Silica sand as thermal energy storage for renewable-based hydrogen and ammonia production plants

Abstract

Due to rising climate change concerns, developing renewable energy and low-cost utility-scale energy storage technologies has become critical to reducing environmental impacts. Thermal energy storage (TES) systems offer scalable, efficient, and low-cost methods for energy storage, yet commercially have mainly been limited to use in concentrating solar power plants. With increasing renewable energy developments, the commercialisation of standalone TES systems has become vital. A few recent studies began exploring sand’s use as a TES material. Sand, particularly Silica Sand, provides an abundant, thermally stable, and low-cost method for storing thermal energy at temperatures as high as 1,200 °C. When there is insufficient electricity to meet demand, the stored heat could be discharged from the silica sand and converted into electricity by driving an electric power system. The silica sand in the Sultanate of Oman was found to be ultra-pure (>98 wt% SiO2); a composition National Renewable Energy Laboratory (NREL) has proven to have ideal thermal properties for its use as a TES system. NREL has also proposed a standalone sand-TES concept, which offers ample storage capacities, longer discharging hours and meagre cost compared to other commercial energy storage technologies. This research analyses the economic benefit of utilising this sand TES system in maintaining the full-day operation of a 500 MW solar-based green ammonia production plant in Duqm-Oman and compares it to commercial lithium batteries. The result shows that using silica sand as a TES system significantly reduced the unit production cost of green hydrogen and green ammonia by 59 % and 48 %, compared to the use of lithium-ion batteries, where the green hydrogen and green ammonia lifetime normalized costs fell to 0.60 US$/kgH2 and 0.16 US$/kgNH3. The sand TES system is thus a promising solution for intermittent renewable energy storage. The low cost and abundance offered through a sand TES system will contribute to ramping up renewable energy projects, thus driving down the costs of clean energy and renewable energy-based products.