Moonwatt, a Netherlands-based energy storage developer, is addressing this challenge with a purpose-built sodium-ion battery energy storage system (BESS) engineered for hybrid solar applications. Moonwatt’s modular “string battery” design combines sodium-ion NFPP cells in passive-cooled, hermetically sealed enclosures with hybrid inverters, enabling DC-coupled integration directly with solar panels. The BESS design eliminates active cooling and high-maintenance HVAC systems, lowering O&M costs and maintaining performance in extreme temperatures. By addressing CAPEX, OPEX, efficiency, and fire-safety concerns, Moonwatt aims to accelerate the adoption of firm solar power. Recognizing the system’s potential to advance solar hybridization, the Dutch Business Agency (RVO) awarded Moonwatt a €1.15 million DEI+ grant to support ongoing development.