Results matching “Tesla Roadster Battery Capacity”

For owners who may be new or unfamiliar with the Tesla Roadster, I'll run through the basic information needed to preserve this rare and special vehicle.

The most obvious concern is properly maintaining the battery pack. If the Roadster is left unattended and without power for weeks or months, the battery back will slowly discharge until the pack is fully depleted. If this happens, the battery pack may be ruined. Even if plugged in, if power is interrupted by a popped breaker, extended outage, service disconnection, etc., permanent damage to the battery pack can occur.

Also of concern is temperature. The Roadster should not be left unplugged in extreme temperatures. If the battery pack gets hot, it should be plugged in so it can cool. Consult the owners manual for more information.

Charging

Level 1 In the United States and Canada, the Roadster can be charged at 120V with a simple cord sold as the MC-120. It just connects the car to power with no EVSE logic and the car assumes a 15A circuit suitable for charging at 12A. At this power level, the car can't run the full cooling system and in fact uses a lot of the power just to run the coolant pump. This means a slow rate of charge, and in fact in hot weather, may use all of the power just trying to cool the battery pack. In comfortable weather, not too hot and not too cold, and no rush to get charged, this can be an effective way to charge. Some owners used Level 1 exclusively. Since the coolant pump tends to run continuously, even after charging is complete, there may be a corresponding reducing in the lifetime of the coolant pump.

Level 2 charging means connecting to 240V single-phase power using an EVSE that communicates the maximum current draw allowed for the circuit. It uses the same communication protocol as standard J-1772 charging stations. Having more power means the battery pack can be better thermally managed, which can make quite a bit of noise when the fans, compressor and pumps are all going full tilt. The maximum charge rate of the Roadster is 240V/70A. Unless we were in a hurry on a road trip, we generally charged at 240V/32A which yields good energy efficiency and may be nicer to the battery.

The Roadster can charge from a standard J-1772 station with an appropriate adapter. Tesla sold one for a while and there's an aftermarket adapter.

Charge Modes

The Roadster has four charge modes, used for different purposes.

Standard Mode limits charging to the middle 80% of the battery pack, not letting the charge level get too high and warning the driver, and even shutting the car down, before getting critically low. This is the mode used for daily charging of a Roadster that's driven locally with some regularity.

Range Mode opens up the full charging range, allowing a higher state of charge and enables driving down to a lower start of charge. Range mode also limits power from the pack, and thus reducing maximum acceleration in the name of extending range. Occasional range mode charging didn't seem to have a negative effect on our battery pack, but charging frequently to the top of range mode may accelerate the loss of battery capacity. When we owned a Roadster, we'd do a full range mode charge at the start of long road trip, then switch over to standard mode for driving.

Performance Mode uses the full charging range, allows the battery to get warmer while charging, and allows maximum power (full acceleration). This is appropriate for driving on a track, but probably accelerates loss of battery pack capacity if used often.

Storage Mode displays the state of charge like Standard Mode, but will let the state of charge drop to around 30% then will maintain that level of charge. This is the best mode to use when the Roadster won't be driven for weeks or months. The car must be plugged in to maintain the health of the battery pack. The disadvantage of Storage Mode is that if the power supply is interrupted, it will start discharging from around 30%, so it will get into trouble sooner than if left in Standard mode. That's probably more of a concern if it's in long term storage and ignored vs. being kept for the winter in your garage where you'll notice of the power goes out or the breaker gets tripped.

An example charge screen:

The drawing below shows how to interpret the state of charge in the two main charge modes. Range values are for the original 53 kWh battery pack when new.

Vehicle Log

The Roaster maintains a detailed internal log which can be downloaded via the USB port in the console. Although the format of the logs isn't documented by Tesla, various owners have been able to decode and extra a great deal of data. The log file has two sections: a long term section that has basic info and a more detailed section of recent driving and charging. See the page on the VMSParser I created for more information.

Remote Monitoring

The Roadster did not have support for remote monitoring, not at all for the 2008 (v1.5) Roadster and nothing driver-accessbile for the 2009 and later (v2) Roadster.

There is an aftermarket system availble, the Open Vehicle Monitoring System or OVMS. OVMS allows for remote monitoring of charging, GPS tracking, custom charge settings, and viewing battery metrics. In addition to allowing manual remote monitoring, it can also send low-battery alerts and unexpected motion alerts if the car moves not under its own power.

More Resources

There are a number of other entries on the blog detailing our adventures with the Roadster, plus another collection of longer Roadster articles of practical and historical interest.

The Tesla Motors Club forum is the best community resource around, although its focus has natually shifted to the newer Tesla vehicles.

Charging an electric vehicle is pretty easy: just like my cell phone, I plug it in when I get home and it's fully charged in the morning. It doesn't matter how long it takes because I'm not waiting for it to finish; the car just charges up and waits for me.

Tesla Motors was the first automaker to sell a production electric vehicle based on lithium ion batteries, the Tesla Roadster. Current Roadster owners as well as other prospective electric vehicle owners are interested to know how these batteries will hold up over time and miles.

It's still pretty early in the game. Tesla Motors tells us that we should expect to have our battery packs holding 70% of their original capacity after 5 years or 100,000 miles. The oldest Roadsters are a bit over three years old and some vehicles are getting up into the 30,000+ mile range.

How are the battery packs holding up so far? I've collected data from 20 owners in the Pacific Northwest to get an approximate idea of our batteries are performing.

Before we dive into the results, I should explain a bit about how battery capacity is instrumented on the Roadster. The Roadster has two primary charging modes. Standard mode charges up to about 90% of the pack's capacity and holds the bottom 10% of the capacity in reserve. Range mode fully charges the battery pack and shows the full range available, including the bottom 10%. The range is shown in two ways, "Ideal Range" and "Estimated Range." Estimated range states the range based on recent driving history and so can't be compared across vehicles. Ideal range shows how many miles you can drive in the current mode if driving with the same mixed city/highway average energy use that gave the Roadster its EPA -rated 245 mile single charge range. The corresponds, for example, to driving 55 to 60 mph on level freeway in moderate weather.

First, let's see how miles driven affects battery capacity.

The red squares at the top of the graph show the range mode capacity expressed in ideal range miles (aka ideal miles) versus miles driven on each battery pack. The blue diamonds show the standard mode range. The straight lines show the tread for each set of readings. I interpret this graph to show that for this set of vehicles, individual variation between cars is larger than the pack degradation over approximately 30,000 miles. For range mode, the variation between cars is as much as 15 ideal miles between cars with comparable mileage, while the linear trend shows a drop of only 5 ideal miles across 30,000 miles of driving. For standard mode, the variation between cars of comparable mileage is under 10 ideal miles while the trend line shows a drop of perhaps 6 ideal miles.

Lithium ion batteries lose capacity over time even if you don't use them. The graph shows the same vehicles over time instead of miles.

Again, we see the same apparent patterns: variation between vehicles is larger than the average range lost over three years and variation in range mode is larger than the variation standard mode.

While this is enough data to see some patterns emerge, it's a small fraction (about 1%) of the total Roadsters on the road. I'd like to collect more data to confirm these trends and also separate the effects of time and miles. Most of the Roadsters in this set are in the relatively mild coastal climate of Oregon, Washington and British Columbia. It would be interesting to analyze data from Roadsters in more extreme climates.

How do the Tesla Roadster and Nissan LEAF compare in energy use?

Tesla Roadster owners have been driving electric for a couple of years now and have built up knowledge about how much energy is required for many different routes and driving scenarios. New Nissan LEAF owners could perhaps benefit from what Roadster owners have learned, especially in the near term while charging stations are few and far between.

On August 4, 2011, we did a test to answer a couple of questions:

How does energy use in a Nissan LEAF compare to a Tesla Roadster?

Does knowing how much energy a Roadster uses for a certain drive help a LEAF owner plan the charge needed for a long drive?

The Plan

To take a first stab at figuring things out, Cathy and I joined up with her parents, Jim and Barbara Joyce, to drive a Nissan LEAF and a Tesla Roadster on an interstate freeway up a mountain pass. We wanted to compare just the two cars and eliminate as many other variables as possible. We drove up together so we had identical road and weather conditions, put the cars on cruise control to minimize driver differences, and restricted ourselves to using the fan but not air conditioning. From Roadster data collected on previous drives and also a recent LEAF drive up the same pass, we were pretty confident it could be done from the Joyces' home even cruising at 70 mph. We were right.

The Route

We started at the Joyce residence near where Washington State Highway 18 meets Interstate 90 at Exit 25. Their LEAF started with a full charge. We drove to I-90, recorded trip and energy data at the stop light at the base of the on-ramp, accelerated up to 70 mph, then locked on cruise control. We exited I-90 at Exit 52 and recorded trip and energy data at the bottom of the off-ramp. We puttered around the summit for a bit, got some lunch, then reversed the route, again recording data at the bottom of the on-ramp getting back onto I-90 and again after exiting the freeway back at exit 25.

The Results

The graphs below show energy use for both vehicles up the pass from exit 25 to 52, a distance of 27 miles with a 2,000 foot elevation gain, then the descent back down from exit 52 to exit 25.
The graph shows that the LEAF used about 6% more energy than the Roadster on the way up and about 13% more energy on the way down. Both vehicles used about twice as much energy on the way up as the way down, although that ratio depends on the slope and speed. For a sufficiently steep road and slow descent, an electric vehicle can actually gain net energy driving downhill. At 70 mph, we did not see a lot of energy production, just low energy driving. At slower speeds, more energy would have been produced on the steep sections of the descent.

The LEAF averaged 2.7 miles per kWh (376 Wh/mi) on the way up and 4.8 mi/kWh (233 Wh/mi) on the way down, for an average of 3.3 mi/kWh (305 Wh/mi).

The Roadster averaged 2.8 miles per kWh (355 Wh/mi) on the way up and 5.5 mi/kWh (206 Wh/mi) on the way down, for an average of 3.6 mi/kWh (271 Wh/mi).

How Much Charge is Needed to Drive a LEAF Up to Snoqualmie Pass?

The LEAF doesn't give an indication of the state of charge to any useful precision, so we could only measure energy use from the trip miles and miles per kWh supplied by the LEAF. In terms of how much charge we used, the LEAF started with a full charge and ended back home with one bar showing and 4 miles on the generally worse-than-useless guess-o-meter. This included under 10 miles of driving between the freeway and home. It was a little surprising that the LEAF charge got so low given that the home-to-home energy use was only about 18 kWh, but the reported 24 kWh capacity of the battery is probably measured at a discharge rate that's lower that what's needed to climb the pass at 70 mph. Also, we know the LEAF hides some reserve charge from the driver.

From this data I conclude that starting from a full charge in Snoqualmie or North Bend, a LEAF can easily make it up and down the mountain at the speed limit without climate control. With climate control on, a bit slower speed may be required.

With a DC Quick Charge to 80% at North Bend, it could probably be done by anyone starting in the greater Seattle metro area.

Having Level 2 charging at the summit would be a big help. Even Level 1 would make a difference for someone spending the day skiing at the pass and wanting to get home with little or no charging on the way back.

Driving at lower speeds would use less charge. Really efficient driving, including better use of regenerative braking on the way down, would further decrease the charge needed.

Comparing the Nissan LEAF and Tesla Roadster

The curb weight of the Roadster is about 2,700 lbs, compared to the LEAF at 3,350 lbs. So the LEAF weighs about 25% more than the Roadster. The LEAF has a more aerodynamic shape, but has a much larger frontal cross-sectional area, so I would expect the LEAF to also have more aerodynamic drag. At freeway speeds, one would expect the aerodynamic drag to be a bigger factor in energy use, but doing a significant climb increases the importance of vehicle weight.

Because of how these two issues interact under different conditions, these numbers tell the story only for this specific drive on this route at this speed. Other drives are likely to give different results, so more tests are needed to get the full picture. It would also be interesting to do the same drive with multiple LEAFs and Roadsters to see how much variation there is between vehicles of the same model.

Data Method and Repeatability

We did everything we could both to minimize the difference between the two side-by-side drives and also standardize the drive so it could be repeated later under either similar or different conditions.

It was warm enough that we had to run the car fans to stay comfortable, but we were able to avoid use of the air conditioning.

Trading a gas pump for a plug is a wonderful thing. It's far more convenient, takes less of your time, and saves you from breathing toxic fumes and smelling like gas for hours after fueling. Charging is a different experience than pumping gas and understanding the subtleties takes time. I've been driving electric for over two years and I'm still learning. Potential EV owners might want to get a head start on the learning curve, and maybe save a bunch of money as a result.

Mostly, I'll relate how charging works for a Nissan Leaf, a four-door, five-passenger hatchback with a range of about 100 miles, but I'll also mention other plug-in vehicles. The Leaf is intended for typical daily driving, which for 78% of drivers in the US means 40 miles or less per day. Occasional longer trips are possible and understanding charging will help you evaluate whether an EV will suit your driving needs.

Level 1 Charging

Level 1 Charging - Standard House Outlet

Level 1 charging is the technical jargon for plugging your car into an ordinary household outlet. For a Leaf, this means about 4.5 miles of range per hour of charging, or about 22 hours for a full charge. Wow, does that sound terrible! But there's a problem with thinking this way: you'll rarely need to do a full charge from flat empty to full. If you drive 40 miles per day and charge overnight, you'll be back to full in 9 hours. When you're sleeping, it doesn't matter if it takes one hour or 9 hours to charge.

But what if you have to drive a lot one day, say 80 miles? Sure, it would take 18 hours to get a full charge, but with a 9-hour overnight charge, you'll be ready for your normal commute the next day. If you drive less than 40 miles per day or charge for more than 9 hours, you'll work back up to a full charge over the next few days.

If you need to drive 80 miles on consecutive days, you'll need an alternative. Maybe you'll drive your other car, that gas-burner you keep around for long trips, or if there's public EV charging in your area, you can charge away from home while you're parked to do your shopping or other errands.

Level 1 charging at work could also be a supplement for people driving over 40 miles per day, or even a substitute for those who can't charge at home (because they don't have a garage or fixed parking place, for example).

Since it's easy to get 40 miles of range charging overnight from 120V, Level 1 is perfectly suited for overnight charging of the Chevy Volt, a plug-in hybrid with a 40-mile all-electric range.

Although Level 1 charging is generally too slow for a road trip, it can be helpful as destination charging. Cathy and I drove 90 miles to San Juan Island, charged for a few days in a friend's garage when not cruising around the island, and left with a full charge. That was great, but I wouldn't want to have to wait for Level 1 charging in the middle of a travel segment.

Beyond range issues, Level 1 may not be suitable for primary charging in all cases. In extreme climates, more power may be required to maintain proper battery temperatures. In these cases, Level 2 charging may be more appropriate (see below).

DC Fast Charging

Blink DC Fast Charge Station photo by ECOtality

At the other end of the spectrum is DC Fast Charging, the fastest type of charging currently available. It provides up to 40 miles of range for every 10 minutes of charging. These stations are expensive (up to $100,000) and require more power than your house, so you'll never have one of these in your garage.

They are going to start appearing as public charging stations in the next year, beginning in the Leaf target areas. If there's one conveniently located near where you drive, you can get back up to 80% of a full charge while getting lunch or drinking a latte. Charging this fast makes it far more practical to drive beyond an EV's single-charge range in one day. It's still not going to make a one-day 800-mile drive practical, but a 200-mile drive with a couple of charging breaks can be quite doable.

Level 2 Charging

ChargePoint/Coulomb Level 2 Charging Station

Between the cheap Level 1 and expensive DC Fast Charging stations sits Level 2 charging. Level 2 supplies 240V, like what an electric dryer or oven uses. It goes through a box and a cord that improves safety by waiting to send power to the plug until it's plugged into an EV. Level 2 allows for a wide range of charging speeds, all the way up to 19.2 kilowatts (kW), or about 70 miles of range per hour of charging.

However, the charging stations being put in with federal grant money don't support the full range of Level 2 charging and max out at 6.6 kW or around 26 miles of range per hour of charging.

Both Level 1 and Level 2 charging stations simply deliver household electricity to the car. Electronics on board the car transform the wall power into the proper form to charge the battery. This bit of electronics built into the car also has a maximum power rating. The first model-year Leafs can only use 3.3 kW, about 12 miles of range per hour, or about 8 hours for a full charge from empty. The Chevy Volt's on-board charger is also limited to 3.3 kW, although its smaller battery pack gets full sooner.

Nissan recommends that you install a Level 2 charging station at home. That's a reasonable thing to do if you don't mind spending about $2,000, just consider it part of the cost of the car. Early buyers in the Leaf target markets may be able to get into The EV Project and get a free Level 2 charging station plus an allowance toward the install cost. Failing that, there's a 30% federal tax credit (up to $1,000) for installing EV charging, which can make it less expensive. Still, if you are planning to use your EV for a daily commute of 40 miles or less per day, you should at least consider using Level 1 charging at home. You can always add a Level 2 charging station later if you decide you need it.

There will soon be 20,000 public Level 2 charging stations (limited to 6.6 kW) installed mainly in the Leaf target areas. Even if you only have Level 1 charging in your garage, if you're in the early rollout areas, you should have access to convenient Level 2 charging available while your car is parked and you're doing something else. These charging stations will make it possible to drive 60 miles to a baseball game and pick up about 50 miles of range in 4 hours while you're having fun, thus easily driving over the single-charge range while always keeping a healthy reserve.

Charge Time and Battery Capacity

It's misleading that charging times are generally quoted as time for a full charge. While it does take about 22 hours (Level 1) or 8 hours (Level 2) to charge a Leaf from empty to full, you're not likely to do that often because  you will rarely arrive home with a fully depleted battery. It doesn't matter if you're driving a 40-mile Volt, a 100-mile Leaf or a 240-mile Tesla Roadster, if your commute is 40 miles, you'll only need about 9 hours (Level 1) or 3 hours (3.3 kW Level 2) to charge.

When we bought our Tesla Roadster, we got the high-power 16.8 kW Level 2 charging station, which can charge the car in 3.5 hours. After driving the car for a few months, I realized it's all but pointless to have such a big charging station in our garage. It's rare that I drive over 40 miles in a day. The 16.8 kW charging station can restore 40 miles in under 40 minutes. I want that charging speed when I'm making a long trip, not when I'm sleeping at home. In fact, I manually drop the power I pull from the charging station to about 7.5 kW because it's a little nicer to our electrical panel and the grid, and my typical overnight charge is still under 2 hours. Ignoring the fact that Tesla is still using the now-incompatible proprietary charging plug they picked before there was a chosen standard, most people buying a Tesla Roadster today would be well-served to buy a 6.6 kW charging station for home.

3 Roadsters Sharing the Charging Station at Burgerville

Level 2 Charging, Road Trips, and Charging Speed

Already, Ford has announced that the upcoming electric Ford Focus will support charging at 6.6 kW, and is making fun of the Leaf's 3.3 kW Level 2 charging limit. By the time Ford actually starts delivering the electric Focus, Nissan may have already upgraded the Leaf to 6.6 kW charging. I don't think it will be long before mainstream EVs are capable of even faster charging. The Tesla Roadster can charge at 16.8 kW, which combined with a larger battery pack makes 400-mile drives possible even without DC Fast Charging. Given that Level 2 charging costs 1/10 of what a DC Fast Charger does, I can imagine a lot of driving being supported by full Level 2 charging stations in areas that can't justify the investment in DC Fast Charging.

Personally, I'm disappointed we're spending so much money installing these 6.6 kW public charging stations rather than full-speed Level 2 chargers when most of the expense is usually just running the wires and buying the fancy box. A typical commercial Level 2 install runs around $10,000 for a charging station that's connected to a network and capable of billing the user. Cranking those charging stations up to the 19.2 kW limit would add a small incremental cost, perhaps 10%, and would allow for much faster charging. If you're a business owner installing a charging station and have to dig a trench and/or run conduit, even if it's just a for 6.6 kW unit, I strongly recommend planning for running 100A wire later without having to retrench or replace conduit so that upgrading to a 19.2 kW charging station will be much less expensive.

If you are interested in driving an electric vehicle, I'd like to tell you how to ensure that you'll have a great experience, or at least make sure you don't have a disappointing experience.

Here's the secret formula for EV success: make sure the range of the vehicle suits the driving you plan to do with it. I know that sounds pretty obvious and easy, but there are two big barriers to success: bad reporting in the media and obfuscation by the automakers. There's also a bit of complexity: just like gas mileage, you can't express EV range with a single number. I'll get that all straightened out from the perspective of someone who has been driving all electric for almost two years.

In addition to the general facts of driving electric, we recently got some more specific range numbers for the upcoming Nissan Leaf which I'd like to put into perspective for potential buyers.

Reporting the Obvious and Irrelevant

If you follow EV coverage in the press, you'll find a steady stream of articles from reporters who think they've discovered the flaw that will deflate all of the hype about EVs. Their basic premise is that EVs won't work because they take too long to charge and there's nowhere to charge them. These articles are either totally made up, or based on the bad experience of a single EV driver and don't represent the real experience of the majority of EV drivers who purchased a vehicle appropriate for their needs. My purpose here is to make sure you don't become the excuse for some lazy reporter to write yet another of these uninsightful articles.

Would a newspaper publish an article about a Ford Focus owner who was disappointed that he couldn't fit his wife and seven kids in the car? How about a Honda Civic owner who's mad her car isn't suited for towing an RV? A Hummer owner who's mad about how much it costs to drive a mile? Of course not, these would be laughably obvious mistakes made by the owner in choosing a car.

For the consumer properly informed on the benefits and limits of electric vehicles, it's equally obvious that buying an EV with a 75-mile range to do a daily 74-commute with no charging infrastructure isn't going to yield a happy driver. That's obvious and boring.

The real story is that there is no problem with range or lack of charging infrastructure if you can just charge at home to meet your driving needs, instead it's a real convenience not to have to fuel your car away from home. So let's see if you qualify...

The Rule

To be a happy EV owner today, you want to buy a car that has enough single-charge range to handle all of your daily driving with a reasonable buffer for typical errands without needing to charge anywhere other than your charger. (Your charger is probably installed at your home but might also be at your work location.)

The good news is that for most drivers, the required range is surprisingly low. A 2003 US Department of Transportation survey (PDF) found that 78% of Americans drive less than 40 miles a day. If you're in the 78%, and don't often have big exceptions to that daily commute distance, then an EV that gets at least 70 miles of range in your driving conditions will most likely make you one happy camper. (But keep reading to learn how to evaluate EV range.)

Starting this fall, we'll start to see a lot of chargers getting installed in a few metro areas in the US and other countries. As this happens, and EV ownership goes up, more and more charging will become available and convenient. As that happens, charging away from your home charger will become more dependable and the usable range of EVs will expand as a result. For example, if you can charge at home and at work, then the usable range of an EV is doubled because you only need to travel one way on a single charge (with a reasonable buffer).

Since there's going to be limited availability of affordable, practical, freeway-capable EVs in the near future (as in zero today, and a few thousand Nissan Leafs starting to trickle out starting in December of this year, then more from other automakers to follow), it's OK if the first few models of EVs don't work for you, they will work for millions of potential buyers. Wait for an EV that will be right for your driving needs.

The Win

After you've driven electric for a month, spending just a few seconds to plug in each night to start every day with a full charge, without ever having to stop at a gas station, you'll wonder how you ever tolerated the hassles of driving a gas burner.

In addition, the experience of driving electric is just better: you get instant acceleration without waiting for the engine to rev up and the transmission to shift, another nuisance of driving gas that you'll only notice when you get used to driving without it.

Bonus: no tailpipe emissions, low-to-zero emissions from electricity generation, and never having to worry about the price at the gas pump.

Evaluating EV Range

Just like gas mileage, EV range can't be expressed as a single number. Even the two EPA city and highway gas mileage numbers you see on vehicle stickers don't tell the whole story. This is such a big issue with gas cars, the caveat "your mileage may vary" has become part of our cultural vernacular.

Let's start by going over how gas mileage works. Those gas mileage numbers on the sticker in the window are determined by driving the car on two standard EPA driving profiles meant to simulate typical driving conditions, which have been recently revised to better represent actual driving conditions by including things like using air conditioning on part of the cycle.

Gas mileage depends on a number of factors, including passenger and cargo weight, HVAC use, start/stop frequency, road incline, rain/snow, and so forth, but the biggest factor is speed. At low speeds, gas mileage suffers because there's an overhead of running/idling an engine that burns fuel whether you're moving or not. Stop and go traffic is also bad news, because you invest energy in speeding up only to throw all it all away by converting your car's momentum into heat plus wear and tear on your brake pads. At higher speeds gas mileage suffers because wind resistance goes up rapidly with speed, so much so that it takes more energy per mile in a way that starts increasing dramatically at the low end of freeway speeds. Somewhere in the middle, at a moderate, steady speed, is where you get your maximum gas mileage.

Electric vehicles behave similarly, except they get punished less in stop and go traffic because, like hybrids, they can slow down with regenerative braking wherein the motor is driven by the drivetrain to act as a generator to put charge back into the batteries. This not only improves energy efficiency, but also reduces brake wear.

Given this complexity, how can an automaker tell you how your gas or electric car will perform under your driving conditions? Answer: they can't.

While you can argue that it's even more important to understand energy efficiency (in the form of single-charge range) for an electric vehicle, there's the ugly truth about burning gas that no one likes to talk about: it's no good for predicting long-term fuel costs. With a proliferation of gas stations everywhere, range isn't something you think about for a gas car. What you do think about is your pocketbook. Better mileage means cheaper stops at the gas station. While knowing your gas mileage might tell you what you'll be spending at the pump this month, it doesn't say anything about what you'll be paying next month or next year. Anything from a hurricane, to Wall Street speculators, to a political action by OPEC, to the whim of some oil nation tyrant can cause gas prices to double by barely nudging the precarious balance between world oil supply and demand. Electricity rates are far more stable, especially when it comes from renewable sources that aren't subject to the unpredictable economic forces that rule the world's fossil fuel energy market.

How can a potential buyer figure out if a given EV has the range required to convert from the hassles of driving gas to the joy of driving electric? Read on...

Case Study: the Range of a Tesla Roadster

For most people, buying a $109,000 two-seat sports car is totally out of the question, whether it's a gas-burning Ferrari or an all-electric Tesla Roadster. Being able to go from 0 to 60 mph in under four seconds isn't going to get the kids to school or bring home the groceries from Costco. But, as of this writing, Tesla Motors is the only automaker selling a production, freeway capable electric vehicle in the US. If you dig a little, their web site provides a wealth of information about driving electric that will be of help to any potential EV driver.

The best illustration I have found of the effect of speed on efficiency, and thus range, is this graph from Tesla Motors showing how the Roadster's range varies with speed, while holding other factors constant at favorable values (constant speed, no AC, no driving up a mountain, etc.).



The EPA range number for the Roadster is 244 miles. From the graph, you can see that you get that range driving at about 55 mph. If you have to pick one number to describe range for a Roadster encompassing city and highway driving, this is a pretty good choice, and it's a real number that I've personally verified as much as possible without actually driving the car until it stops. Likewise, the value of about 180 miles for 70 mph matches my real-world experience. Simon Hackett and co-driver Emilis Prelgauskas came close to the graph's 34 mph range number by driving 313 miles on a single charge in Australia last year. Perhaps someone will be patient enough to try out the 17 mph peak on the graph at over 400 miles of range, but that would be a very long drive!

I'd say Tesla did a good job here, picking a reasonable single number for stating range based on some combination of the EPA city and highway cycles. They also provide the graph showing the whole story, at least with respect to speed, although to find it you have to dig down into their blog entries to find the article with the graph and full explanation.

But there's a bit more to the story that requires more digging. The above range numbers are for using the entire battery charge from full to empty, something you really don't want to do on a regular basis because it's not good for the life of the battery pack. For normal daily driving, you don't need 244 miles of range, so Tesla provides a "standard" mode of charging that only uses the middle 80% of the battery pack. This will extend the life of the battery pack and still give you 200 miles of range at 55 mph, or about 160 miles at 70 mph. This is between four and five times what most of the drivers in the US need for their daily commute. For daily driving, the range of the Roadster is ridiculously high. Going on a road trip beyond the single charge range is doable, but it requires patience and planning. This situation will get a lot better as high-speed charging stations start to appear later this year.

The numbers also get worse in really hot weather. Last summer I drove from Portland to Seattle in 100-degree weather, about 180 miles. This trip is easy at 55, in fact even at 65 mph it's no problem. But this trip, with the HVAC system using energy to keep the battery pack cool, it took getting off the freeway and careful route planning to reduce both distance and speed to get home without having to stop for a partial charge.

The upshot: if you live in an extreme climate, with either a lot of sub-zero winter days or 100+ degree summer days, you'll want to add more buffer to your required EV range.

The last big issue is aging of the battery pack: as the battery pack ages, its capacity will decrease gradually over time, then drop more rapidly as the battery pack wears out. Our car is performing the same as it did when we got it one year and 9,000 miles ago. Other Roadster owners have crossed the 20,000 mile mark, and so far I haven't heard of anyone noticing a loss of range. Tesla's battery pack warranty is only 3 years or 36,000 miles, which is in line with other high performance sports cars, but is a bit underwhelming compared to their statements of expected battery life, seven years or 100,000 miles. Nissan says their battery pack should last 10 years, and because the Leaf is a much more mainstream vehicle I expect they will offer a much better battery warranty.

Still, if you're planning to drive your new EV for 5 to 10 years, it's not going to be smart to buy an electric car that's right on the edge of meeting your needs with its full factory-fresh range.

Our Electric Garage

In July of 2008, while we were waiting for Tesla to build the Roadster we reserved in 2006, we were fortunate enough to buy a rare 2002 Toyota RAV4-EV from its original owner in Berkeley, CA. If you've seen Who Killed the Electric Car, then you've know what a great electric driving experience the lucky few drivers had during the brief period where California required all of the automakers to find a way to reduce tailpipe emissions to zero.

When we got the RAV4-EV, we expected it would take care of about half of our driving. We were wrong by a wide margin: it took over 95% of our driving. The only time we burned gas was when we each had to be different places at the same time. Despite our EV enthusiasm, we were range anxiety victims and overestimated how much range our driving really required.

In our experience, the RAV4-EV gets about 100 miles per charge. Even staying out of the top 10% and bottom 20% of the battery pack means we can drive 70 miles per charge under our typical driving conditions, and can handle any driving conditions with enough range we don't generally have to think about it.

When our Roadster finally arrived nearly a year later, we were totally converted to the electric driving experience. Having a second electric car meant we didn't have to choose which of us got to drive the smooth, quiet car.

Our hope is that the Leaf will bring this sort of EV capability into the mainstream in an affordable, practical, safe vehicle.

Nissan Leaf Range Numbers

The first range number we heard for the Nissan Leaf was 100 miles using the EPA's LA4 drive cycle. Darryl Siry gets credit for being the first to point out that the LA4 drive cycle is a poor choice for describing EV range as it's a city driving cycle that's nicer to the range than the combined city/highway drive cycle that is used by Tesla. Siry also wrote a great piece on the issues with range numbers and the need for federal regulations on how they are reported which added perspective to my personal experience and helped inform my writing here.

On June 19th 2010, we got some more range numbers from Nissan via Forbes. To summarize:

• Cruising at 38 mph in 68-degree weather: 138 miles.
• Suburban traffic averaging 24 mph, 77 degrees: 105 miles.
• Urban highway, 55 mph, 95-degrees, A/C on: 70 miles.
• Winter city driving, 14 degrees, averaging 15 mph: 62 miles.
• Stop and go urban traffic averaging 6 mph, 86 degrees, A/C on: 47 miles.

The Forbes article is typical anti-EV fear mongering, the facts presented with pithy commentary but no critical analysis. Have you ever read an article on how your gas mileage drops in stop-and-go urban traffic during the heat of summer or the cold of winter and how much that's going to cost you when you're driving your gas-guzzling SUV? Of course not. But you do hear about how it will affect the range of an EV that isn't even on the roads yet. It's great to get more facts, but try to ignore the hand-wringing hysteria that makes it sound like the federal government is about to repossess all of the gas burners and force everyone to drive a Nissan Leaf.

The fact is, the Leaf doesn't have to meet the needs of every driver in the US. It just has to meet the needs of the few thousand people lucky enough to be able to buy one in the next year. Even that worst-case 47 miles is going to be good enough for millions of drivers now (remember that 78% of US drivers commute less than 40 miles per day) and good enough for even more drivers when there are convenient chargers at workplaces and malls.

Is the Leaf's Range Right for You?

I think the best way to figure out what range an EV needs to have to suit your needs is to monitor your driving. Just write down your odometer when you get home each night. From that, you can figure out how far you actually drive. Be sure to get not only your regular daily commute, but also some examples of exceptional days with extra appointments, shopping, detours, etc. If you have an additional vehicle that would supplement your EV, throw out any long drives that you would choose (in advance) to handle with that vehicle. Then add a buffer for the unexpected, and, if it applies, more buffer for the extreme driving conditions that reduce range.

People who haven't driven an EV will be tempted to always have half of the battery in reserve for surprises, but most experienced EV drivers are very comfortable driving down to 30% or even 20%. (With the Roadster where I get great feedback on the state of charge and know it won't hurt the battery, I have no problem driving down to 10%. With the RAV4-EV, which gives less precise info, we try to stay out of the bottom 20%.)

If you commute 70 or more miles per day in a city that regularly has horrible traffic, freezing cold or sweltering hot days, and isn't planning for charging infrastructure, then don't buy a Leaf to be your only car this year. Wait until the cars and the charging better suit your driving needs. There are more than enough of us to buy up every single Leaf Nissan can make in the next 12 months, so don't become fodder for another annoying article about how EVs are impractical because someone bought one that's not suited to their driving.

If the Leaf's range numbers do suit your driving needs and you want to get an early start driving electric, then sign up, right now. They are going to sell fast. But before you fully commit to a purchase, get the information you need to determine if the Leaf will meet your needs, and get that info directly from Nissan. Don't depend on a conversation with your local auto sales drone.

I'm glad we have learned more about the Leaf's range months before anyone will be committed to buying one. Next up I want to see a graph like Tesla gives for the Roadster range vs. speed under optimal driving conditions. I also want to know if the range numbers given are for using the full battery to its maximum range, or if they include allowance for the reserves at the top and bottom of the charge cycle needed to maximize battery life.

If the Leaf will meet your needs, you won't regret switching away from gas. The benefits of charging convenience and drivability are great motivators to be among the early adopters to buy one of the first mainstream factory electric vehicles.

Gas/Electric Hybrid Vehicles

About ten years ago, the Toyota Prius and Honda Insight entered the US car market and have grown to change the way we think about automobiles, the environment, and energy efficiency. Starting slowly at first, sales of the Prius took off and now they are one of the most popular models sold in the US.

These hybrids are simple to understand: they run on gasoline just like every other car on the road, but they have a battery pack and electric motor that makes them more efficient: they get very good gas mileage.

But it's an odd design to meld two drivetrains into a single vehicle. Why is it more efficient to make a gasoline engine push around an electric motor and battery pack, and also make an electric drive push around the gas engine and fuel tank? It's not clear to me that it is that efficient. If you look at the top fuel efficient 2009 vehicles according to the EPA, you'll see that the top vehicles are hybrids, but their advantage is mostly in city driving. The diesel Jetta is just 10% less efficient than the Prius on the highway. In Europe, there are even more efficient diesel vehicles.

Hybrids work well for city driving because they use regenerative braking to capture some of the energy that is normally just dumped into wearing out your brakes when you slow down for a stop light. Even though only a portion of that wasted energy gets stored in the battery pack, it's enough of an improvement to make the double-drivetrain vehicle more efficient.

Hybrids are able to offset some of the weight of the electric drive by using a smaller gas engine. The electric drive can help push the vehicle up a hill, and get some of that charge back on the down slope.

Gasoline engines are only about 25% to 30% efficient. That is, only about 25% of the energy contained in a gallon of gas makes it to the wheels to propel the car. The rest of that energy is wasted as heat and mechanical inefficiency. A good part of that gets wasted in the transmission because a gas engine only produces high power/torque in a narrow band of RPMs, so multiple gears are required for good acceleration at a wide range of speeds.

An electric drivetrain can be over 80% efficient. There's no heat wasted in exhaust and no reciprocating pistons. Also, an electric motor can deliver high torque and power over a very broad RPM range, so there's no need for a transmission and thus no mechanical losses there. That's how adding the weight of a second drivetrain that is just fed with a fraction of the kinetic energy normally wasted by braking can improve the efficiency of a gas engine in city driving.

Plug-in Hybrid Electric Vehicles

If that little bit of saved energy can be used to create a more efficient vehicle, wouldn't it be even better to use some grid electricity to further increase vehicle efficiency? Power plants generate electricity more efficiently and cheaply than using a gas engine to generate electricity indirectly through regenerative braking. So, maybe we should further augment a hybrid's power with grid electricity.

That's a promising idea, and is the basis of plug-in hybrid electric vehicles, or PHEVs. There are actually two PHEVs that are generating a lot of buzz now: the Hymotion Prius upgrade and the Chevy Volt.

Hymotion created an after-market upgrade that turns a standard Toyota Prius into a PHEV by giving it an additional battery pack that can be charged from an ordinary outlet.

The Chevy Volt has an even more innovative design: it has a pure electric drive, only the electric motor is connected directly to the drivetrain. It also has a small, gasoline-powered generator that is only used to recharge the battery pack. Because the gas engine is only used as a generator, it can run at its most efficient power level and avoid the gross inefficiencies associated with a car's engine that has to run a wide variety of RPMs and load levels outside its most efficient power range.

Lying about Efficiency

The PHEV is a surprisingly more complicated solution in part because we have no way to talk about the efficiency of this type of vehicle. We're used to evaluating vehicle efficiency by looking at miles per gallon. That works great with a hybrid, because the only energy input is gasoline, but what about a PHEV? The easy thing is to just quote an MPG number and move on, but that doesn't tell you anything.

Consider a different case. Suppose I invent a new kind of hybrid vehicle: gas and propane. It has two engines, a conventional gasoline engine and a propane engine. Together, they power the vehicle's drivetrain. When I take my new model into the EPA to get its fuel efficiency rating, I fill up both tanks. The EPA drives the vehicle on their standard course and find that the car traveled 200 miles and used two gallons of gas, so it gets an EPA rating of 100 mpg.

But what about the propane? How much propane did the car use up? How much does that propane cost? How does the use of propane and gas change with different driving conditions? We already have city and highway numbers, but maybe this new hybrid is even more complicated. How does the hybrid bit work, does it burn propane until it runs out, then switches to gasoline, or does it burn both equally over the entire range? How are consumers going to evaluate what it will cost them to drive this vehicle on their daily commute. How will environmentally-minded consumers evaluate its overall energy efficiency and carbon footprint?

Obviously, was can't just quote an MPG number for a hybrid vehicle that takes in two different fuel/energy sources. That would be misleading. In fact, unless the MPG number works in all driving scenarios, it would be fraudulent.

The same issue applies with PHEVs. If we just get an MPG number, that tells us nothing useful unless we understand how the trade-off between gas and electricity works under our individual typical driving conditions.

The Volt and the EPA

Consumers will want some sort of fuel efficiency number and consumers understand MPG, so GM talked to the EPA and argued that the EPA should use a testing regimen that will give the Chevy Volt a rating of over 100 MPG. The problem is that if the EPA allows the Volt to use the battery pack without accounting for the extra energy input, it gets over 100 MPG, but only about 48 MPG if they don't allow it to deplete the battery pack. The truth perhaps lies between these two numbers and depends on an individual's driving profile.

It's really important that the conversation doesn't stop with this one deceptive measure of fuel economy. The Chevy Volt can go 40 miles on just electricity. That's great if my daily commute is under 40 miles (and that's true for 78% of personal travel in the US according to a 2003 Department of Transportation study), but if I go over that, is it the same as driving a Prius? Unlike the Prius, the onboard engine isn't powerful enough to power the car, it can only add charge to the battery pack. If you just keep driving, eventually the battery pack will run out, and simply filling up the gas tank doesn't refill the source of power that drives the wheels. So, how far can you go? The answer is going to be complex since the gap between what the car pulls from the battery pack and what the generator puts in depends on the speed you're driving. That's not an issue with the Prius, but it's something potential Volt buyers need to understand.

The same issues apply to any PHEV that uses a small gas engine only as a battery-charging generator.

The Hidden Cost

Not only does MPG not tell us enough about how much gas the car uses, while also skipping over the cost of electricity,* it completely hides the cost of the huge compromise built into a PHEV.

The very best battery technology available today is called lithium-ion. This battery chemistry has the best balance of cost and energy density. For a given weight in batteries, lithium will allow you to store the most charge at a reasonable cost. And the cost isn't cheap, either. Lithium ion batteries are more expensive than lead-acid (like your regular car or boat battery) or the nickel metal hybrid batteries used in hybrids like the Prius.

None of these battery chemistries used in vehicles like to be overcharged or fully discharged. If you've ever left your lights on overnight and not only drained your battery, but also ruined it, you know what I'm talking about. With an electric vehicle, there's a computer that monitors battery charge state and keeps you from damaging the batteries, so you don't have to worry about it, but it does have performance implications that prospective buyers need to know about.

Consider a pure electric vehicle like the Tesla Roadster. It has a large pack of lithium ion batteries, big enough to support an EPA verified range of 244 miles (mixed city and highway). Since most commutes are far less than this, 78% under 40 miles and 92% under 70 miles, this means most driving in the Roadster will only need to use the middle of the charge range: it doesn't need to be fully charged nor fully discharged to handle daily driving. This is the best way to ensure maximum battery life. If a Tesla driver frequently uses the entire maximum range of the battery pack, the lifetime of the battery pack will be shortened. The Roadster is not your best choice as a road trip car. Fortunately, road trips represent a small fraction of travel in the US, so this isn't a problem, just something to think about when you're choosing between the Prius and the Roadster for that big road trip.

But what about a plug-in hybrid, like the Chevy Volt with a 40-mile electric range? Obviously, GM has to keep the battery weight down since the car is already packing two power plants. The Volt is designed and marketed as being pure electric for a 40-mile daily commute. If GM were to put in a battery pack that could just barely manage the forty miles, then drivers would put a full charge cycle on it every day. That would kill a lithium ion battery pack in about two years. Let's assume they want their product to last longer than that.

Since the car is designed to be gas-free for a 40-mile commute, that battery pack has to be capable of much more than just 40 miles while also bearing the burden of pushing around a gas engine, generator, fuel tank and exhaust system. So, GM decides what an appropriate charge capacity margin is, and puts in a battery pack that large.

Let's suppose they only want to use the middle 50% of the charge range, so the battery pack is only charged to 75% and only discharged down to 25% (which is about what Toyota uses in the Prius). Based on that assumption, if you drive a Volt on your 40-mile commute, you're going to use half a discharge cycle every day. You bought a battery pack that is capable of an 80-mile trip if you are willing to compromise battery life for an occasional long trip. In fact, if you could pull out all the extra weight of the gas generator, your battery pack could maybe handle a 100-mile trip. Instead, you only get the 40 miles, while still also hammering the battery pack pretty hard, and dealing with all the maintenance hassle of maintaining the gas engine.

Maybe 50% charge buffer isn't the choice that GM makes. If they pick a smaller charge buffer, the battery pack wears out sooner. If they pick a larger buffer, then they are just wasting more battery pack on a hobbled electric drive that could handle even longer occasional pure electric trips. Not matter how you slice it, trying to drive a daily commute with a small battery pack burdened by extra generator weight wastes the full electric potential of the vehicle.

Driving Pure Electric

Compare that to a pure electric vehicle with a 240-mile range. You can do your 40-mile commute with just one sixth of the battery pack's charge cycle, and you have a car that can go over a hundred miles with less impact on battery life than your daily commute in a Volt. Even a 200-mile trip is possible while leaving 20% of the charge range untouched. That's excellent battery life in a vehicle that never burns any gas and is capable of a good long drive, especially if you can get access to an outlet at your destination.

Right now there aren't many choices when it comes to driving pure electric, but that's changing. Just like when any new technology is introduced, initial models are expensive and produced in low volumes. Even the Model T was viewed as a rich man's toy when it came out. With higher production comes both better availability and lower prices. Although electric vehicles have been around longer than gas-powered vehicles, the production electric vehicle market is in its infancy, but is about to get far more interesting.

Today, you can buy a high-end, pure electric sports car with a top speed of 125 mph and an EPA-certified range of 244 miles: the Tesla Roadster, available in limited quantities for a mere $109,000. If they cost less, you probably still wouldn't be able to get one because demand would far outstrip the production rate of about 1200 per year.

But Telsa isn't in the business of solving a shortage of expensive sports cars. Their mission is to get lots of affordable electric cars on the road, the Roadster is just the start. In 2011, just months after GM is expected to start producing the Volt, Tesla Motors expects to start delivering their $60,000 Model S, a luxury sport sedan with a range of about 240 miles. By 2012 or so they expect to deliver their third model, a $30,000 all-electric economy sedan.

But Tesla Motors isn't the only one in the game. Lots of companies, both big auto makers and daring start-ups are promising electric vehicles in the near future.

Aptera expects to start producing their Typ-1e, an EV with a 120-mile range in late 2008, available initially in California for $27,000. BMW is working on an all-electric Mini-E version of the Mini Cooper, available for lease through a pilot program this year in California, New York and New Jersey. In 2009, Miles Electric Vehicles expects to begin delivery of their highway speed sedan, cleverly called the "Highway Speed Sedan," with a top speed of 80 mph and a range over 100 miles for about $40,000. Daimler has plans to introduce electric versions of both a Smart car and a Mercedes in 2010.

Brother, Can You Spare a Trillion Dollars?

Meanwhile the big Detroit automakers have resisted years of pressure to produce more efficient vehicles, instead betting their profitability on giant gas hogs. Who could imagine that either environmental or national security concerns could sour the American public on huge gas guzzlers? Combine that with the brutally obvious result of global oil production leveling off while demand has continued to grow, literally exponentially. Is it any wonder years of short-sighted profiteering have put the big American automakers on the edge of bankruptcy? All of their lobbying to prevent more stringent domestic fuel economy standards while also locking  more efficient diesel fuel vehicles out of the US market has destroyed their competitiveness overseas, and now the American buyers aren't interested in their bloated product lines either.

Their solution is to have the US Government pour hundreds of billions of dollars into the ailing US auto industry to pay for their past mistakes, while they try to retool to build incrementally more efficient vehicles based on a compromised PHEV design, hiding behind inflated and misleading MPG numbers.

That's not how I want my tax dollars spent.

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*The cost to drive a car on electricity is generally really cheap, due to the superior efficiency of an electric drive, even taking into account power plant efficiency and transmission loses. But, the cost does depend on where you live. Also, the emissions associated with the energy used in an electric vehicle vary widely depending on how electricity is generated in your area.

The good news is that we are already motivated to green up our electrical generation and EVs benefit from that without changing the car at all, while their gas-powered peers get dirtier with age. Oh, and gasoline prices can only go up, give or take short term fluctuations: global production is flattening out while worldwide demand is increasing.

Yesterday, Tesla Motors delivered their first production Roadster to their first customer: Elon Musk, chairman of Tesla's board. It has the "beta" transmission, and production will trickle out vehicles through the first half of 2008 until they have the final transmission design finished and tested.

There was a minor event marking the delivery of "P1" to Tesla headquarters, and a few members of the press were invited. According to several reports online, Elon Musk and Ze'ev Drori gave an interview and mentioned that the White Star would offer a range-extended model as well as the pure electric.

Even though this has been know for a while, this news has picked up traction and some are saying that Tesla has sold out their vision of producing pure electrics and switched to making hybrids like everyone else is doing.

This is totally wrong. To explain, I should first explain what's good about a pure electric vehicle, what's bad about hybrids and how what Tesla is doing is better than a hybrid.

Electric Vehicles

Briefly, here are the advantages of driving a pure electric vehicle:

• Much lower well-to-road carbon and other pollutant emissions.
• Zero emissions when powered from renewable sources.
• Greatly reduced maintenance.
• No more trips to the gas station.
• Quiet.
• Electric is the ultimate flex fuel.
  
• No added energy infrastructure required.
  

The biggest downsides are cost and charge time/range.

The auto industry has been mass-producing cars for a hundred years, so they have figured out how to mass produce them cheaply, or more correctly they define what people expect to pay for cars. As electric vehicles become mainstream, their costs will come down. Battery technology is currently a barrier to reducing cost, but there is lots of working going on in that area, with many avenues for significant improvement.

We have all been trained by the oil company propaganda machine to worry about the range of electric vehicles, even though most of the day-to-day driving needs for the vast majority of drivers would be met by the 100 mile range of the GM EV1 that was produced in the late 1990's.

But range isn't really the issue. Do you ever hear a car ad that brags about, or even mentions, a car's range? The range of a gas car is of minor importance because it's quick to refill a gas tank. With electric vehicles, the charge time can be much longer. But it doesn't have to be. In fact, charge time can be a huge advantage over a gas vehicle.

Consider the Tesla Roadster. It has a range of between 160 miles (worst case, driving like a maniac on the freeway) and 270 miles (mellow city driving). That's more than enough for almost anyone's daily driving. When you get home, it's just like your cell phone: you plug it in and it's fully charged long before you're awake the next morning. (It takes under five hours to charge a completely discharged Roadster with an appropriate electrical connection, significanly less if your daily commute is under 200 miles.)

Plugging in your car at night is a huge time savings compared to making the weekly trek to the gas station, and far less expensive (about 2 cents per mile).

Charge time does become an issue if you want to drive more than 200 miles in one day. The good news is that the limit to the charge rate isn't the design of the car, it's the capacity of the outlet. It's possible to charge a Tesla Roadster battery pack in about an hour if you have access to enough current. It's not practical to put such a large circuit in your home, but it would be practical to install several in parking lots at restaurants, malls, etc. So, drive your 200 miles, stop and put a couple of bucks into a charging station and your Roadster is all ready to go after you've eaten a leisurely lunch.

Once electric vehicles reach critical mass, gas cars will seem stupid by comparison. Why would anyone choose to drive a horrible pollution factory which has to be frequently maintained and manually filled with a carcinogenic and highly flammable fuel at enormous cost, most of which is sent overseas to support totalitarian govenrments?

Hybrid Vehicles

Hybrid vehicles seem like a great compromise, half way between a gas guzzler and an electric vehicle. They can in fact offer better fuel economy for smaller vehicles, but they throw out every other advantage of an electric vehicle. They still have all of the stuff from a gas vehicle that requires frequent maintenance: oil changes, muffler, catalytic converter, spark plugs, fuel filters, etc. You still have to go to the gas station periodically, and you're still running an inefficient gas engine.

But it's worse than that. In a hybrid, you punish the engine by adding the extra mass of a battery pack, reducing fuel economy and power. You also burden the battery pack with the weight of an engine and gas tank. This isn't the best of both worlds, it's the worst of both: very limited pure electric range from the battery, and poor acceleration from the gas engine.

The best of the hybrids, like the Toyota Prius and the discontinued Honda Insight, deliver great gas mileage and make for a significant improvement over the typical gas guzzler. Other hybrids are a complete fraud, offering very little in the way of improved gas mileage, instead they claim improved acceleration from the electric boost.

My wife and I do the vast majority of our driving in a Honda Insight. We've been driving one since the summer of 2001 and really like the car. But do we get the great fuel economy from the electric hybrid, or from the small aerodynamic design? I can't help but wonder if we could get better mileage from a truly optimized pure gas vehicle. I know we can do better from a pure electric.

Even through we love our Insight, hybrids are a horrible compromise. They seem like a desperate attempt by the auto companies to hold on to the revenue stream that comes from the ludicrous amount of maintenance required by a gas powered vehicle, while pandering to a growing concern for reducing environmental impact.

Range Extended Electric Vehicles

There's a variation on the hybrid design that makes a lot more sense: take a pure electric vehicle and add a small efficient gas-powered generator that can extend the range of the vehicle for long trips.

The gas engine only needs to run when you are taking a long trip, so most of the time it doesn't need to run at all. It's a small engine, and not hooked into the drive train, so the extra weight is greatly reduced compared to a traditional hybrid. Also, the engine doesn't have to run wide range of RPM and torque combinations needed for a drive train, instead it can run in its most efficient mode getting maximum power out of the gas it burns.

You still have a lot of the gas-engine maintenance issues to deal with, but you do get all of the other advantages of a pure electric, plus you can drive farther between charges for those long road trips. This could open the door to a lot of people owning a vehicle that allows them to drive nearly all of their miles in pure electric mode, without having to keep a gas guzzler in the garage for longer trips.

Tesla's White Star

Tesla's next model after the $98,000 two-seat Roadster will be the much more practical White Star, a four-door, five-passenger sport sedan that will range in cost from $50,000 to $70,000. Tesla will offer the White Star in two models: pure electric and range-extended electric. By offering these two options, far more people will be able to consider owning a vehicle that can be driven pure electric for the vast majority of their driving needs.

Look for details on the White Star to be announced in the second quarter of this year, at which point we should also get its real name. (White Star is just the code name, the Roadster was originally code-named Dark Star.)

The White Star will be followed a few years later by a higher-volume lower-cost economy vehicle, code-named Blue Star. It takes time to start a whole new auto industry, and Tesla is leading they way. I hope they succeed and inspire a great deal of competition from other car makers, either today's big auto makers or the crop of startups that will displace today's giants from the market if they don't adapt to the changing world economy and global environment.