Norwegian energy storage startup Photoncycle has raised €15 million in Series A funding to commercialise its seasonal energy storage technology across Europe. The round was led by NordicNinja and Voima Ventures, with participation from Lifeline Ventures, Eviny Ventures, Luminar Ventures and Momentum.
The company focus to scale a system that allows households and businesses to store surplus renewable energy generated in summer for use during winter months.
What Photoncycle does
Photoncycle is building a distributed energy storage system designed to solve a structural limitation of solar power: seasonality. Solar panels often generate surplus electricity during summer but far less during winter, when heating demand peaks in northern Europe.
The company’s system converts excess solar electricity into solid-state hydrogen, which is stored underground and later converted back into heat and electricity when demand rises. This allows energy generated months earlier to be used during colder periods.
Unlike conventional lithium-ion batteries, which are typically designed for short-duration storage measured in hours or days, Photoncycle’s architecture targets long-duration storage measured in months. The system combines solar generation, an energy processing unit and underground hydrogen storage capable of storing roughly 10,000 kWh of energy for a household installation.
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The company plans to offer the technology through a subscription-style model, bundling solar panels, storage infrastructure, maintenance and energy trading access into a single service. The goal is to lower the upfront cost barrier for households while enabling them to stabilise energy costs year-round.
The €15 million Series A will finance the company’s transition from pilot deployments to early commercial rollout. Photoncycle plans to launch its system initially in Denmark and the Netherlands, two markets with high solar adoption and policy incentives supporting decentralised energy systems.
Moreover, energy storage has become a central component of Europe’s transition to renewable power. Solar and wind generation have expanded rapidly across the continent, but their intermittent nature creates volatility in supply and pricing.
Most current storage technologies address short-term balancing, smoothing fluctuations over hours or days. Seasonal storage remains a far more difficult engineering challenge. In northern Europe, the gap between summer solar production and winter heating demand can span several months.
Europe’s reliance on imported fossil fuels has sharpened interest in solutions addressing this imbalance. In 2025, the EU imported roughly €396 billion in fossil fuels, highlighting the continued dependence on external energy supply even as renewable capacity grows.
Investors have increasingly backed startups exploring alternative storage technologies, from thermal storage to hydrogen and mechanical systems. European energy storage startups have collectively raised more than €2 billion in recent years, reflecting the strategic importance of the sector in achieving climate targets.
Photoncycle’s next challenge is moving from early pilots to commercial deployment. If its technology can deliver reliable seasonal storage at scale, it could help address one of the least discussed bottlenecks in Europe’s energy transition: what to do with summer’s surplus electricity when winter arrives.
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