First Distributed Sodium-Ion Battery System for Hybrid Solar Power Plants
Moonwatt has commissioned its first distributed, passively cooled sodium-ion battery energy storage system (BESS) coupled with a ground-mounted solar power plant in Arnhem, Netherlands. The system uses Moonwatt's proprietary passively cooled battery technology.
It is said to be the first installation ever where a storage system is directly coupled with a ground-mounted solar power plant. The facility operates both AC-coupled and DC-coupled inverter topologies side by side, proving both electrical architectures in field use with the same Moonpods.
In a DC-coupled configuration, the battery is connected directly to the PV generator via a common hybrid inverter; in an AC-coupled configuration, the battery and PV generator each use their own inverters. The same product covers both topologies, making it suitable for both new installations and retrofitting of existing solar plants.
The 500 kWh project operates under real grid conditions and distributes solar energy throughout the day rather than only when the sun shines. Commercial-scale deployments across Europe begin in early 2027.
Performance: Longer Life, Higher Efficiency
Cycle Life
The Moonpod, thanks to its sodium-iron-phosphate-pyrophosphate (NFPP) cells, is designed for 12,000 cycles at 100% depth of discharge. Conventional lithium-ion systems, typically based on lithium-iron-phosphate (LFP), deliver around 7,300 cycles.
The crystalline structure of NFPP is more stable, resulting in lower degradation per cycle and longer reliable operation before capacity replacement thresholds are reached. For a daily cycling solar plant that also provides grid services, this is the difference between replacing the system within the plant's lifetime or not at all.
Efficiency
Since the Moonpod is passively cooled, it consumes no auxiliary energy to keep itself running, and its DC-coupled architecture removes conversion steps. The result is a reduction in energy lost per cycle by up to 25% compared to conventional actively cooled lithium-ion systems, according to the supplier. As batteries become larger and longer-duration relative to the PV they serve, each saved energy unit translates directly into shifted energy and revenue over the plant's life.
Temperature Range
Sodium-ion cells cycle efficiently over a wide ambient range without active thermal management, from low winter temperatures to high summer conditions, with minimal power variation and no efficiency loss on hot days. Conventional lithium-ion systems require active cooling to keep cells near 25°C and lose efficiency on the hottest days, precisely when a solar plant generates the most.
Operation: Less Maintenance, Less Replacement
Moonwatt's proprietary passive thermal management means the Moonpod has no moving parts and no active cooling. This eliminates the main causes of unplanned downtime in field-deployed batteries: cooling pump failures, HVAC degradation, fan replacement, and refrigerant leaks.
- No scheduled cooling maintenance: no coolant refills, no filter changes, no HVAC service contracts.
- No auxiliary power: the system draws nothing from the grid to remain operational.
- Hermetically sealed: IP68 certified against dust, water, and air ingress, designed for outdoor operation in any European climate.
- Swap instead of open: a defective unit is replaced like a string inverter and repaired off-site, so modules are never opened in the field.
Site Selection and Permitting: Smaller, Safer, Quieter
Passive operation means the Moonpod runs silently, important for locations near residential areas or under noise regulations. The enclosure is compact at 1.2 m height and can sit under the panels or next to the generator, distributed across the site in any layout that fits the project.
The distributed approach also carries lower thermal and fire risk than a conventional container system, with an order of magnitude less stored energy per unit and greater spacing between units to prevent propagation. Together, the smaller form factor, silence, and distributed approach make fire and noise permitting significantly easier than for conventional lithium-ion containers.
