Riccardo Signorelli, first a graduate student and later a postdoc in Schindall's lab, developed a way to replace the activated carbon with vertically oriented nanotubes. This significantly increases the surface area and voltage of an ultracapacitor electrode, which in turn boosts the amount of energy that an ultracapacitor can store. Schindall's group hopes to develop ultracapacitors that can store five times more energy than those on the market now, bringing their capacity up to one-quarter of the amount stored by lithium-ion batteries. Because ultracapacitors can be charged and discharged thousands of times more than a rechargeable battery, however, Schindall and Signorelli believe that reaching that goal would make ultracapacitors a viable and cost-effective solution for hybrid vehicles. In fact, hybrid buses and heavy-duty vehicles are the first market FastCAP plans to target.

Signorelli cofounded FastCAP to commercialize the nanotube-enhanced ultracapacitors, and he is the company's president. While working at MIT, he has demonstrated electrodes that deliver the power density that the company pitched in its ARPA-E grant application. The ARPA-E grant, he says, will enable FastCAP to complete the process of putting the electrode into a packaged device that operates as predicted. Additionally, by the end of the grant term he plans to have determined the process that will be used for manufacture, built a pilot-scale production plant, and tested the devices in vehicles. Signorelli calls the ARPA-E grant "instrumental" to achieving these plans.

In the longer term, Signorelli also sees a role for FastCAP's ultracapacitors providing short-term buffering to protect the electrical grid against sudden spikes in energy supply or demand. Currently, utility companies are required to maintain what are known as "spinning reserves," which are turbines that are already running, so that when there are sudden surges in demand--say, on a hot summer day--the turbines can provide the extra electricity almost instantaneously. Ultracapacitors distributed throughout the network could provide a few minutes of reserve capability locally, without requiring utilities to burn fuel in a turbine to keep it spinning. That would not only decrease fuel requirements and carbon-dioxide emissions, Schindall says, but also allow companies to use the grid closer to capacity. If we could use the grid just 5 percent closer to capacity, he says, it would save billions of dollars in infrastructure investment.

Ultracapacitors could also ease the integration of renewable energy sources such as solar and wind power, which by their nature are intermittent. Without a way of instantaneously buffering energy from these sources, they could cause region-wide blackouts and will never be reliable enough to rely on exclusively.