipally owned and provides rental housing, the property manager highlighted that any additional maintenance burdens—such as the high costs of maintaining a battery system during winter months—would create unnecessary financial strain for the municipality. By prioritizing a cost-effective and low-maintenance solar strategy, the property manager ensured a sustainable path that protects both the public budget and the long-term interests of the tenants.
Ultimately, the property manager emphasized that the most significant benefit of participating in the StartSun project was the transition from uncertainty to a clear, actionable roadmap. The expertise and feasibility calculations provided by the project have empowered the property manager to lead the housing company toward a resilient and carbon-neutral future.
The blog is part of the StartSun project.
Authors: Evilina Vinonen & Riikka Ojala
Project partners: County Administrative Board of Östergötland LP (SE) Lead Partner, Society ”Zemgale Regional Energy Agency” (ZREA) (LV), Estonian University of Life Sciences (EE), Uppsala University (SE), Green Net Finland (FIN), Society ”Green Liberty” (LV), Tartu Regional Energy Agency (EE), Åtvidaberg municipality (SE), Jelgava City municipal institution ”Central Administration” (LV), Jekabpils County Council (LV), University of Tartu (EE), Co-operative Seto Aiad (EE), Kalevipoja Koda Foundation (EE)
Funding: Co-financed by the European Union Interreg Baltic Sea Region programme. Total budget approx. 3.2 M€, of which GNF’s share 240,000 €
Implementation period: 11/2023 – 10/2026