What the site does say is that the idea behind the CO2 E - Race is that all of the vehicles involved must be carbon neutral. The reason for the race (and a car show) is the United Nations Global Climate Change Conference which takes place in Copenhagen next September. I expect we'll know more well before then. After all, getting the word out is part and parcel for these things, no? Thanks to Jacob for the tip!
[Source: CO2 E - Race]