evidence: "The concept of net energy must also be applied to renewable sources of energy, such as windmills and photovoltaics. A two-megawatt windmill contains 260 tonnes of steel requiring 170 tonnes of coking coal and 300 tonnes of iron ore, all mined, transported and produced by hydrocarbons. The question is: how long must a windmill generate energy before it creates more energy than it took to build it? At a good wind site, the energy payback day could be in three years or less; in a poor location, energy payback may be never. So Mr Hughes was saying only that placing windmills in bad places may mean they don’t generate enough energy to "pay back" the energy it cost to produce them, not that all turbines will fail to do so. [...] A 2010 analysis of fifty separate studies found that the average wind turbine, over the course of its operational life, generated 20 times more energy than it took to produce. This level was "favourable" in comparison to fossil fuels, nuclear and solar power.