By 2050, more than 80 million tons of decommissioned solar modules are expected worldwide, most of them rich in recoverable silicon. Yet recycling this material has long been hindered by economic and technical limitations.
Researchers at South Korea’s Ulsan National Institute of Science and Technology (UNIST) have now demonstrated a process that not only overcomes those barriers but also links solar waste recycling with clean hydrogen generation—a convergence that could reshape two industries at once.
In a recent study, UNIST scientists succeeded in producing hydrogen from ammonia (NH₃) using silicon (Si) recovered from recycled photovoltaic panels. The process occurs at just 50 °C in a closed, emission-free environment—drastically below the 400–600 °C typically required for thermal ammonia decomposition. Such low-temperature operation not only enhances energy efficiency but also makes the system suitable for decentralized, small-scale deployment, a significant advantage over industrial setups that demand high heat and complex infrastructure.
At the core of the method lies a mechanical reaction within a ball mill, where ammonia interacts with the recovered silicon. This reaction releases hydrogen while simultaneously transforming silicon into silicon nitride (SiN), a high-value compound commonly used in electronic and battery materials. No harmful gases or by-products are emitted in the process, marking a notable step toward circular manufacturing. Crucially, tests showed that recycled silicon performs as effectively as commercial-grade silicon—an outcome that directly challenges assumptions about the inferiority of recovered materials in high-tech applications.
The by-product, SiN, provides an additional layer of economic and technological relevance. Recent evaluations of lithium-ion batteries incorporating this material indicate capacity retention exceeding 80 % after 1,000 charge–discharge cycles. This durability not only supports the expansion of electric mobility and stationary storage but also reduces reliance on critical minerals such as cobalt, whose supply chains remain geopolitically and environmentally vulnerable.
From a cost perspective, the implications are equally compelling. When factoring in the sale of SiN, economic modeling suggests the hydrogen production cost could reach approximately –€6.75 per kilogram. In effect, the process pays for itself—a rare occurrence in a field where most low-carbon hydrogen pathways still depend heavily on subsidies or carbon pricing mechanisms to remain competitive.
The timing of this development aligns with intensifying policy momentum. Both South Korea and Japan are advancing ammonia-based power generation and shipping fuels, capitalizing on the compound’s high energy density and existing transport infrastructure. Yet the challenge has always been releasing hydrogen from ammonia efficiently and cleanly. UNIST’s low-temperature approach directly addresses that bottleneck, potentially accelerating the integration of ammonia as a practical hydrogen carrier.
In Europe, the initiative echoes the objectives of the EU’s Critical Raw Materials Regulation and Hydrogen Strategy, which promote resource recovery alongside green fuel deployment. A process capable of transforming photovoltaic waste into hydrogen and battery materials encapsulates that dual mandate—decarbonization paired with circularity.
