Embodied Energy and Carbon Payback Time

One of the arguments raised against turbines – large or small – is the amount of CO2 used in their manufacture, and the length of time it takes for the turbine to save that. The wind industry has made some stabs at guessing this in relation to large turbines, and the figures are in fact very convincing. The payback time is usually less than six months, unless of course you accidentally roll half a bog down the mountain, in which case the CO2 emissions go skywards…

But for our domestic turbines, the figures are likely to be roughly as follows;

An efficient European steelworks emits about 2 tonnes of CO2 for every tonne of finished steel. Copper is almost twice that, and aluminum about six times that amount, but thankfully the weight of both these components is minor enough.

Concrete, even if no fly-ash is used in the mix varies between 173 and 436Kg Co2 per cubic meter – since we use a fairly strong mix, lets pit the worst possible scenario and go for the higher figure.

Our tower is likely to weigh about 400kg
The generator weighs a further 35kg – about 6kg of that would be copper, the rest aluminum and steel. Our foundation requires about 2.2 cubic m of concrete.

That all comes to just under 2 tonnes of CO2.

In Ireland, according to SEI, electricity comes in at 620g of CO2 per KwHr. In the UK (more nuclear) it comes in at 430g. In Ireland, the turbine, assuming a yield on a mediocre site of 500Kwhr per sq m blade area, would save 2.2 tonnes of CO2 in a year. In the UK that would be 1.5 tonnes.

So the carbon would be paid back in between a year and sixteen months, depending on whether you are in Ireland or the UK.

The turbine should have a life of at least 20 years, but the tower and base would be good for two or three times that amount. All in all, this isn’t a bad return on carbon…