Unsuccessfully Greening Public Transport


Skiing Break was action packed for the kids. Monday museum, Tuesday playland, Wednesday skiing with grampa, Thursday swimming, Friday museum & puppet theatre and a museum-organised LAN party for the 10-y-o.

Yesterday's museum was the Public Transport Museum which shares an entrance and a ticket with the Toy Museum. Lots of buses and trams, including one bus standing on a service pit where you can descend and check out the under side of the vehicle. Juniorette and I made a pink train carriage in the children's workshop.

One thing that caught my eye was a mothballed experimental hybrid bus, part of a long-running project to improve the environmental footprint of the city's public transport. It has a car engine running at constant RPM, which charges a large battery, which in turn drives an electrical engine, which drives the bus. Among its strengths is an ability to drive silently in sensitive areas. Among its weaknesses: a 110% fuel consumption compared to a normal diesel engine. Back to the drawing board.

According to a signpost, the fuel-guzzling hybrid is just one of a series of designs that have fallen by the road side during the project. The best solution so far has turned out to be ethanol buses, which are quite common, unmistakable with their smell of old drunk. But as everybody knows by now, ethanol is a useless replacement for fossil fuels as its production uses up loads of them. So it seems that the Stockholm program has yet to find even one working solution. Good to know that they're trying, though.

In the future, we may see buses running on methane from the Henriksdal sewage plant. It's inside a mountain that my commuter train passes through every day, and the housing area on its top (once the site of a 1st Millennium hillfort) is colloquially known as the Toilet Lid. Hope that idea pans out.

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There is a great deal of popular misconception about hybrid drives, primarily because of the relative success of the Toyota Prius.

Several manufacturers have found that it is far from a magic bullet, the extra weight and complexity of hybrid drives come at a price (the Prius, a highly optimized design, would be very efficient with a conventional drive). Quite a few hybrid drive vehicles are not considered high efficiency by the EPA

That is why I was disturbed when a candidate in our recent election was proposing mandating that manufacturers offer hybrid drive at the same price as conventional systems. This is a terrible solution because, due to the thousands of dollars of extra cost of the hybrid, to not lose money, the manufacturers would have to raise prices for everyone to acheive this dubvious equity. Also millions more large batteries would need to be produced (and disposed of), the fiscal and environmental implications of which are quite fuzzy right not.

Having started out as a physics major many years ago, this does not surprise me. Simple physics dictates that there will be some loss of energy when generating the electricity, and some loss when using the electricity to drive the wheels. One can gain energy with a hybrid by generating electricity when breaking and various weight-saving measures can reduce the energy required.

Also, I think a great many people don't think about the environmental impact of plug-ins. If we build huge solar plants in the desert, it will almost certainly lead to the extinction of some desert species, and there will still be lots of energy loss in the transmission of the power over long distances. Given equally efficient generators, it should be more efficient to generate the power locally (i.e. in the car). Of course, larger generators tend to be more efficient, so this can go either way.

Like Jay, I also have concerns about the environmental and economic impact of all those batteries. Does anyone have any good figures on how long the batteries last and what the replacement costs are? Last time I bought a car, I figured that given how little I drive, it would take more than 10 years with gas at over $10 a gallon before I would break even given the price difference between the least expensive hybrid and the somewhat larger Scion xB (the original one) that I wound up getting. I suspect the batteries don't last anywhere near 10 years, but I have yet to see any figures.

I'm having a hard time with seeing the downside to a hybrid bus that uses regenerative braking to charge the battery and then uses the same wheels to drive the bus. The only added cost is the batteries, which don't need to be very large to capture the energy of a (typically low-speed) bus braking to a stop, and the rest of the power train is unaltered.

Sounds to this engineer like the mission objectives were too ambitious when a more modest goal would have been achievable.

By D. C. Sessions (not verified) on 28 Feb 2009 #permalink

Edward: Thanks for all your skepticism. But really, the status quo is demonstrably, well, terrible. It's fine to say "alternative X has this flaw or that flaw", but that is really pointless unless you compare it to (a) the status quo, or (b) some other alternative. It's like talking on and on about how radiation isn't really very healthy, when your audience consists of cancer patients.

And lastly: Given equally efficient generators, it should be more efficient to generate the power locally (i.e. in the car)

This is not obviously true. You have to also compare the cost of dragging a heavy generator around with you, versus carrying just the stored energy (batteries, hydrogen, something else...)

Hybrid buses so far were not very successful because they tried to use lead-acid batteries and they are far too heavy and inefficient.

New li-ion batteries are much better in this regard. There's a pilot project in Canada, and so far new hybrid buses have about 30% better fuel economy than common diesel buses.

Another alternative: completely electric buses. They are successfully used for some short routes (like moving between airport terminals, etc.)

By Alex Besogonov (not verified) on 28 Feb 2009 #permalink

I'm having a hard time with seeing the downside to a hybrid bus that uses regenerative braking to charge the battery and then uses the same wheels to drive the bus.

This is not to say that the idea can't work, but it's not that simple. How much of the bus' energy is braking for stops vs air resistance and other rolling losses? Regenerative braking works best when the vehicle can decelerate, going to a full stop at frequent intervals requires lots of use of brakes anyhow. Additional weight and cost is a factor, as well as the fact that hybrid systems generally use a motor/generator combo. Unfortunately the factors that make a motor efficient work against it in generator mode. (as opposed to a diesel-electric locomotive where the traction motors drive and do not generate)

It's a lot more subtle than people realize. The algorithm managing the charge system is quite empirical and the word is that at least one major auto company found out that a simple efficient diesel was actually more efficient than the same car with their high tech experimental hybrid system.

It's not public transport, but there is a company in Aus that is converting cars to run on electricity only.

They take out the petrol engine and tank and put in batteries and an electric motor. The one featured in this video http://www.youtube.com/watch?v=ykqhigH19-E is owned by someone living in Trentham, in country Victoria, a bit more than 100km from the Melbourne CBD. The batteries are recharged from the solar panels on the roof of his office.

Trentham is not far from where I live. We get plenty of long hot sunny days in summer (although the panels may not be working very well at the moment because of all the smoke in the air from the bush fires), but the winters are overcast and dreary with occassional snow.

The jounalist who wrote this article is the owner of the car in the video.

This is a shorter piece from one of the local newspapers.

Back to buses, Melbourne has some that run on ethanol, made from sugar cane, grown in Queensland. I don't know how efficient they are, but I have never noticed the smell you mentioned, Martin.

By eleanora. (not verified) on 28 Feb 2009 #permalink

Compressed air cars! The way of the future - convert mechanical energy directly to mechanical energy and avoid the costly step of making electricity to drive the car. And we wont run out of compressible air in a hurry.

Kevin: Since it isn't clear from my original post, I am in no way supportive of the American SUV status quo. It seems to me that there is no reason most people can't drive cars that get at least 30 MPG now (if the manufacturers made more of them) when they have to drive at all. I actually prefer to bike or take public transit to work. I was speaking from having tried to figure out the pros and cos of buying a small fuel efficient car vs. a hybrid. Long term, everyone having even a small car each probably isn't sustainable, but we need to reconfigure our cities and systems so people can do things like weekly grocery shopping without a car.

At the same time, I feel like a great many advocates of solar and wind fail to see that those sources have negative impacts as well. Recently I was talking with someone who said words to the effect of "there is no problem sticking lots of solar plants in the southwest. There is nothing there but desert." Having once had a friend who was a desert ecologist and who studied the impact of housing developments on desert species, I think most desert ecologists would disagree with that sentiment. I think most people just don't comprehend how much land would be required for solar. I've found this to be a fairly sober assessment of many of the issues: