Storing energy as heat is a proven pathway to address the challenge solar power faces when it's dark or cloudy outside by enabling the capture, storage and on-demand release of thermal energy. The process, called high-temperature thermal energy storage (TES), however, can be prohibitively expensive. Researchers at Penn State have found that steel slags - a rock-like waste byproduct of the steelmaking process - may potentially serve as a low-cost, heat storage candidate for TES applications.
They published their first-phase findings of a three-phase project today (Sept. 15) in Solar Energy. The first phase focused on identifying the morphological structure of three types slags to evaluate their suitability for thermal energy storage. The eventual goal of this research, the team said, is to reduce slag waste and produce materials that can be used in TES applications.
"One of the problems with many renewable energy sources, like solar, is that they are intermittent," said Olumide Ogunmodimu, assistant professor of energy and mineral engineering at Penn State and co-author on the paper. "Solar energy is inherently intermittent and variable because sunlight is not continuously available due to the day-night cycle and changing weather conditions. This means we need to find some way to store the energy captured from the sun for later use."
Similar to how batteries store energy, TES systems can store thermal energy from hours to weeks and discharge the thermal energy when needed. The researchers tested the properties of three different steel slags - which comprise impurities removed from metal during steelmaking - in phase one of the project to evaluate their preliminary suitability as a candidate material for high-temperature TES applications.
"Despite clear advances, many engineered TES systems still face challenges related to material cost, corrosion and long-term degradation under repeated thermal cycling," said Michael Enemuo, graduate student in mining and mineral processing engineering in the John and Willie Leone Family Department of Energy and Mineral Engineering and lead author of the paper. "These limitations have motivated increasing interest in low-cost, sensible heat storage media, particularly materials derived from industrial by-products."
Enemuo recognized the challenges with TES systems and connected them with his knowledge of slags.
"For me, it started with the waste generated by the steel industry," Enemuo said. "There are piles and piles of slags stored near the steel factories, which can be toxic to the environment, so finding a way to repurpose them was a big motivation."
