Photoncycle raises €15M to scale seasonal energy storage

Photoncycle has raised €15 million in Series A funding to scale its seasonal energy storage system and begin commercial rollout in Denmark and the Netherlands. The funding marks a major step toward making it possible for households to store summer solar energy for winter use — reducing energy bills, lowering dependence on fossil fuels, and strengthening Europe’s energy resilience.

We are excited to share that Photoncycle has raised €15 million in Series A funding to move from full-scale pilot to commercial rollout of our seasonal energy storage system. This milestone allows us to scale manufacturing, expand into Denmark and the Netherlands, and take the next step toward making seasonal energy storage available to households across Europe.

Solving Europe’s winter energy challenge

Europe has made major progress in renewable energy over the past decade. Solar panels are now common across rooftops, and clean electricity production continues to grow. However, one major problem remains unresolved: most solar energy is produced during the summer, while most heating demand occurs in the winter.

This seasonal mismatch forces households to rely on grid electricity and fossil fuels during the cold months. In 2025 alone, the EU imported €396 billion worth of fossil fuels. At the same time, space heating accounts for more than 60 percent of household energy use. As long as energy cannot be stored from summer to winter, households remain exposed to volatile winter prices and imported gas.

Photoncycle’s system is designed to solve this challenge. By enabling households to store surplus summer solar power for use during winter, seasonal storage reduces reliance on imported fuels and strengthens long-term energy resilience.

Bjørn Brandtzæg, founder and chief executive of Photoncycle, said:

“Europe is beginning to solve short-duration storage. The remaining gap is seasonal. If households can store cheap solar powered summer energy for winter use, they reduce exposure to imported fuel and price volatility as well as to increasing grid costs for consumers.”

Scaling manufacturing from 2027

As part of this funding round, we are launching the first phase of our industrial scale-up. Our planned manufacturing facility will reach 1.4 TWh of annual storage capacity at full scale, equivalent to seasonal storage for approximately 140,000 homes, each storing 10,000 kWh of energy. The first phase of this expansion is expected to go live in 2027.

This industrial step is critical. Seasonal storage is not only a product — it is infrastructure. Scaling production capacity is how we move from pilot installations to broad commercial deployment.

A subscription model designed for predictable energy costs

Photoncycle plans to offer the system through a subscription model that includes rooftop solar panels, 10,000 kWh of seasonal energy storage, and full servicing. The goal is to make seasonal storage accessible without high upfront investment.

By storing summer solar energy for winter use, households can reduce their reliance on grid electricity during high-price periods and lower exposure to grid tariffs. The system is designed to reduce total household energy costs by around 30 percent on average, while increasing energy independence. At the same time, it replaces fossil-based heating with locally stored renewable energy, reducing household CO₂ emissions.

Interest is already strong. In Denmark, where energy prices are among the highest in Europe, we have a rapidly growing list of pre-orders. Around 300,000 Danish homes still rely on gas heating systems that are set to be phased out by 2035, creating a clear need for alternatives.

Backed by leading Nordic and international investors

The round was led by NordicNinja and Voima Ventures, with participation from Lifeline Ventures, Eviny Ventures, Luminar Ventures, and Momentum.

Tomosaku Sohara, Co-Founder and General Partner at NordicNinja, said:

“From our perspective of bridging Japanese capital and European startup expertise, we strongly believe energy sovereignty must be strengthened across both Europe and Asia. Photoncycle combines deep technical innovation with a clear, scalable path to global deployment. Long-duration energy storage is critical to building resilient, reliable clean energy systems in Europe, Japan and beyond. We’re excited to help introduce the team to global opportunities, building on our long experience in the energy sector.”

Inka Mero, Founder and Managing Partner at Voima Ventures, said:

“As the share of renewable energy increases, structural price volatility in electricity markets is rising. Seasonal storage is therefore not a niche solution, but a systemic necessity. Photoncycle addresses this imbalance by enabling households to store energy across seasons and reduce their dependence on imported fossil fuels. This is a radically important building block for a resilient and sovereign European energy system.”

Teemu Mattila, Partner at Lifeline Ventures, says:

“As grids move toward high variable renewables penetration, energy becomes abundant in the summer and scarce in the winter. Seasonal storage and reliability become real constraints. Photoncycle is developing technology that thrives in this new reality. It is the world's first residential energy system capable of storing summer surplus energy and dispatching it in the winter while lowering the energy bills of their customers."

What comes next

The Series A funding will now be used to scale manufacturing capacity and support early commercial deployment in Denmark, followed by expansion into the Netherlands and other major European markets. Beyond Europe, we see significant opportunities in Asia and the United States, where similar seasonal energy challenges exist.

Seasonal energy storage represents the next step in Europe’s renewable transition. By allowing households to store energy across seasons, we are building a new layer of distributed energy infrastructure — one that strengthens resilience, reduces fossil dependence, and brings greater stability to energy costs.

If you are a homeowner interested in becoming more energy independent, we invite you to join our waiting list.