Electric cars are part of the vision of a clean energy society, in which Americans would use few fossil fuels, emit limited greenhouse gases and depend less on foreign sources of energy. Will that vision be realized – and are electric cars even necessarily part of that vision? Are electric cars environmentally friendly? Are they an economical means of transportation now? How likely are they to capture the market in the coming years?

The answers to these questions are maybe, yes, no and not very.

What exactly is an electric car?

An electric car is any car that is powered by electricity. It could be powered by an on-board battery or an on-board fuel cell – which itself could be powered by on-board hydrogen. I’ll ignore the fuel cell for now and consider the different types of battery-powered vehicles.

A battery-driven electric vehicle could be a hybrid-electric vehicle (HEV), a plug-in hybrid-electric vehicle (PHEV) or a pure battery-powered electric vehicle (BEV).

A HEV, like the Toyota Prius, has only a small battery, which is recharged by the vehicle’s internal combustion engine running a generator. The Prius’ battery only stores enough electricity to run the car for about five miles. But because of the Prius’ ingenious design, it uses less gasoline per mile than a similar gas-powered vehicle. That is largely because it can shut itself off when idling and can recover energy when the car brakes.

A PHEV is a HEV that can also be plugged into an electric socket to have its battery charged. For that capability to be of much use, the PHEV must have a larger battery than the HEV so that it can run more than five miles on the charge.

A pure battery electric vehicle, BEV, unlike the HEV and PHEV, has no other source of energy than its battery.

The electric vehicle scenario

Electric cars are part of the environmental vision because that vision includes an economy that is not powered by fossil fuels.

The idealized scenario runs like this. In the future, because of the dwindling supply of fossil fuels and climate change concerns caused by their emissions, electricity would be generated from non-carbon-emitting sources. In the usual vision, these sources would be renewable – chiefly wind, solar, hydroelectric and biomass – though they could include nuclear. Because most of the renewable sources generate power intermittently and randomly, some means must be found to store the energy or to manipulate demand so it matches the power generated.

The only economical means of large-scale electricity storage is what is known as pumped hydro. Excess electricity is used to pump water uphill, where it is stored behind a hydroelectric power dam. When more electricity is needed, the water is released through turbines at that dam.

The smart grid is envisioned for large-scale matching of demand to power generation. A smart grid is a region-wide interconnected electricity transmission and distribution network. It is rigged with an enormous number of sensors and controllers, in every household, commercial building and industrial operation. The grid’s sensors and programming can tell when an end use – a water heater, for example, or a refrigerator – can be temporarily shut off without impeding its function, and the grid is able to shut off those appliances when necessary.

This scenario ideally takes care of electric energy use. It doesn’t do anything about oil, however – which is now the principal energy source for transportation and the fossil fuel considered the most limited and geopolitically precarious. Oil is also the second-most carbon-emitting energy source, after coal.