Sunlight can also be focused and concentrated by mirrors and the resulting energy employed to heat liquids that drive turbines to create electricity—a technique called solar thermal generation. Existing systems produce electricity at about twice the cost of fossil-fuel sources. Engineering advances will reduce the cost, but solar thermal generation is unlikely to be feasible outside regions such as the southwestern United States that receive substantial sunlight over long time periods.
Many new vehicle technologies have the goal of steering automobiles away from a dependence on fossil fuels. One vision is an all-electric vehicle (EV) that uses no gasoline or diesel fuel and does not emit any CO2. But affordable and reliable EVs will require advances in energy storage. At present, batteries that store enough electricity to give a vehicle acceptable driving range are expensive, large, and heavy. Yet technology may provide new options. For example,
recent advances in nanotechnology, applied to the lithium ion battery, may permit significantly more energy to be stored in a smaller, lighter package.
A compromise—plug-in hybrid electric vehicles (PHEVs)—may secure a significant place in the market sooner. PHEVs have conventional gasoline engines as well as batteries that can supply enough energy to travel 10 to 40 miles, depending on the kind of batteries used. They run on electric power until the batteries are discharged, then switch to gasoline for additional range. As of January 2008, no PHEVs were in production. But several major motor companies—including Toyota, General Motors, and Ford—have plans to introduce PHEVs within the next few years.
EV and PHEV batteries are recharged by plugging them into an electricity source while the vehicle is parked. This provides the immediate benefit of shifting some transportation energy demand from onboard petroleum-based fuels to the electrical grid. However, CO2 emissions would not decline proportionally because about half of the electricity used to recharge the vehicle’s batteries is produced at coal-based plants.
This renewable technology, already widely deployed in 36 states and producing almost 1% of America’s electricity, uses the wind-induced motion of huge multiblade rotors—sweeping circles in the air 100 yards in diameter—to drive emission-free turbines. But like solar energy, the source is intermittent and currently lacks an economically practical way to store its energy output. In addition, the huge wind