Opponents of fracking in the UK regularly claim we don't need it because we've got "clean" energy sources like wind power that we can rely on instead.
As we've pointed out here previously, it's not a question of shale gas OR renewables, it's about what shale gas AND renewables can accomplish together - remembering that wind and solar only supply electricity whereas gas is much more versatile and can also provide heat and be used as feedstock in a variety of chemical manufacturing applications.
But putting all that aside, is wind really as "clean" and "green" as they say?
For a start, building wind turbines relies on the extraction and processing of minerals and metals - which all consume lots of energy and are responsible for a significant release of CO2 emissions.
Take steel as an example. According to the steel industry itself, producing 1 tonne of steel gives rise to two tonnes of CO2. Wind turbine towers are made from steel. Here's how much the towers of three popular wind turbines weigh and what their respective "embodied CO2" looks like:
General Electric GE 1.5
Tower weight 71 tonnes
Embodied CO2 = 142 tonnes
Tower weight 152 tonnes
Embodied CO2 = 302 tonnes
Tower weight 220 tonnes
Embodied CO2 = 440 tonnes
Then consider the concrete foundations. Concrete consists of limestone aggregate mixed with sand, cement and water. Cement manufacture is another very CO2-intensive process. The foundations for wind turbines vary according to size, weight and location but typically range from 300 to 1,000 tonnes. The embodied CO2 per tonne of typical reinforced concrete is 0.115 tonnes of CO2 per tonne. Therefore the range will be somewhere between 34.5 and 115 tonnes of CO2 per wind turbine foundation.
According to Renewable UK, the wind industry trade body, there are 6,410 onshore wind turbines in the UK. Assuming that they're all the smaller GE 1.5 model on a 300 tonne foundation, the embodied CO2 of these wind turbines would be 1,820,440 tonnes in the steel towers and a further 221,145 tonnes in the reinforced concrete, bringing the total to 2,041,585 tonnes of CO2 (318.5 tonnes of CO2 per wind turbine).
And that's before you take into account the issue of digging-up soil for turbine foundations, which will release some stored CO2 and also biogenic methane - a problem that's exacerbated where wind turbines are installed in peat soil on moorland hilltops. Add the petrochemicals used to make turbine blades, and the rare earth metals like neodymium used to make lightweight magnets, and suddenly a wind turbine looks anything but "clean" - especially considering that the trend is towards bigger and bigger wind turbines.
If we wanted to try and obtain 100% of our electricity using the GE 1.5 variant, we'd need to generate 330,000,000 MWh a year. A single GE 1.5 can be expected to generate 3,942 MWh a year (capacity (MW) x capacity factor (0.30) x hours per annum (8,760)) and so we'd need 83,713 wind turbines - or 77,303 more than we have already.
At 318.5 tonnes of CO2 per turbine, that would add up to 24,621,005 tonnes of CO2. Worse still, turbines only have about a 20 year life expectancy and so you'd be constantly adding to this carbon footprint.
What people obviously mean when they say that wind energy is "clean" energy is that wind turbines don't produce CO2 emissions when generating electricity, unlike burning coal, oil or gas do. We agree with that, and we agree that we must accept the embodied CO2 emissions of wind turbine construction as a necessary evil in the pursuit of lower and low-carbon power.
But what we can't agree with is the "clean" label being applied to wind energy by anti-frackers to try portray shale gas as "dirty". Anyone doing this is either oblivious to the facts about how wind turbines are made and installed, or they're being dishonest.