Hybrids make up less than 3 percent of passenger-vehicle sales, largely because they cost so much. Expensive batteries account for much of the premium price, but Riccardo Signorelli is developing cheap ultracapacitors that could replace them. Hybrids based on his technology could be inexpensive enough to start paying for themselves in fuel savings after one to two years.
Ultracapacitors, which store actual electrical charges rather than storing energy chemically, are far more durable than batteries and work well in cold weather. But conventional ultracapacitor cells store only a relatively small amount of energy, so it would be expensive to use them in the quantities required to power a car. Signorelli has developed new ultracapacitor materials that use arrays of carbon nanotubes to form electrodes with a large surface area, tripling the amount of energy that each cell can store. In 2008 he founded a company called FastCAP to commercialize the technology (he is currently CEO), and by now he’s raised $7.6 million. The company has focused on bringing down the high cost of nanotubes through cheap manufacturing techniques based on those used in the solar-cell industry. All told, the ultracapacitors should be able to store energy at less than half the cost per watt-hour of current technology. Signorelli expects that hybrids with his ultracapacitors will start appearing within five years. —Kevin Bullis