July 19, 2010

You can't "jump" an EV

The Nissan Leaf is getting plenty of positive press these days. But when it comes to the pragmatic demands of the American market, the technology of the Chevrolet Volt trumps that of pure electrics.

The Volt miniaturizes the diesel-electric system that's been powering locomotives for more than half a century (minus the batteries). The internal combustion engine provides zero torque at zero RPM (hence the clutch), while an electric motor provides infinite torque at zero RPM.

Very useful when accelerating massively heavy objects from a dead stop.

But this is why the inherent advantages of hybrid systems mostly disappear at cruising speed. However, I suspect the costs associated with the Volt's steeper engineering curve (including battery R&D) will make the Nissan Leaf the more affordable pure "green" buy in the near future.

Even with the Leaf, though, that green will cost you a whole lot of green. Lexus prices for a Corolla ride.

The all-electric is a simpler engineering challenge. But it has a big problem. You're not going to drive one across Nebraska. Or, in my case, barely to the airport and back. If all-electric vehicles become as popular as the advocates hope, what happens when they run out of juice?

I've drained my ordinary lead-acid car battery twice by leaving things on. Two batteries have failed (one exploded). The last one had enough life left that I walked to the auto shop and borrowed a portable jump starter like this cute unit. It had just enough oomph to start my car.

I've run the tank dry once. I walked across the street to a gas station and bought a gallon of gas. I had a motorcycle in college. It had a reserve tank you could access by flipping a valve under the main tank. Of course, once you've used it, you can't not know it's there.

But the energy density of gasoline is so high that a motorcycle can go fifty miles just on the reserve. This is why (a la Seinfeld) when your car's gas gauge reads "empty," you've got a big safety margin.

An electrical metering system, on the other hand, reports exactly how much power is left. One "fail-safe" technology is a low-current "limp home" mode that kicks in when the battery is drained. But how many people want to spend a couple of hours covering the last twenty miles?

And even if you have a fast-charge battery, the laws of thermodynamics say that tow trucks will have to haul around huge, industrial-sized generators (diesel-powered). A 49 KW fast charger for the Leaf will set you back $16,200. Except the typical house can handle only half that load.

By "fast charge," we're talking 15-30 minutes, instead of 8 hours plugged into your home outlet. In the brave new EV world, you'll need an insurance policy just for the "roadside assistance." The Volt has a gas-powered battery charger under the hood--hence the high cost but great range.

Alas, the main obstacle here--the laws of physics--cannot be overcome by throwing lots of money at it. Recall that before the Manhattan and Apollo projects began, the underlying scientific challenges--the liquid fuel engine (1926) and nuclear fission (1941)--had already been solved.

Back during the waning days of Apollo (yes, I was alive back then), we were assured that fusion was just a few billion dollars away from becoming a reality. Forty years on, the basic scientific problem has still not been surmounted, let alone all the engineering hurdles if it was.

Lithium-ion batteries have an energy density of .72 MJ/kg. A conventional lead acid battery has an energy density of .14 MJ/kg. So production EV batteries are only five time more efficient than a technology invented in 1859. Gasoline has 62 times the energy density of a lithium-ion battery.

A lithium-ion battery pack that would give an EV the same range as the average gas-powered sedan would weight twice as much as the car itself.

So it makes a whole lot more sense to just use up all the natural gas and oil first, then synthesize butanol (less corrosive than ethanol and can be piped). Or diesel from algae, if that ever works. Butanol has an energy density of 37 MJ/kg, only slightly less than gasoline and LNG.

But if you really want to go electric (and carbon dioxide upsets you), first build lots of nuclear power plants. One pound of enriched uranium-235 has the same energy density as a million gallons of gasoline. The U.S. has tons of that too.

While we're at it, Japan produces energy efficient cars not because of CAFE standards, but because gasoline in Japan costs $5/gallon, and gas guzzlers are taxed within an inch of their lives. And yet the streets of Japan are not crowded with EVs. Electricity has high costs too.

The low power densities of solar and wind in particular will require huge electrical grids, which depend on the mining and smelting of millions of tons of aluminum, copper, and iron ore, not to mention importing the lithium and rare earths for the generators, PV panels and batteries.

For the uninitiated, this is what a copper mine looks like:

A more realistic solution is the "greenest" and is the fastest growing in China and Japan: electric bikes. But their utility is due to high population densities, which are the product of high relative energy and land costs. And they are an order of magnitude more dangerous.

I'm not sure where you'd put the car seat. Or the groceries. Or how you drive one when there's two feet of snow on the ground and it's 20 below outside. (Or for that matter, how far a Leaf battery will last stuck in a Los Angeles traffic jam with the air conditioner on full.)

Ironically, strict CAFE standards have the opposite effect: they lower the unit-cost of gasoline and encourage sprawl, just as houses get bigger when insulation and HVAC systems improve. We'd rather spend energy savings on making our lives more comfortable, not on saving the planet.

That's no less true of two billion Indians and Chinese. If you want to "save" the planet, you'll have to get a handle on human nature first.

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# posted by Anonymous Dan

The pragmatist in me says the answer is to eliminate the battery.

The essence of a hybrid drive system is the continual and optimal transformation of electrical, chemical and kinetic energy. The battery allows excess energy to be stored and released when needed in the future. How distant is that future? What is the extent of electrical energy time-shifting in an EV?

The Li-ion battery in my camera holds a charge for months. Is this duration of energy storage needed in a hybrid propulsion system? No. So what half-life of energy storage is acceptable for an EV and how much would changing this design requirement reduce the cost of the vehicle?

Why are hybrid vehicle engineers stuck on the the Li-ion battery when it seems to be ill suited for its key function?
7/20/2010 5:45 AM

# posted by Anonymous Anonymous
i think the use of electric scooter or battery electric vehicle is usegull fore all of us
6/09/2016 4:00 AM

# posted by Anonymous Anonymous
6/09/2016 4:02 AM