Getting a Charge Out of a Tesla

PHOTO CREDIT: DAN FINK / SUNPLUGGERS.COM
Tesla's Roadster shows that electric-car technology is on the fast track.

By Dan Fink
On and Off the Grid

Published March 9, 2010

It jumped off the line like a Learjet, pressing me hard back into the sculptured seat. Less than four seconds later, we were doing 60 mph. But instead of the loud roar of a Ferrari Spider or Porsche Carrera accelerating just as fast, the only sounds audible in the Tesla Roadster cockpit were a gentle high-pitched whine from the electric motor and the wind trying to remove my hat. I could even hear birds singing as we ascended switchbacks on a tortuous canyon road west of Boulder, Colo.

I'm fairly sure I heard some snapping noises too, as the heads of drivers, bicyclists, hikers and deer spun at the passing of this mean-looking, nearly silent machine.

Not bad for a plug-in electric sports car that's twice as efficient as a Toyota Prius Hybrid, has a 250-mile range and charges from empty to full in 3.5 hours from a home 240-volt wall outlet.

Boulder has long been known as a center of “green” philosophy — and also as a very expensive place to live. Tesla Motors is betting that their new dealership here will be a success, as the $109,000 base price means this is not an electric car for the masses.

PHOTO CREDIT: DAN FINK /
SUNPLUGGERS.COM
Tesla is working on a
number of models for the
future, some priced
at $50,000.

That's not really the point, Tesla Motors sales advisor Nigel Zeid explained during our test drive. “Tesla Motors is not an elitist car company who will only talk to you if you earn seven figures,” Mr. Zeid said. “This is our trickle-down technology. People who are fortunate enough to buy this car are pioneers, and have allowed the company to continue so that we can start building much more affordable cars for the future.”

In the works are the $50,000 Tesla S series Sedan with delivery scheduled for 2012, a crossover SUV and a commercial delivery van for fleets. The S series is already getting attention and pre-orders, Tesla regional manager Tony Longhurst told me. “If  we could get 200 of them a month right now, we'd probably sell 200 a month,” Mr. Longhurst said.

Range Anxiety

So-called “range anxiety” is a big concern for anyone considering purchasing an electric car, and in Boulder it's no different. The most common question for their sales staff is “How far does it go on a single charge?” Mr. Longhurst said. “The answer is up to 250 miles, but of course range depends on wind, hills, and how hard you drive the car.”

“New Tesla owners tend to drive quite hard at first,” Mr. Zeid added later. “But even if you drive 70 miles to your office and have only a 110 VAC outlet available there for charging, you are still putting 5 to 10 miles of range per hour of charging back into the car while you work. When you get home, just remember to plug the car in to your fast charger and it will be full in less than 3.5 hours.

"You never forget to plug in your cell phone when you get home from work, do you?” Mr. Zeid said.

PHOTO CREDIT: SUNPLUGGERS.COM
Future community charging stations will
use 440 VAC circuits to charge the car in
15 to 45 minutes.

Future community charging stations like those being planned in Boulder and other communities (and already in operation in California) will use 440 VAC circuits to charge the car in 15 to 45 minutes. Swipe your credit card, plug in your car, and go have lunch. Everything will be full when you return.

Because the Roadster uses regenerative braking from the motor to slow itself, city drivers in stop-and-go traffic and mountain drivers climbing hills can recover some of the energy they've lost. The mechanical brakes need only be applied rarely in normal driving. Let your foot off the accelerator (it's not called a “gas” pedal anymore) and the car uses its momentum to charge the battery bank and slow you down.

“We have a gentleman who lives up in the mountains west of here,” Mr. Longhurst said, “and every time he comes into Boulder he arrives with more range than he left with 30 miles ago.”

Those of us who have leaned green for a couple decades find a 250-mile range astonishing. Back in the day, converted electric Volkswagens and small pickup trucks could achieve only 30 to 50 miles on a charge, and they face nearly the same limitations now. Even a 50-mile range wouldn't get me to town and back without a recharge.

When we pulled the car over for a photo shoot and shut it off, I noticed a faint humming noise coming from the rear. It was the battery bank, circulating coolant. The Tesla stores energy in lithium-ion batteries, just like those in your laptop computer. And I mean just like them — these are industry-standard “18650 form factor cells” like those found in most laptops. Except that there are 6,831 of them encased behind you in a protective cradle.

Li-ion batteries have been a huge innovation in battery technology, but they are well-known for being fragile and susceptible to the slightest abuse in charging or discharging. Burning and exploding Li-ion cells onboard airliners forced new FAA regulations and recalls from Dell, Apple, IBM and others. Two-year-old laptops often have only minutes of run time left at full charge, and replacement battery packs can cost more than the computer is worth, a large source of irritation to business travelers.

How does Tesla Motors get around this problem? They claim a battery-bank life of 100,000 miles or seven years.

The World's Most Pampered Battery Bank

Few batteries die a natural death. Most are murdered.

The ideal conditions for longest Li-ion cell life are at cold temperatures with a low state of charge. Your poor laptop battery is kept always full by its wall charger, and is constantly cooked by the high temperatures of your microprocessor. These are the worst possible conditions for Li-ion battery life.

PHOTO CREDIT: DAN FINK / SUNPLUGGERS.COM
The Tesla's 6,831 lithium-ion batteries
are encased in a protective cradle.

In Tesla vehicles, each string of cells in the battery bank is monitored by the car itself, 24/7. Coolant circulates when needed by an electric pump. If any individual part of the battery bank begins to show a problem, microprocessors isolate it and it can be replaced without touching the remainder. The car tells you to please schedule a service call.

“If one or two or a dozen cells go bad, it doesn't stop the car from working,” Mr. Zeid said. “You won't even a notice a difference in performance.”

The car's intelligence also tries hard to maximize battery life with how fast and far it allows you to drive, but allows you to override its control if needed. If some smug fellow in a Porsche pulls up next to you at a stoplight, you can switch to “performance” mode and smoke him off the line.

On the other hand, if you are 60 miles from home with only 30 miles left in the battery, the car will automatically conserve energy to extend your range by more than double.

As for the safety considerations of Li-ion cells, both in actual driving and in shipment, Tesla relies on multiple layers of redundancy. Each cell has two different over-current protection fuses built into it, and each string of cells has its own microprocessor for control. All parts of the battery bank communicate with each other and with the car itself, and more internal battery-bank sensors detect inertial changes from a collision, position changes from a roll-over accident, smoke, humidity and moisture, instantly disconnecting everything.

101 Uses for a Dead Battery Bank

 Tesla Motors makes no secret of the fact that all batteries eventually die. Their claimed seven-year lifespan is actually quite good compared with most battery banks used in off-grid power systems. But what happens when the battery bank has lost its oomph?

According to Tesla CEO Elon Musk, the current replacement cost is $36,000. The company is betting that Li-ion cell prices will drop over the next few years, too — so worried customers can pay $12,000 right now for a battery pack to be installed in 2016 when their current one starts to wear out.

All involved would certainly hate to see such a battery engineering marvel go to a landfill, even though it legally could be disposed of there since there are no toxic substances involved. Fortunately, the entire battery pack is recyclable.

Tesla has set up an exchange program where owners get credit for the materials salvaged from their old battery bank, which will then be shredded. Plastic, metal, and copper-cobalt are recovered.

PHOTO CREDIT: SUNPLUGGERS.COM
The Tesla has been drawing plenty of
attention at auto shows and on the road.

What excited me most, though, were other prospects for these used batteries that Tesla has proposed.

They figure that consumers will consider the batteries spent when they have lost about 30 percent of their capacity. “The remaining 70 percent is still perfectly usable,” said Mr. Zeid, “and in the future will be providing back-up power for homes.” He went on to point out that home back-up batteries see far more peaceful conditions then those in vehicles, and that used Tesla batteries could see a long second service life. With Boulder's new smart grid initiative, that could be a perfect fit.

As for me — 11 miles from the nearest power line and relying entirely on solar and wind for my electricity — all these ideas are starting to sound really tempting.

A Tesla Roadster is not in my future; it doesn't even have enough ground clearance to make it up my driveway in the mountains. But I could buy the Tesla crossover SUV when it comes out, then add some extra photovoltaic modules and a larger wind turbine to my system to charge it. When the battery pack fails, move it to my off-grid home and buy a new pack. The Tesla battery bank stores 53 kilowatt-hours. My current one, which is much larger and twice as heavy, stores only 19 kwh.

This is all starting to make sense — and when electric cars start to make sense way up here off the grid, I start to listen.

Dan Fink, a renewable-energy author, lecturer and consultant, has lived off the grid, 11 miles from the nearest power line, since 1991. He is co-author of the book "Homebrew Wind Power," and his work appears frequently in renewable-energy magazines such as Home Power and Back Home. You can email him at dan.fink@sunpluggers.com.