Betterplace dies -- how do you make an electric robotic taxi fleet?

It seems that Better place has gone to... a better place to put it ironically. I'm not greatly surprised, I expressed my skepticism last year.

But I do believe in the idea of the self-driving electric taxi as the best answer for our future urban transportation. So how do you make it happen?

There's a big problem with this vision. Electric cars today have perhaps 100 to 150 miles of range, which means 3 to 6 hours of operation, depending on the speeds you go. You can make more range (like a Telsa S) but only by adding a lot of weight and cost. But an effective taxi is on shift all day, or at least all the waking hours, and could easily operate 8 to 10 hours per day. While any taxi will have downtime during the day (particularly at off-peak hours) the recharge of the battery takes so long it's hard to do during the day. Ideally you want to charge at night, when power is cheap. So let's consider the options.

Large battery pack

You could make a vehicle with enough battery for a full day's work, and charge it at night. This is very expensive today, and also takes a lot of room and weight in the vehicle, reducing its efficiency. You also need taxis at night so either way you have to have some taxis that work at night and recharge in the day, but not as many.

Battery swap

While battery swap did not pan out for Better Place, it actually makes much more sense for a robotic taxi fleet. You just need a few swap stations in the city. It doesn't bother the robots if they take a while for a swap (mainly it bothers you because you need more stations.) And while humans would get very angry if they came to the swap station and saw they were 4th in line at 5 minutes/swap, robots would just schedule their swaps and get in and get out.

That's all good, and it solves a few other problems. Taxis will be putting on lots of miles every day, and they will probably wear out their battery quickly. If the rest of the vehicle has not worn out, swap becomes ideal -- replace the vehicle's components when you need to, including the most expensive part, the battery. It also makes it easier to charge all batteries only at night, on cheap baseload power.

Swap also allows the batteries to be only used in the "easy" part of their duty cycle (from 80% to 20%) without much hassle. You only get 60% of the range, but you don't care a lot, other than in having to buy more battery packs. You just do the math on what's cheaper.


A working supercharger that can recharge a vehicle in an hour solves the problem as well. Robotic taxis can always find a spare hour without much loss of efficiency. (Indeed with none as they will age by active mile or hour.) The big problem is that supercharging generally is felt to stress the batteries and reduce the lifetime of the packs. Certainly running a car on full cycle every day and supercharging it is not going to produce a happy battery.

A robocar supercharging station could do a few extra things, though. For example, you could hook the car up to a special cooling system to pump externally chilled coolant through the batteries, as heat is the big killer in the supercharge. You might even find a way to put some pressure in to keep the cases from expanding that much, as this is a big stressor when charging.

Supercharging probably has to be done in the day, with more expensive power. One charge for the morning peak and another for the evening. Some speculate it's worth using your inventory of old battery packs to store power during the night to release in the day. Solar can also help during the day -- on sunny days, at least.

While automated connection is good, you really would not have many supercharging centers, due to their high power needs, so they could have human staff to do the work.

Both the supercharging and battery swap stations do not need to be located all that conveniently for humans. Instead, you can put them near power substations where megawatts can be purchased.

More vehicles and ordinary L2 charging

If the batteries are more expensive than the vehicles, then perhaps just having more vehicles to house all your battery packs is the answer. Then you have vehicles spending their time idle, and charging at ordinary level 2 (6kw) rates. Full level 2 can add about 20 miles of range to a car like a Leaf in an hour. Depending on the usage patterns that might not be too bad. Of course it's daytime power again, which is expensive. Urban taxis won't go more than about 25mph on average if they are lucky, often less, particularly at rush hour. Suburban will go a bit faster. You need stations that allow a robot to recharge, which could mean inductive, or human-staffed, or eventual robotic plug-in systems. Don't laugh at the idea of human-staffed. The robot will not be in a super rush, so stations near retail shops or existing gas stations would work fine as long as somebody can come out and tend to the robot on connect and disconnect within 5 minutes.

It may seem like more vehicles is more expensive, but that's not necessarily true. It depends on how and why the vehicles wear out. Ideally you design the vehicle so battery and most major vehicle components all reach end-of-life at a similar time or that they can be replaced easily. That may mean a battery that can be swapped -- but in the shop, not at an automatic swap station.

Plug in hybrids?

Plug in hybrids of course solve the problem, and they can charge when they can to be mostly electric and only use that gas engine more rarely. This actually creates a downside -- it's expensive to have a fossil fuel power train around to barely use it. And it adds a fair bit to the maintenance cost. This does allow for highway travel. Otherwise, you send a liquid fuel car to anybody wanting to do a long highway trip - save the electrics for the urban travel.

Very light vehicles

Today's electrics use about 250 to 300 watt-hours/mile. OK, but not great. Efficient designs can go below 100 watt/hours per mile. That means doing 300 miles, which is enough for a full day in a city cab, needs only 30kwh (probably a 45kwh battery.) That's a $22K battery today, but it will be a $9K battery by the end of this decade according to predictions. This might be quite reasonable.


I think plug-in and VLV (1-2 person tandem) are the way to go. Plug-ins are already made, require nothing new, plug in at night. These will be the first ones. Then get busy designing / building the small 1-2 person enclosed motorcycle, 3 or 4 wheels. I think it is something like 70% of trips are 1 person and like 90% with max 2 people. Very few buy these type of vehicles now because of the lower utility and high price - due to low volumes. A taxi fleet owner can custom design for the purpose and order in bulk to get a good price.

A fleet will have many vehicles. A large fraction will be for 1-2 person urban trips, but vehicles are needed for peak demand of trips with more people or cargo or whatever. Because you can always send a sedan for 1-2 people if you have to, but you can't send a small vehicle for 3 people, you have slightly more larger vehicles than you need, but it's not that bad.

However, this is long term. Short term we must depend on what the car industry makes efficiently and cheaply, and that's 4-5 seaters. They must also be crash-worthy. The economies of scale in car mfg are huge. If you are just making 1,000 your 2 person vehicle will cost more than a Leaf, but once you are making 50,000 it's a different story.

My understanding is that Tesla has shipped over 10,000 vehicles (counting both Roadster and Model S). The small battery pack, 160 miles at 55 mph under ideal conditions variant was never physically produced (although a small number of cars, probably several hundred, are software limited to that.) Do you have a source that indicates that the Nissan Leaf plus Ford Focus Electric plus Mitsubishi MiEV etc add up to more than 10,000 units ever shipped? (I assume we can exclude the Volt?) I suspect that at some point in 2013, we will reach a point where Tesla has produced more pure EVs than all the legacy automakers combined.

My understanding is also that Tesla says that you can Supercharge as much as you like without worrying about battery damage; the only thing you need to watch out for is that you not regularly charge the battery to more than about 85% or 90% full. (This is the ``standard charge'' vs ``range charge'' setting on the touchscreen.)

Elon has reported (fall of 2012, possibly in the Foundations interview on Youtube) that if you look at the weights of the metals that go into a battery pack, and what those metals cost as raw commodities, that the raw materials for a battery pack for an EV cost about $80/kwh. Turning the raw materials into a battery pack obviously does cost something, but Elon seems to think that those manufacturing costs can be driven down by a lot.

(Additionally, we seem to be discovering new lithium mines, and in some cases, it appears that they may be more efficient to operate than the existing major lithium mining operations, which might drive the cost of the raw materials down.)

I think the long term future is going to be solar. If the prices keep dropping, solar panels will eventually be cheaper than the current electric monopoly distribution charges, and I don't expect the electric monopolies to have a culture capable of figuring out how to reduce the distribution charges. The assumption 10 years from now should be that we need to be able to charge EVs from abundant solar panels.

For the typical personally owned vehicle, we should figure out how to embed 40% efficient or better solar panels into the paint of the cars, so that all you need to do to cover your regular commute is leave the car parked in sunlight during the day. (A Tesla requires less than 400 wh/mile, and 40% efficient solar panels are likely to deliver something like 400 w/m^2.) Of course, that doesn't cover the taxi case, but if the lifespan of the vehicle is proportional to the miles driven and not calendar time, and we're optimizing for minimizing energy use, then one round trip per day per car from the suburbs to a workplace should be more efficient than sharing one car between two such commutes, with a lot of empty miles in between. (But I also thought I'd seen Tesla claiming that battery life was going to be more proportional to calendar time than usage.)

Another interesting question is whether concentrated photovoltaic solar might be a reasonable option for charging: if you park the car someplace where mirrors passively direct extra sunlight to the car, and the car has high efficiency solar panels built in, does that increase the charging rate by a useful amount?

I suspect you're right, that Tesla could surpass the other EVs, at least for a while. Tesla's success will inspire some competition. The big car makers never expected there was that level of demand for a $100K electric car.

The old prevailing wisdom was that charging that fast hurt battery life. Will be great if they get around that. A robocar supercharging station does not have to be super conveniently placed. It can be located next to a power substation to get the megawatts it needs. (The solar panels should be elsewhere, like New Mexico, if you are going to put them in.)

Charging EVs from solar panels is a tall order. The superchargers go up to about 90kw. That's a lot of panels to have per station in a supercharging station! Again, put panels in New Mexico where they do the most real good -- offsetting coal and running at high efficiency, and not in California where they just offset NG or the northeast where they don't get good insolation.

Solar on a car is a very bad idea. Even if you could get a 40% panel (which would be a huge breakthrough) that's only 400 watts when pointed at the sun. It's much less if flat (like a car roof) and parked in the shade (not all spots are sunny) and worse, once the batteries are up to medium levels you start discarding all that power! What a terrible waste. Much better to put the panels up next to sunny coal plants, tilted to latitude where they do some good. Put concentrators there if they make sense. (They don't always because the extra heat reduces efficiency.)

"The big car makers never expected there was that level of demand for a $100K electric car."

But the $100K market was never their target business, whether it was electric, gas, diesel, hamster, whatever. If they had been able to build an all-electric car for $20K you bet we'd have seen it.

The Leaf is under $20K with the subsidies here in California.

Right now batteries are expensive, and in fact electric cars don't save you money because of that. This means even a minimal range car is expensive (pre-subsidies) like in the $30K+ range, but frankly the range of this cars is not satisfactory to US buyers.

What Tesla figured out was that you should go high end. Instead of saying, "Crap, this battery is going to make the car cost a fortune, let's scrimp everywhere else to sell to the people who are willing to overpay to be green" as the other automakers said, Tesla said, "Let's make the car super high-end, no scrimping, and sell to people willing to overpay for the best car they can get."

Telsa is right, there are a lot more of the latter people.

In fact, I would bet there are a number of people buying a Tesla S (or bought the roadster) in spite of the fact that it was electric (and thus has range and recharging issues) rather than because it's electric (and thus is greener and cheaper for the energy per mile.) To be fair, they are buying it because it's got the performance that comes from a high-power electric car, but that was not the reason most car makers thought people would buy electric. Nissan would have done better making an Infiniti Electric like the model S than making the Leaf, and Chevy would have done better with a Corvette than a Volt.

In many cases, new trends in cars have propagated from the top down, not from the bottom up. Henry Ford and his Models T and A are perhaps an exception. In many countries, automobiles were at first toys for the rich then gradually became more prevalent. We can see that happening in China today, where many makers sell their high-end cars rather than the low-end.

Add new comment