Yes, you're right. Maryland actually has more people than Denmark. Maryland gets a lot of power from nuclear, though (Calvert Cliffs).

This Danish goal, getting rid of coal plants by 2025, may not be hard to achieve, as they can import electricity, using sub-sea HVDC, from Norway, which has plenty of hydro, or by importing it from Sweden, which has plenty of nuclear and hydro. Running all of the country on wind power is a mirage. Where does the power come from when the wind doesn't blow, which may happen from time to time ?

It is true that the GDP per capita is higher in the USA than in most EU countries, but I think you should also point out that Americans, on average, work more hours than Europeans. I don't have the exact numbers at hand (they can be found on the OECD site), but if i recall correctly, the hours worked per capita is much higher in the USA than in e.g. France or Germany. If you translate the hours worked per capita into working weeks, Americans work on average 4 or 5 weeks more than the French and the Germans (they apparently prefer long vacations). Labour productivity per hour worked is not necessarily worse in France or Germany than in the US of A.