Well, theoretically, the EU needs to cover a mere 1% of it's territory with 20% efficient solar panels, or 2% with 10% efficient panels, or 20% with 1% efficient biofuels, to replace projected energy needs for 2020 (I'm sorry I don't have a reference, this number was cited to me a by univ professor who was lecturing on the subject of solar power).

The advantage the EU has with respect to the US, is a modern grid already in place and a more frugal culture. So we only have to cover parts of southern Spain with solar panels :)

If we did a similar exercise with the USA, we have 3.5 million square miles of which we have to panel over 10,000 square miles with panels to produce all of our electricity. Maybe twice as much to produce all of our energy needs, skipping over how does the electricity propel the car. I don't doubt Europe could do it if they want to. They just have to pay three times as much for the electricity as a similar exercise in the USA.