It’s starting again. Every few years, these ideas pop up again and at first they appear breathtakingly simple and intuitive. We can run cars on air! We can run them on water! We can forget about batteries for electric vehicles and simply grab wireless power from the road itself.

Everybody loves these ideas, and blog posts like this one that talk about the tech get a lot of hits. But none of it ever gets commercialized. Why? It’s not because the concepts don’t work — they do — but because they’re impractical and expensive, and more mundane ideas are better suited to mass adoption.

The electric road

This one goes back nearly 100 years, and they were toying with it at the 1939 World’s Fair. It’s come up again because Toyohashi University of Technology and the Taisei Corporation in Japan have done a demonstration of what Japan Times describes as “the world’s first electric vehicle that runs without a battery, using special tires that draw power from an electrified road surface.”

solar roadEven Fido loves the solar road. But can we afford it? (Photo: Solar Roadways)

It’s hardly the first. For instance, in 2011, I wrote a piece for the New York Times on Scott and Julie Brusaw’s Solar Roadways:

In concept, the Brusaws’ energy-capturing road is a series of strong glass panels that motorists drive on. Embedded in each panel are solar cells, LED lights--which can spell out messages to drivers and pedestrians — sensors, microprocessors and even heating elements to prevent the accumulation of snow and ice. In a telephone interview, Mr. Brusaw said the road would pay for itself by generating as much as 3.34 megawatt-hours of electricity a day from each lane mile, based on four hours of daily sunlight.

I loved the idea, and the road is very cool-looking — you can even embed traffic messages in the surface via LED lights — but even if it could generate some revenue in operation, it would be prohibitively expensive to build per-mile. Retrofitting every mile of interstate would bankrupt the U.S. Treasury, unless they can figure out a pay-as-you-go scheme.

The Brusaws have made some headway. They raised more than $2 million in an Indiegogo campaign, and last year got their third Department of Transportation grant. But the technology is still not ready for prime time; now they’re studying “freeze-thaw cycling, moisture conditioning, shear testing, and advanced loading (simulates several years of heavy truck abuse in a matter of months).”

Electric roadways are still a while off, though commercialized wireless EV charging will be with us next year. Baby steps.

Air cars! Still blowing in the wind

A French company, Motor Development International (MDI), went viral with a brilliant idea: powering cars on compressed air. Forget gasoline! Forget electric cars! Again, I wrote a skeptical piece for the New York Times. Unfortunately, it takes a lot of energy to compress the air, and storage is such a problem that range is unlikely to be more than 10 or 15 miles.

air carThe MDI air car was supposed to be made in American factories by 2011. We're still waiting. (Photo: Motor Development International)

But the company was undaunted by the skeptics and forged a relationship with India’s Tata Motors (which now owns Jaguar and Land Rover), and made even more extravagant claims. A new and improved model with an onboard heater would travel 848 miles on a tankful of air (106 mpg). Factories would open in the U.S. in 2010, maybe 2011. We’re still waiting.

Again, it’s not a new idea. Back in 1960, aircraft company Curtiss-Wright played around with an air car that worked rather differently — big gas engines powered fans to lift the car off the ground. The military tried out a pair of the prototypes, but deemed them impractical on anything but perfect road surfaces. A consumer version called the Bee never went beyond the design stage.

Water cars: Too cheap to meter?

Yes, it is possible to drive around with a thankful of water to power your car. How does it work? Through electrolysis, hydrogen can be extracted from H2O, and that can power a fuel cell. But there’s a reason all the hydrogen fuel-cell cars on the road now (from Toyota, Honda and Hyundai) instead carry tanks of compressed hydrogen.

water carThe Japanese Genepax car was going to revolutionize transportation by running on tap water. (Photo: Genepax)

Water is heavy, that’s problem No. 1. And then there’s the need to carry around an expensive and delicate electrolysis apparatus. Nevertheless, in 2008, a Japanese company called Genepax showed off a water car and got a lot of mileage out of it. Popular Mechanics made the basic issues plain:

There is energy in water. Chemically, it's locked up in the atomic bonds between the hydrogen and oxygen atoms. When the hydrogen and oxygen combine, whether it's in a fuel cell, internal combustion engine running on hydrogen, or a jury-rigged pickup truck with an electrolysis cell in the bed, there's energy left over in the form of heat or electrons. That’s converted to mechanical energy by the pistons and crankshaft or electrical motors to move the vehicle.
Problem: It takes exactly the same amount of energy to pry those hydrogen and oxygen atoms apart inside the electrolysis cell as you get back when they recombine inside the fuel cell. The laws of thermodynamics haven't changed, in spite of any hype you read on some blog or news aggregator. Subtract the losses to heat in the engine and alternator and electrolysis cell, and you're losing energy, not gaining it—period.

If you’re conspiracy-minded, a fuzzy YouTube video claims that a water car tinkerer named Stan Meyer (he built some kind of fuel-cell dune buggy) turned down “a billion dollars” for his patent, then got murdered. (You can watch that fuzzy video here.) Unfortunately, a court debunked the technology, and the distinguished science publication Nature wrote:

Its not easy to establish how Meyer's car was meant to work, except that it involved a fuel cell that was able to split water using less energy than was released by recombination of the elements ... Crusaders against pseudoscience can rant and rave as much as they like, but in the end they might as well accept that the myth of water as a fuel is never going to go away.

So no water or air cars, and no solar roads? Unfortunately not. We can power our vehicles with internal combustion, batteries or fuel cells. Nothing else looks practical from where I sit. Here's some "amazing" water car video:

Jim Motavalli ( @jmotavalli ) writes about cars, technology and the environmental world to anyone curious enough to ask.