How expensive and why? In this case it sounds like someone was charging a city government a premium for social and political reasons. Electricity is just like any other commodity and people try to get as much as they can for it. Marketing it as Green CAN SOMETIMES earn a premium but usually not.
It was expensive because it was wind-generated.
Currently, wind-generated electricity is added to the grid as a social service, rather than an economic necessity.
Austin bought the wind credits, thinking everybody was as illogical as the city council, and hoping that they would pony up for the increased rates.
Electricity is only a commodity AFTER it’s added to the grid.
Before that, it’s an economic entity and now, apparently, a political/social one as well.
Their version:
http://www.ci.austin.tx.us/greenchoice/
The truth:
http://www.statesman.com/news/content/news/stories/local/2009/07/12/0712greenchoice.html