Mistakes by Berkeley, the University of California

At the end of November 2009, a document emanating from Berkeley, "Economic and environmental evaluation of compressed-air cars" was published on the internet (www.iop.org/).

This document claimed to establish scientifically that MDI compressed-air vehicles are more expensive and more polluting than a petrol or electric car. The comparison made is with Smart Fortwo petrol and electric cars. The technical facts used to arrive at these conclusions are grossly incorrect or falsified.

The vehicles compared cannot in fact be compared.

First of all, the classifications "normal car" and "light car" make no sense at all in this document as it introduces for comparison a 300 kg potential electric vehicle which in reality does not exist.

The Smart petrol weighs 837 kg, the Smart electric weighs 924 kg; the MDI Airpod weighs 330 kg (with driver).

Other MDI vehicles which could be compared with a Smart (the Air Mini and AirOne/Oneflowair for example) will be equipped with the bi-energy (and not hybrid) technology that the authors of the Berkeley report themselves consider to be competitive (last sentence of the résumé).

Energy values distorted to the benefit of the Smart

Many of the values used in this document (3.1 on page 3 and table 1) aim to falsely increase the energy efficiency of the Smart Fortwo. Thus:

1/ A consumption of 5.2 l/100km and an efficiency of 21.2%. With a consumption of 5.2 l/100km, the efficiency of the Smart would be set at only 15.5% and not 21.2% as shown.

2 / What’s more, in contradiction in the same document (figure 3 page 5), an exact value of 225 MJ for 100 km (2.25 MJ/km in the text) is shown, which represents a consumption of 7.5 l/100km (rather than 5.2 l/100km). This figure of 7.5 l/100km, an actual consumption figure, was confirmed by the French Auto Plus car review of 7 April 2009. The efficiency of the Smart is thus 10.6%, half the value shown in this document as the basis of a comparison.

Every engineer and scientist involved with cars knows very well that the efficiency value for a petrol car in the urban cycle lies somewhere between 9% and 13% :

• An OCDE document shows, page 378, efficiency values for a petrol engine in the urban cycle between 9 and 11% :

  Towards Clean Transport - Fuel Efficient and Clean Motor Vehicles

• A document published by PriceWaterhouseCoopers, entitled "The Automotive Industry and Climate Change", refers to a US Environmental Protection Agency (EPA) source which, on page 67 gives an efficiency of 12.6%:

http://www.pwc.fr/the_automotive_industry_and_climate_change.html

3/ In addition, 225 MJ/100km (figure 3) represents 178.5 g CO2/km rather than 125 g CO2 emitted per km, as shown.

Values distorted to the detriment of the MDI Airpod

1/ Transmission efficiency

An efficiency loss of 29% in the transmission is shown, namely a result of 71% efficiency, forgetting to also apply this loss to the Smart electric, although this uses a transmission similar to that of the MDI vehicle.

The reference chosen by the authors is a 2001 3-litre Ford Taurus with a 4-speed automatic transmission, which has nothing to do with a car intended for an urban environment.

The EPA document already mentioned shows more correctly a transmission loss of 5.6%, namely an efficiency of 94.4%. MDI uses simplified transmissions with efficiencies higher than 95%, keeping the figure at 95% efficiency in its documents.

2/ Effective in-town efficiency taking vehicle weight into consideration

To implement the EEC urban cycle, taking into account differences in mass, the energy requirement of the MDI Airpod is 0.56 kWh. To go through the same cycle, the Smart electric requires 1.4 kWh. The practical efficiency in town, included in "Table 1 corrected" of the report, allows direct comparison of the requirements in use, therefore the primary energy requirement necessary to implement the urban cycle whatever the primary energy supply and/or electricity (coal or other):

The authors have also completely neglected the fact that MDI cars can take up their energy supply from a service station in less than 2 minutes and that the compressed air at these stations can come directly from renewable energy such as wind or water. In which case the GHG (greenhouse gas) emission in gCO2 is zero.

Quite obviously all these fundamental errors completely distort all the results, comments and conclusions of the Berkeley report as far as the impacts (environmental (pollution) and economic (usage price)) of compressed-air vehicles are concerned.

3/ Compressor: price

The compressor, inboard in our whole range, except for the Airpod where it will be outboard but supplied with the car, costs 350/400 €, a value which is an integral part of the vehicle sale price.

The price of the production Airpod is between 6,000 and 7,000 € (tank and compressor included).

4/ MDI tank and batteries: price and life duration

The tank on the MDI vehicle is fabricated in micro-production factories and included in the price of the vehicle; the tank is costed at 1,200 €.

These tanks have a life of 12,000 discharge cycles, which means, for 3 to 400 cycles per year, a life of about 30 years. The batteries have a life of only 1,000 discharge cycles, namely one twelfth as long.

The current price of the batteries is of the order of 1,000 € per onboard kWh which, for the reference electric Smart represents 13,000 € for a life of only 1,000 cycles. After 3 to 5 years, a replacement battery pack is therefore necessary, namely a new outlay of 13,000 €.

Conclusions

These fundamental, unscientific mistakes turn this document into something which deceives the public and is unfair competition, to the advantage of those who have no interest in seeing MDI succeed in its efforts. After correction of the facts, MDI vehicles in use can be seen to be in a better position than Smart petrol and electric as far as the environmental effects, running costs and decidedly lower acquisition cost are concerned.

MDI will take all necessary steps to obtain rectification and damages for any harm which may result.