Amsterdam-based Moonwatt has developed a new type of battery storage system based on sodium-ion NFPP chemistry, purpose-built for seamless solar hybridization. The system integrates battery enclosures with hybrid string inverters, enabling efficient DC-coupled solar-plus-storage integration.

The company gained attention in March 2025 when it raised $8.3 million in seed funding to accelerate growth. Moonwatt operates as an energy storage system integrator, designing, developing, and supplying string battery enclosures, hybrid string inverters, and battery management and site control systems, while sourcing sodium-ion cells globally.

“Initially, we’re sourcing them from Asia, but we aim to add American and European cell sourcing options as soon as they become available and create value for our customers,” Valentin Rota, co-founder and CCO of Moonwatt, said in an earlier interview with ESS News.

Moonwatt’s approach allows it to customize product designs for individual projects and client needs – something traditional “cookie-cutter” container solutions cannot achieve. Unlike legacy systems, Moonwatt’s batteries are distributed across the PV plant, rather than sitting in a single corner.

This modular architecture minimizes land use and can be installed virtually anywhere, including directly beneath solar panels. Its lightweight design enables quick deployment with a standard forklift and eliminates the need for foundations. The architecture mirrors the scalability of solar string inverters, allowing projects to expand from kilowatts to gigawatts – suitable for both new-builds and retrofits.

Because of its decentralized design, Moonwatt can position batteries close to PV panels at low-voltage DC, removing the need for an additional MV transformer. This fully DC-coupled setup reduces electrical balance-of-plant costs, increases efficiency by avoiding unnecessary AC/DC conversions, and enables charging from clipped solar energy, maximizing asset utilization and revenue. Lower PV curtailment translates to higher PV-to-battery-to-grid efficiency, allowing projects to sell more kWh to the grid.

“We mutualize a lot of the solar project balance-of-plant costs – cables, switchgear, transformers – so customers don’t need to ‘double’ the infrastructure for solar and batteries. Overall, this lowers PV capex,” Rota explained.

Moonwatt has also developed an innovative thermal management system with no moving parts. According to the company, such design esnures silent operation, minimal maintenance, and strong protection against dust, water, and air ingress.

By eliminating complex HVAC systems, O&M costs are significantly reduced while reliability in harsh outdoor environments is improved, the start-up claims. As a result, the system can operate for “extended periods at very low or very high temperatures with minimal degradation”.

The company plans to deploy its first project in 2026 at Cleantech Park Arnhem in the Netherlands, in partnership with IPKW and Veolia.

“Sodium-ion technology gave us the freedom to design a fundamentally different product: passively cooled, distributed, safer, and more efficient. We are excited to deploy this innovation, which we believe will transform the BESS sector just as solar string inverters replaced central inverters. This approach helps further reduce the cost of firm solar power,” said Guillaume Mancini, CTO at Moonwatt.

Moonwatt has also secured a €1.15 million DEI+ grant from the Dutch Business Agency, recognizing its development work and the innovativeness of its technology.