Failsafe Design for Gravity Energy Storage Systems in Idle Oil & Gas Wells

Renewable energy will be crucial to reversing and avoiding the catastrophic consequences of climate change. The intermittent nature of wind and solar energy provides a hurdle to this transition, however, Renewell, a novel start-up, has developed an energy storage solution. Their system uses excess energy to raise a weight up to 100 tons inside inactive oil wells and then lowers the weight to release the stored energy to the grid when needed. Team Failure is Not an Option were tasked to conceptualize and design the critically important failsafe mechanism to prevent the weight from falling into, and subsequently releasing, the toxic chemicals that lie at the base of the well in the case of a system failure.

Our team successfully conceptualized, prototyped, and tested a scaled-down failsafe mechanism for the Renewell system which can later be scaled up to meet larger well sizes. Our failsafe system prioritizes a factor of safety of 7, following the standard in mine shaft and elevator construction, and a maximum efficiency loss of 2% put forward by our liaisons to ensure profitability. Through our calculations, we uncovered a cubic relationship between the size of the fluid filled space between the weight and internal well structure (annulus size), and the speed of the weight. Our prototype reduces this annular gap using an airbag deployed through a bistable trigger mechanism activated by a speed sensitive parachute to significantly slow down the weight. The purpose of our testing was to verify the ability of our prototype to consistently slow down the weight as we increased the mass of the system. Our results indicated that our failsafe system successfully reduced the speed of the falling weight by approximately 4.5 times our control speed with no failsafe system. These relationships evidence the potential for our concept to be scaled up to meet larger well dimensions and employed as a failsafe mechanism for the Renewell system.