Friday, December 08, 2006

Hydrogen is Still Stupid

Not long ago BMW announced its new Hydrogen 7, which can run off either hydrogen or gasoline. For the time being, only a limited number are being produced and given to celebrities, presumably to gin up publicity. But the idea is that if and when such a car goes into mass production, consumers won't have to wait for the hydrogen economy to provide a hydrogen refueling station at every corner before buying and using a hydrogen car. Neat idea, right?

Before going into details, let's review a couple of things: First, the hydrogen is being burned in an internal combustion engine. Not a fuel cell. Fuel cells are very efficient, ICEs not so much. Secondly, the hydrogen is being stored on-board in liquid form. Yes, liquid hydrogen. It takes about 50% of the energy contained within the hydrogen itself to cool it down to that temperature, plus half the tank will boil off within 9 days as the temperature slowly rises.

For all that, how much fuel does it consume? This article in Der Spiegel tells us:

The Hydrogen 7's standard combustion engine has been adapted to run on both liquid hydrogen and regular gasoline as well -- and tons of it. The company says the car will consume an average of 13.9 liters (3.7 gallons) per 100 kilometers (roughly 17 miles per gallon) using regular gasoline and a whopping 50 liters to drive the same distance when fuelled by hydrogen.

In other words, BMW has created an energy-guzzling engine that only seems to be environmentally friendly -- a farcical ecomobile whose only true merit is that of illustrating the cardinal dilemma of a possible hydrogen-based economy.

Yeeeoouch! Not only does it get lousy gas mileage, it consumes nearly 4 times as much hydrogen to go the same distance. That's because hydrogen, even when liquefied, has only one-fourth the energy per unit volume of gasoline. So the car has a massive 45 gallon cryogenic tank in order to hold all that hydrogen. And as large as the tank is, it only takes you 125 miles. And at current market prices for liquid H2, that 125 mile trip will cost you about $76.

Burning hydrogen in an ICE doesn't save much (if any) energy compared to gasoline. In fact, using hydrogen in this context is extremely inefficient. Let's assume that the energy to make the hydrogen actually comes from clean alternatives as BMW's promotional material misleadingly suggests. Being very generous, we'll assume an electrolysis efficiency of about 70%. Then 50% gets lost to liquefaction. Then another 10% for boil-off. By this point we've already wasted more than two-thirds of the energy. Then being very generous, we'll assume 40% efficiency of the ICE, in which case less than 13% of your original energy actually gets used to push the car forward.

Instead of going that route, let's say we used the electricity generated via clean renewables to charge a battery, and we used the battery to drive an electric motor. The battery would lose less than 10% of the energy through charging and discharging, and the electric motor is about 80% efficient. That means an overall efficiency of 72%, over five and half times better than burning liquid hydrogen in an ICE. Unless you want to build 5.5 times as many wind and solar farms, the electric car makes a lot more sense. Five and half times as much sense.

Speaking of wind and solar farms, this isn't where the hydrogen to power the Hydrogen 7 is coming from anyway:

And so, in creating the Hydrogen 7, BMW is announcing a future of putatively clean, full-throttle driving. The new car caters to the pleasing fantasy of customers spoiled by high-horsepower engines: That they can conform to ecological standards without making any sacrifices, burning "clean" fuel to their heart's content. Advertizing images display the Hydrogen 7 against a backdrop of wind turbines and solar panels.

But the image is one of deceit. Because the hydrogen dispensed at the new filling station is generated primarily from petroleum and natural gas, the new car puts about as much strain on the environment as a heavy truck with a diesel engine. Add the loss of environmental benefits involved in the production and transportation of the putatively clean fuel to the consumption of the car itself and you get an actual consumption corresponding to considerably more than 20 liters (5.3 gallons) of fossil fuel.

There's really not much sense in even thinking about hydrogen until a such a point where we can produce large amounts of clean energy. Even if using hydrogen is an environmentally sensible thing to do, it's not environmentally sensible until after we've used clean energy to phase out coal. Using it to produce hydrogen entails a fairly large opportunity cost.

Now to be fair, because BMW is using an ICE instead of a fuel cell, they're making it far less efficient than it has to be. If they were to use a fuel cell to drive an electric motor, they would probably lose about 20% from the fuel cell and another 20% from the electric motor, meaning that they would waste "only" 80% of the original energy rather than over 87%. At those rates, the extra few percent really matters. So why use an ICE? The obvious answer is that this allows them to employ a combination gasoline/hydrogen car without requiring separate systems. The same tank and the same engine can operate on both kinds of fuels. Still, this is considered insane even by pro-hydrogen auto makers:

BMW's competitors are somewhat puzzled by the company's decision to adapt combustion engines -- known for their high fuel consumption -- so that they will run on a fuel as sensitive and problematic as liquid hydrogen. "We think it's nonsense," says Frank Seyfried, research director for hydrogen-based propulsion at Volkswagen.

With the exception of BMW, every car company out there is betting on a different technology: fuel cells, which transform hydrogen into electricity via a chemical process.

Well, every company except for Ford. At any rate, I mention this to make a point: Just because a car company decides to spend gobs of money on something that doesn't mean they had a good reason. A common refrain from hydrogen advocates is that auto makers wouldn't be investing in hydrogen if it they weren't serious about it. That makes sense unless you consider the possibility that hydrogen cars are intended only for show, not for eventually replacing gasoline.

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Why Hydrogen is Stupid.