IF the government happens to choose the right technology to subsidize, then a subsidy is efficient. Suppose they pump a lot of money into wind, and then someone

IF the government happens to choose the right technology to subsidize, then a subsidy is efficient. Suppose they pump a lot of money into wind, and then someone discovers a solar solution that's cheaper. That giant investment will have been wasted. By contrast, a tax lets researchers competing on a level playing field find the right substitute.