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Intended to develop composite body panels that could store and release energy like a battery, the European Union-funded project STORAGE (2010-2013), led by Imperial College (London, UK) and Volvo Cars (Gothenburg, Sweden), demonstrated a structural supercapacitor roof and a trunk lid with supercapacitor laminates that cut weight 60% compared to existing components. The rechargeable panels comprise multiple layers of carbon fiber/epoxy insulated by fiberglass inserts (see above). Parts were made using Solvay Specialty Polymers' (Woodland Park, NJ, US) MTM47 out-of-autoclave prepreg.

A variety of material approaches were investigated for efficient energy transfer, including carbon aerogel reinforcement of carbon fibers and multifunctional matrices (e.g., 50/50 weight mixtures of epoxy resin and ionic Li salt solution). Volvo claims such panels could power its S80 hybrid demonstrator vehicle’s 12-volt electrical system. Project teammate Swerea SICOMP (Piteå, Sweden) has led patent applications for carbon fiber batteries.

There also has been an increase in car models with photovoltaic solar panels in the roof. “The military has been developing battery panels and embedded solar panels for years,” says Gary Lownsdale, president of Trans Tech International (Loudon, TN, US). “Again, hybrid composite materials offer a lot of opportunity, for example adding carbon nanotubes and other nanomaterials. Embedding flexible electrical circuits in body panels is also an attractive development because you can get rid of the wiring harnesses and simplify the supply chain and assembly.”