As it happens, my friend's car was crashed and he decided to replace it with an environmentally friendly model. But how to make a choice? He called me and asked what is 'greener':

• a car with a diesel engine;
• an ethanol-driven car; or
• a hybrid car.

I did not have an answer so I posted this question to the IIIEE alumni network. Amazingly, I have received more than 15 answers within a couple of days. Here is the selection of the most interesting ones (slightly edited for style).

See also a sequel

Answer 1

Depends on driving pattern, but for milk-carrier type of driving (lots of stops and starts in a city) I'd go for Prius. Many kids and long distances I'd go for a diesel but make sure that it can run on biodiesel (vegetable oil based), that is what I drive it is a Seat Alhambra for 7 persons, I fill it uo with RME (biodiesel). Etanol is sort of an OK middle way I guess, and especially if he also is concerned about performance, acceleration etc. as etanol outperforms there. Hehe, he could buy the new Koenigsegg Flowerpower that runs on etanol but it costs a couple of millions, SAAB Biopower is a good etanol car.

Answer 2

I would suggest this hierarchy:

• diesel - any car that can also tank bio diesel and does not have too much horse powers (100 hk is lagom for city and 150 hk for more use on highways) -- he must go and ask bilhandlare
• hybrid - this one is expensive but it has good envir. profile and is much better in terms of emission in the city . Prius is the best choice, although now there are more choises too. Motormännensriksförbud has a web site and there they explain which car is good / bad.
• etanol - well, I am not sure about the LCA of each km, but what is clear that ownership costs and costs per km are the same as driving gasoline car. - you simply need more etanol per km than besin...

Answer 3

Definitelly the hybrid!

Answer 4

I have owned both A Prius and a Volvo 1,8 flexifuel and a diesel with particlefilter.

The Prius

good for city driving. Batteries are used at low speeds. Regeneratic braking recharges the batteries when braking the car. Nice comfort and room Environmental rebate from the gov´t of 10000 and free parking in the larger cities.	Expensive to buy Average consumption is about 0,5-0,6 liters/10 km. But it is still a fossile fuel and emissions of CO2 are there

Ethanol car (flexifuel)

Diesel

• With particle filter the particles are kept low+Great power and torque Low consumption Cheaper than gasoline	Expensive to buy Still a little higher taxed No parking or environmental rebates unless the consumption is very low (citroen C2 or VW lupo for example)

  Answer 5

  The best car in Sweden in 2006 from the environmental perspective was Ford Focus Flexifuel running on ethanol (E85).

  You can read the report here (in Swedish, I guess your friend is Swedish?):

  http://www.gronabilister.se/public/dokument.php?art=511&parent01=1&parent02=&parent03=&stat=1

  The assessment was made based on an LCA approach.

  The thing with Prius is that we normally think that it must be environmentally friendly because it is a hybrid, but at least from the consumption point of view, gasoline hybrids are just as efficient as normal diesel cars.

  Gasoline hybrids are therefore more appreciated in the markets, where diesel is not popular (like the US).

  For Europe the best hybrid would be a diesel hybrid (probably to be expected in 2009/2010). And running on 2nd generation biodiesel would make it even better!

  But for the time being, as I said, Ford Focus Flexifuel seems to be the best one.

  Answer 6

  [with diesel ...] there are far too much dust and other harmfull emissions involved. The point with the ethanol is, where does it come from. Our german rapeseed biodiesel is not less problematic for the climate than good old oil. When the swedes get the ethanol from wood this is great, when they get it from sugarbeets, grain or even from brasilian sugar cane this is problematic.

  Hybrid is interesting, but the great energy saving effects do happen mainly when your colleague is driving mainly on lesser roads or in cities. The savings in long highway travels are not so big. Here in Germany it is further the aspect, that hybird cars are rather noisy at high speeds but very quite at low speed. But as you arenŽt allowed to drive fast in sweden, this is perhaps another advantage for the hybird.

  What I dont get is why there is no chance to take a hybrid and build in a natural gas tank system for the fossil part. This combined with a rational driving style could come into sustainable regions.

  So as usual no answers but more questions. The german group VCD (www.vcd.org, sorry all in German) does rate cars by their ecoefficiency. They do also take the driving style into consideration. When you can get support by somebody speaking german this is a very good inforamation source.
  

  So good luck and always remember the best car is a bicycle (says me who drives 50.000km/a by car)

  Answer 7

  From a most basic - theromynamic performance - point of view, nothing yet can compare with a fine diesel engine. Its overall efficiency is the best. With the hybrid, you've got huge problem with the battery section, especially id you assess it from a life-cycle perspective on the materials (and their exergy) involved. the Prius, according to some assessments, is not a better option from some lighter SUVs. Ethanol? When it is shipped to Sweden from Brasil? One must be really weird to believe this hype.
  My suggestion is to go for a small turbo-diesel engined car with 5 or 6 gear transmission. The lighter the car is the better. For reliability reasons I'd go for a Japanese one, like a Toyota Corolla (1.4L D), a Mazda 3 (1.6L D), a Honda Civic (1.7L D). This if he/she wants to get something used. If something new, then even these models now come with a bit "improved" larger engine; however, I'd still consider them the best option. If into European cars, then I'd go for a Volkswagen Golf with the smallest available turbo-diesel engine.

  Answer 8

  • • I would go for a diesel.
      Audi A3 1,9 TDI is classified to emitt less than 120 g (0,45 l/swedish mil) and he will therefor get 10 000 SEK back from vägverket if he purchase a new one. Nesté in Finland is venturing to produce biodiesel and the first generation of biodiesel with a 20 % blend of organic materials is on sale at Q8 gasstations.
      The decision depends on how much he drives though. A diesel is expensive to buy and he needs to put down 1500 mil a year to break even compared to a gasolin fueled car.
      Audi A3 is exactly as a Golf in size.
      If he buys a larger car I would considder a Toyota diesel. Toyota has the most effective particle filters at the moment and are fuel efficient as well.
      

      Answer 11

      
      

      The following web page might be of use - http://www.miljofordon.se/index.asp with e.g. lists of which cars are classified as environmental and qualify for a subsidy (10 000 SEK), as well as info on alternative fuel stations etc, as well as a possibility to compare different kinds of vehicles. http://www.miljofordon.se/latta/

      Unfortunately, the English version of the page lacks a lot of the information that is available in Swedish.
      

      Answer 12

      Background data and calculations

      I think we can assume that all three cars have almost same standards for emissions other than fossil CO2. The hybrid uses about 50% less fossil fuels than the average standard car (about 8-9 liter petrol per 10km). This means about 4 liter petrol per 10km. The diesel can reduce fossil fuel consumption by about 30% in comparison to an average car standard car. This means about 6 liter fossil diesel per 10km. The ethanol car reduces fossil fuel consumption by about 85% but it also includes transportation to grow it and get it here from Brazil so let’s say about 60% reduction. This gives about 3 liter petrol per 10km. If we your friend is driving mainly in town the hybrid would be better than both the alternatives since it uses only the electric engine at speeds below approx. 50 km/hr. ConclusionsAvoid the diesel since it reduces CO2 less than ethanol and hybrid. Take a hybrid if you mainly drive in town and an ethanol car if you drive more mixed driving. But it is not so simple – The future will bring better car alternatives

      
      

      Neither of the three mentioned alternatives is long term sustainable. You could not convert all cars to either of the three alternatives and expect the car fleet to be sustainable. Fossil petrol prices will soon enter into a permanent upward trend as we will not be able to pump up enough crude oil to meet the demands of the emerging global economy. Ethanol prices may also go up within a few years when it gets harder to harvest enough ethanol to meet the demand. There are some things that can be done to both increase the efficiency of ethanol cars and to increase the output of etanol per area of biomass land. This means that whatever car your friend chooses it should be seen as an intermediate step to later more cheap and long term sustainable solutions. The car of the future will be an electric engine since the electric engine is much more effective that the Otto engine that standard cars use. The electricity will come from several sources but one good solution as batteries improve will be to load the car over night by plugging it in to the electric grid (this is called a plug-in electric car). If you then buy green electricity (from hydro and wind power for example you will have very little CO2 emissions from you driving. Another option will be to let wind and hydro power generate electricity and then convert that into chemical energy (hydrogen gas) through electrolysis. The created hydrogen gas then can be used either as a fuel in itself (but it is explosive and very fluent so it is hard to distribute) or converted to methanol. The emthanol will then be transformed back to electricity in the car through an inverted electrolysis in a fuel cell. Why go back and forth between chemical and electrical energy like this? The renewable energy sources are often not available when they are needed. The sun might not shine when we want to drive etc. It therefore makes sense to store the sunshine in a chemical energy form and then use it when needed.

    
    

    Your friend can exclude the diesel car, except if he wants a very small one. Only the smallest can compete with Toyota Prius. Choosing between Prius and ethanol is not that easy. First one has to ask where the ethanol comes from. A question of LCA. Guess ethanol in Sweden is OK. But if the friend is swedish he could consult www.gronabilister.se.

    Answer 10

  A good comparison tool is to be found in Icelandic on: http://www.orkusetur.is/Apps/WebObjects/Orkustofnun.woa/wa/dp?id=1916 Bifreið 1 means select car 1 and Bifreið 2 means select car 2. You select car manufacturer and make and type. On the top you insert how much you intend to drive and the calculator gives you results in one year. You can also select to see how many trees you should plant to balance the carbon you will emit according to your selections. What it does is to compare the car you select to check to any other car you also select. It does not go on LCA ( probably because most of the cars of similar size add up to similar material and energy consumption during the manufacturing time (yes I have a sceptical view on those who say that Prius adds up to higher environemental impacts than other cars of similar status, - inspite of media attention to a different view).

  But why does not your friend check methane gas cars?

  Answer 9