The discussion centers around Tesla Motors' claim of a "well-to-wheel" efficiency of 1.14, with participants questioning the validity and implications of this figure. The conversation explores the definitions of efficiency, the energy costs associated with battery production, and the sources of electricity used to charge electric vehicles, touching on theoretical and practical aspects of energy efficiency in automotive technology.
Participants express multiple competing views regarding the interpretation of Tesla's efficiency claims, the relevance of cradle-to-grave energy costs, and the validity of the reported efficiency figures. The discussion remains unresolved, with no consensus reached on the implications of the claims made by Tesla Motors.
Participants note that the discussion involves complex factors such as the energy costs of battery production, the efficiency of different energy sources, and the assumptions underlying the efficiency calculations. These factors are not fully resolved within the discussion.
Ivan Seeking said:They certainly aren't including the cradle to grave energy costs.
How much energy does it take to make 900 Lbs of Li ion batteries, and how are they recycled.
DaleSpam said:Look at the units. That is 1.14 km/MJ efficiency, not 114% efficiency.
Phrak said:Thanks, DaleSpam. Blind spots, you know.
Something else is a bit odd. They quote a "Source Fuel" of natural gas, while 49-51% of US electricity is generated with coal. However, they are located on the west coast, in California with electricity generated from
Natural Gas 45.2%
Nuclear 14.8%
Large Hydro 11.7%
Coal 16.6%
Renewable 11.8%
A minor swindle, I suppose.
Fabius said:The energy cost of production of the system isn't part of the system efficiency calculation, it never is.
The well to wheel efficiency is a measure of how much of the available energy contained in whatever raw material used for fuel actually makes it to the driving wheels of the car.
... and Tesla published a blog about receycling of the Li-Ion cells: http://www.teslamotors.com/blog4/?p=66
Fabius said:Hmmm.. using figures for the fuel source predominant in their major market... scandalous! Of course they should be making their figures look as bad as possible like every other car maker, right?
Phrak said:Those of us who are objectively intested in these things would prefer facts over fiction. So what, you don't care or you prefer the fiction?
The source of electricity when you plug-in your electric car is the elecrical grid. That source is not exclusively natural gas, and unlikely so if you live in the eastern United States. Unless I've missed yet another point, to claim a souce of power such as natural gas is somewhat incredulous.
kmarinas86 said:If you look at the table on the webpage (http://www.teslamotors.com/efficiency/well_to_wheel.php ), the last two rows show cars whose source fuel is natural gas. The wheel-to-well ratio decreases as you go down the table. The table suggests that the selected natural gas burning cars provide less efficiency than the selected gasoline burning cars while having slightly less well-to-station efficiency. [\quote]
Apparently the 86% well-to-station efficiency for the Honda CNG is energy cost for transportation and compression before it arrives at the dealer. Then the 81% number for gasoline is the energy lost in refining and delivery.
The well-to-station efficency for the Tesla roadster is the lowest of all in the list, yet the car itself is remarkably more efficent than the other cars. That's no surprise either, because the Tesla roadster is electric.
This number of 52.2% efficiency for "well to station efficiency" is actually another one that should be suspect. It suggests a 52% efficiency in generating, transporting and converting electricity from natural gas to where it arrives to charge the car. I think this number is only realistic if the waste heat from the turbine is utilized for heating. Waste heat utilization is represtented in only a small fraction of electric power generation plants.
Overall, 30% to 35% is closer to the delivered energy efficiency of power generated via a heat engine. If they insist upon quoting natural gas, sources such as hydroelectric and atomic power shouldn't enter into the calculation.