Elastomer flywheel energy store

Abstract

The flywheel has been used for centuries as a cheap short-term energy store. The modern machine is an efficient and adaptable piece of precision engineering, but at the price of increased complexity and cost. The new concept presented here is simpler and, hopefully, cheaper. It exploits the nonlinear expansion of an elastomer ring together with its variable moment of inertia. The combination of elastic and centrifugal energy results in a remarkable energy-speed characteristic that allows the extraction of around 80% of the stored energy for a speed variation of only a few per cent, against a drop of more than 50% for a conventional flywheel. Operating in this optimal mode, the elastomer machine has a lower energy density (∼ 4 Wh kg −1 at best) than its metallic equivalent. However, without allowing for its special characteristics, it is expected that the low cost of, for instance, natural rubber could make the elastomer flywheel competitive with existing machines. Beyond the optimal operating regime, the improvement in performance is less, but this is compensated by possible energy densities in the range 10–30 Wh kg −1.