I left a comment on a green jobs post the day after pagan celebration of a Christian holy day:
That is why economics is known as the dismal science. We strange economists are most adept at recognizing the opportunity costs of various decisions. No one else really seems to care if opportunity costs offset some, or all, of the benefits of a good idea.
Opportunity cost is a strange notion to some (especially intro micro students) ... it is the value of the next best alternative whenever a choice is made. For example, if I purchase a $1000 flat panel LCD TV, the true cost of the TV is not $1000, but what I could purchase instead (such as $500 in each kid's college education 529 plan [sorry kids]).
In the case of green energy subsidies, if you are an economist then you must at least wonder if this is the best way to spend the money. There are benefits of pushing down the costs of green energy (e.g., improved air quality), and there are opportunity costs. Ignoring the opportunity costs is likely to lead to wasteful spending. Considering the opportunity costs is likely to lead to better social decision making -- regardless of whether the benefits of the subsidies exceed the costs.
The notion of opportunity cost, its recognition and the inevitable result that not all great sounding ideas are really great ideas, is the most important thing that economists bring to many policy discussions. Pointing out the unpleasantantries of opportunity cost is one of the purposes of this blog. The dismal part of the dismal science can not be avoided.