One Hand Clapping � Blog Archive � Another hydrogen problem

One Hand Clapping � Blog Archive � Another hydrogen problem: "Another hydrogen problem
by Donald Sensing

I cited earlier the engineering problems of widescale use of non-petroleum energy sources or fuels, as explained four years ago by retired engineer Steven Den Beste.

One of those potential fuels was hydrogen, touted somewhat these days as a potential replacement for gasoline in autos and trucks. Not so fast, says Patrick Bedard of Car and Driver. As Steven had pointed out, Patrick repeats that hydrogen is a fuel, but not an energy source. Hydrogen fuel for power cells has to be made from something else but no way of producing hydrogen results in a net gain of energy. It takes more energy to produce hydrogen than the hydrogen yields. Electrolysis, for example, uses electricity to separate oxygen from hydrogen in water, but that electricity has to come from somewhere. Let’s say it comes from a coal-fired electrical plant, since that way of producing electricity is close to the cheapest.

Coal-fired powerplants are about 40 percent efficient, so 140.8 kilowatt-hours of coal energy are required to net the 56.3 kilowatt-hours of electricity to produce our one kilogram of hydrogen. …

Hydrogen gas (at atmospheric pressure and room temperature) containing the same energy as a gallon of gasoline takes up 3107 gallons of space. To make a useful auto fuel, Anthrop says it must be compressed to at least 4000 psi (Honda uses 5000 psi in the FCX; GM is trying for 10,000). The energy required to do that further trims the yield to 17.4 kilowatt-hours. …

So far, the numbers say this: Starting with 140.8 kilowatt-hours of energy from coal gives you 17.4 kilowatt-hours of electrical power from the fuel cell to propel the car, or an energy efficiency of 12 percent.

The upshot of all this is that to make enough hydrogen to replace all the gasoline used by motor vehicles in the US, you’d need to produce 1.16 trillion kilowatt-hours of electrcity. That happens to be almost exactly “twice the energy actually consumed in 2000 with gasoline.”

As Bedard says, if we we had been driving hydrogen cars all along, we’d be frantically trying to invent the gasoline engine.

Related, Glenn Reynolds writes of the fallacy of seeking silver bullets for energy."