Last weekend we reported on Singapore’s Land Transport Authority (LTA) slapping an important tax surcharge on the Tesla Model S after running some emission tests and rating its energy consumption at 444 Wh/km. After accounting for Singapore’s grid emission factor of 0.5 g CO2/Wh , the LTA determined that the Model S somehow ended up on the worst end of the global city’s scale for vehicle pollution (C3 band).

Tesla has now issued a response (you can read the full statement below) and claims that when the Model S tested by LTA left Tesla’s factory in 2014 (yes it took a while to import it), it had an energy consumption rated at 181 Wh/km, less than half of what Singapore’s transport agency is claiming. How can we account for the discrepancy? 

LTA confirmed that if it would have used 181 Wh/km instead of 444 Wh/km in its CO2 emissions calculations, the Model S would have qualified for an incentive rather than a fine.

CO2 emissions for a Model S powered by Singapore’s electric grid:

  • Based on Tesla’s 181 Wh/km = 90 g CO2/km
  • Based on LTA’s 444 Wh/km = 222 g CO2/km

It is the difference between the Model S polluting less than half as much as a Mercedes S-Class in the case of Tesla’s calculations, and more than the gas-powered S-Class in the case of the LTA’s calculations.

Now how the LTA came up with that number is still not clear, though the agency says it using the United Nations Economic Commission for Europe (UNECE) R101 standards. Tesla says they are having “cooperative discussions” with the LTA to ensure they correctly testing the Model S.

With such a big difference, it’s difficult to image what happened to the Model S to be rated at 444 Wh/km. Cranked A/C? Heavy right foot? Some are even suggesting that it could be as simple as an error while converting from miles to kilometers:

[tweet align=’center’]

Could a simple mathematical error have caused this situation?

Here’s the full statement Tesla sent us:

The Model S that our customer imported into Singapore left our factory in 2014 with energy consumption rated at 181 Wh/km. As the Land Transport Authority has confirmed, this qualifies as the cleanest possible category of car in Singapore and entitles the owner to an incentive rather than a fine.

Model S achieves this result because CO2 emissions in gas-powered cars are far higher than in electric cars. In Singapore, electricity generation releases roughly 0.5kgCO2/kWh. Based on energy consumption in Model S of 181 Wh/km, this results in 90 g CO2/km. Driving an equivalent gas-powered car like the Mercedes S-Class S 500 results in emissions of approximately 200 gCO2/km. And because of oil extraction, distribution, and refining, approximately 25% more has to be added on top of that to calculate the real carbon footprint of gas-powered cars. That means an electric car like the Model S has almost three times lower CO2 per km than an equivalent gas-powered car. Moreover, as Singapore increases the percentage of grid power from solar and wind, the CO2 from electricity drops with each passing year. 

We are having cooperative discussions with the LTA to ensure a proper understanding of these issues and to make sure that they are correctly testing our customer’s Model S. Based on the positive nature of those discussions, we are confident that this situation will be resolved soon.

Until the issue is resolved, it is likely that Joe Nguyen’s Model S, the one used in LTA’s tests, will be the only Tesla on Singapore’s roads:

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