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Developing Battery Replacement Infrastructure For Electric Cars
FathomIT sends in a NY Times profile of Shai Agassi, owner of a company named Better Place, who is working to build the infrastructure to support large numbers of small-scale charging spots for electric cars, as well as fast, automated battery swap stations.
"The robot — a squat platform that moves on four dinner-plate-size white wheels — scuttled back and forth along a 20-foot-long set of metal rails. At one end of the rails, a huge blue battery, the size of a large suitcase, sat suspended in a frame. As we watched, the robot zipped up to the battery, made a nearly inaudible click, and pulled the battery downward. It ferried the battery over to the other end of the rails, dropped it off, picked up a new battery, hissed back over to the frame and, in one deft movement, snapped the new battery in the place of the old one. The total time: 45 seconds."
Swappable batteries will stop being cool as soon as the iCar comes out, anyway.
When you buy a litre of petrol, it should take you a set distance. When you fill up on LPG, Hydrogen or whatever, the same is the case. There is one important factor in the battery swapping idea that is fundamentally different though. Batteries degrade and can at times do so in strange ways.
Say, for example, that someone has let a spare battery sit idle for some months, charges it up at home and, knowing it's rubbish now, goes off to the nearest fuel stop to change it. Automated process charges it, dispenses it. You get stuck on the freeway after only a few kilometres.
If you stick to your own battery, then you can tell the condition of the battery over time. No dramas. Even with thorough checking though, battery changing services have a lot of questions in regards to reliability and liabilities if it is to work. Who picks up the tab for a dead battery? The owner or the 'fuel' vendor?
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Toyota has reported replacing none of its hybrid batteries in the 8 years that hybrids have been sold in North America (due to wear and tear). In other words, the rumor you heard is just that -- a baseless rumor.
The myth of poor battery reliability in hybrids is not bourne out by the real-world experience of hybrid taxis around the world. Specifically, the fact taxis have travelled 240,000 or even 300,000 miles with no major problems with the batteries or any other component of the hybrid system.
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Ah, but which battery did they replace? The Prius uses a small Lead-acid battery for the gas engine in addition to the big main NiMH battery pack used for the electric motor.
Depending on the environment, the Lead-acid battery can need regular replacement. The NiMH battery should not need replacing unless it was defective.
Ah, the "long tail" argument -- that old zombie of electric vehicles. No matter how many times you knock it down, it comes coming at you.
Power plants are more efficient than internal combustion engines. While the engine itself can *peak* at a fairly high effiency number (percentage-wise, as much as the upper 30s for gasoline and mid 40s for diesel), that's not what you get in practice, as that's only for a narrow torque/rpm range. In practice, you also have parasitic and braking losses. Total well-to-wheel consumption is about 14% for gasoline and 17% for diesel. Engines are slowly getting more efficient, but at the same time fuel production is getting *less* efficient as we have to move more to syncrude and deepwater (think tar sands and outer continental shelf). Power plants, however, are only getting more efficient, and fairly rapidly. Well-to-AC power for an average coal plant in the US is 32%, and natural gas is 42%. Those numbers are higher in Europe. Next gen coal plants are over 40% and next-gen natural gas 60%-ish. Coal, the dirty fuel, is only half our generation. After that is natural gas (a very low carbon fuel per unit energy) and nuclear (a near zero carbon fuel). After that is hydro and then wind (both near zero carbon). There's also a smattering of other generation methods such as diesel, solar, geothermal, and biomass that combined make up a couple percent of our grid.
AC power transmission in the US averages 92.8% efficiency. Your typical EV charger is 92-93% efficient (rapid chargers, closer to 90%). Li-ion batteries are generally 96% (rapid charge) to 99% (trickle charge) efficient. Electric drivetrains average 85-90% efficient (they can peak at over 95% on a really good one). And regen braking is pretty much standard. So your net well-to-wheels efficiency is very high, and your carbon is low. And while petroleum gets dirtier, the grid gets cleaner. Last year, for example, over 2/5ths of our new power that went online was wind, and most of the rest was natural gas.
But wait, it gets better. Most EV charging is done at night, on a timer to take advantage of low off-peak rates. Coal power plants take a while to ramp down. In the process, you can sometimes get what's called "spinning standby" -- power generation capacity that's literally wasted because there's nothing to consume it. This mainly occurs in the evenings. Charging off of it is literally free of environmental consequences. Furthermore, most power plants run more efficiently at higher capacity. Evening out the day/night peaks makes the grid as a whole more efficient.
Perhaps having a DOE study conducted at PNL explain it to you will help. Here's a graph comparing the efficiencies of different drivetrain options, and here's one for emissions.
Can this zombie of a notion please accept its headshot and stay down?
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You need to give a bit more justification than 'it can be done' if you want people to take you seriously. RTGs have a terrible power to weight ratio. The best one in the article you linked to is around 0.06W/Kg just for the power source. Let's assume that this is a terrible design and we can improve on it by an order of magnitude, giving 0.6W/Kg. Now let's assume that the car and passengers weigh nothing.
The formula for kinetic energy is E = 1/2 mv^s. By dividing both sides by a time factor, we get P = 1/2 ma^2. Divide through by mass, and we get P/m = 1/2 a^2. Substituting in the value from the RTG output (Power / mass) we get 0.6 = 1/2 a ^2, or a = sqrt(1.2), approximately 1.1 metres per second per second.
Remember that this is for a massless vehicle with an RTG with an order of magnitude higher power output than any that anyone has built so far. It would take a little over 26 seconds to reach 60mph. Even a fairly rubbish battery powered car can reach 60mph in under 10 seconds - this hypothetical RTG-powered car would take 13 seconds to go from 0-30mph, which is a dangerously low acceleration for most urban roads. And, note, that this is assuming that the (massless) engine is also 100% efficient. In the real world, you would be lucky to get a tenth of this acceleration, so you'd take more than 2 minutes to go from 0-30mph. Not really a very practical solution.
RTGs are great for applications where they do not have to move (or, as with spacecraft, where the motive force comes from elsewhere), or which have a constant power drain. They are incredibly badly suited to automotive applications. Betavoltaics, as I said, are potentially a viable solution, but RTGs are not. Just because something can give 40W for a number of years does not make it a good replacement for something that gives several kW for a few hours. Sure, the energy output may be the same or greater, but the power output is much lower.
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