For the second job–delivering longer-lasting, though less-intense, power–GE is considering a family of exotic high-temperature batteries that use melted sodium metal. GE has developed advanced sodium-metal chloride batteries for a hybrid locomotive project. The battery boasts high-energy storage capacity, but it hasn’t been used as much as lithium-ion batteries have been, in part because the high temperatures rule out its use in laptops and cell phones. But Vlatkovic says the sodium batteries could be less expensive than lithium-ion batteries, and therefore more attractive for bulk energy storage. The batteries, which operate at about 300 degrees Celsius, could be insulated to keep the temperatures high enough inside the battery while also keeping them safe.
Central to GE’s development efforts is creating the control systems required for switching seamlessly between different ways of storing and delivering power. This, as with the company’s work with batteries, will draw on earlier work with hybrids.
Vlatkovic says the effort could be a huge boon to all kinds of hybrid vehicles. “The prime source of energy can be, in principle, anything,” he says. Instead of a small fuel cell, GE could use a small advanced diesel engine running on renewable biofuels or equipped to get the most from new ultra-low sulfur diesel (see “How Diesel Technology Could Cut Oil Imports”).
Such a diesel hybrid may prove to be about as efficient and clean as a fuel-cell-powered vehicle, says Van Amburg, when the costs of making hydrogen are considered. But, he adds, “there’s still room for debate.” GE’s effort is part of a $49 million program funded by the Federal Transit Administration to help make fuel-cell transit buses practical. Hydrogen-fuel-cell-powered vehicles could reduce pollution in cities, since they emit only water, and they have an advantage over battery-only electric vehicles in that refueling times are typically faster. But other options might make more sense from an energy-efficiency or environmental perspective. While fuel cells only emit water vapor, the cheapest ways of making hydrogen fuel use fossil fuels, emitting greenhouse gases in the process. And the manufacture and transport of hydrogen consumes energy, too.