Design and Control of a Translating Drum Spooling System for Gravity Batteries: A Collaboration with Renewell

Climate change and ensuring a clean, long term energy supply are two of the most pressing challenges faced by society. In order to shift to a sustainable energy supply, energy storage technologies must be prioritized and innovated. Renewell Energy proposes a solution of repurposing abandoned oil wells into gravity batteries, which serve as energy storage systems. Renewell operates by using excess clean energy to drive a motor that lifts a heavy weight. When there is energy demand that outpaces supply, Renewell returns energy to the electric grid by lowering the weight and converting the gravitational potential energy into electricity. Renewell’s present winching system– responsible for spooling and unspooling cable to lift and lower the weight– incurs a lot of wear and cost to Renewell’s technology. High costs and excessive cable wear prevent Renewell from becoming a viable long-term energy storage solution since energy storage requires longevity in order to become profitable. Our project reimagines cable spooling to reduce wear on the rope– thereby increasing its longevity– and reducing the infrastructure footprint and cost. In contrast to traditional industrial spooling which bends a rope onto a winding drum from a distance, we translate the drum itself in order to accomplish neat, controlled spooling. To test this system, we scoped the infrastructure for a loaded full-scale winch, we prototyped a scale model to test spooling across a translating drum, and we designed a feedback control system to meet the required precision for cable spooling. To quantify the performance of our winching system, we conducted spooling tests and used a number of measurements to verify our system’s precision using image analysis, encoder readings, and spooling time. From our ⅕ scale model we determined that we achieve the necessary precision for neat cable spooling, with even greater promise on a full scale system, since the acceptable margin of error grows with larger cable dimensions. The implications include an estimated $70,000 in cost savings. In the future, this system would benefit from testing in a full scale or loaded configuration, to uncover any complicating dynamics of spooling large, tensioned cable. Further fine tuning of the controls during motor accelerations can help reduce the error in position to further reduce cable wear. In total, we successfully de-risked an innovative spooling method for Renewell’s Gravity Wells, with significant improvements to the cost and efficiency of their system. This innovation is an important step in energy storage systems for a greener, climate-conscious future.