Marttila (FI)

Numbers at a glance – modelled projections

• 12 kW solar PV + 10 kW modelled battery storage.
• Estimated annual production of 8 500 kWh/year.
• Estimated annual savings of approximately €1,400/year.
• 510 kg CO₂ avoided per year.
• Total modelled establishment cost of €19,000 (PV + BESS).

The journey of the Marttila Pilot Site

The Marttila pilot emerged through cooperation between StartSun and Valonia’s TEMU project, which had already been examining how Finnish housing companies could benefit from energy communities. The original aim was a fully operational solar energy community, but real-life implementation constraints led the Green Net Finland team to use Marttila instead as a practical testing ground for frameworks, feasibility and decision-making.

The site itself was a realistic test case: a 1990s housing property moving away from oil heating toward an air-to-water heat pump, which increased electricity demand, with future needs like EV charging also factored in. Rather than relying on general enthusiasm, the pilot’s core work was modelling – concrete figures on investment costs, expected savings, payback time, risk and how benefits would be distributed. That modelling did double duty: it made the concept understandable to board members and decision-makers, and it sharpened the plan itself, including the finding that a battery wasn’t financially justified at this scale.

Technical barriers slowed things further. The local grid needed reinforcement to handle the new heating load and future demand, causing roughly a year and a half of delay. The existing roof wasn’t structurally suitable for solar panels without renovation first, and fire safety requirements added further complexity. Existing housing-company debt from other renovations also made financing harder, even once the technical side was in order.

A strong case, waiting on funding

Marttila’s team has built a well-modelled case for what an energy community at the region could achieve – from realistic savings figures to a clear-eyed assessment of where a battery would and wouldn’t make financial sense. What stands between that plan and installation isn’t a lack of readiness on the team’s part, but funding: like many housing companies, Marttila currently lacks the financial capacity to move ahead alone, even with a sound case behind it. The work done so far means that when financing does come together, the path forward is already mapped out – assess the property, calculate the case, and only then ask for a decision.