The carbon payback times for wind turbines are much shorter than previously thought, according to international research carried out at the largest community wind farm in the UK. German student, Katharina Lutz, found the turbines at Beinn Ghrideag had a payback time of just 47 days – a drastic reduction on the previous, widely accepted, estimate of 2.3 years.
Point and Sandwick Trust’s community-owned wind farm at Beinn Ghrideag. University research finds this wind farm had a carbon payback time of just 47 days – a drastic reduction on the previous estimate of 2.3 years. (Photo: Sandie Maciver of SandiePhotos)
‘Carbon payback’ is a term referring to the length of time it takes for the negative environmental impact from the construction of a wind farm on peatland to be offset by the positive environmental impact of generating clean energy instead of burning fossil fuel. When peat is disturbed for large concrete foundations to be laid for turbines, greenhouse gases are released into the atmosphere.
Lutz carried out her research at Beinn Ghrideag near Stornoway in the Autumn, with the academic support of mentor Alasdair MacLeod from Lews Castle College UHI and financial support from community wind farm owner Point and Sandwick Trust.
According to her report, entitled “CO₂ Emissions from Wind Turbines on Peatland: A Practical Calculation”: “Estimates for the payback time for turbines on peatland have been quoted as 2.3 years (Pearce, 2009). This is based to an extent on an influential report by Nayak and collaborators at the University of Aberdeen who developed a carbon dioxide calculator, variations of which are still used to estimate the impact of a wind farm proposal (both by supporters and opponents)”.
The report further summarized: “Installing large wind turbines on peatland has the disadvantage of exposing carbon long trapped in the ground to decomposition, and some estimates suggest a turbine can take several years of operation to compensate for the associated carbon dioxide emissions.
“The main reason for these projected high carbon payback times is the assumption that all displaced peat becomes fully oxidized and that the construction not only causes drainage within the immediate construction area, but that the effect can extend outwards by a distance of up to 400 m. However, existing turbines on a wind farm on the Isle of Lewis, Scotland, on a site which is typical of the region, were found to have a carbon payback time is only 47 days when the actual impact following several years of operation is established.
“The result is based on a flora analysis and accurate peat depth and composition measurements, and references three years of electricity generation data. The calculation of CO2 displacement associated with turbine electricity production uses the fossil fuel emission factor for the United Kingdom in 2016 rather than the overall grid emission factor in order to accurately reflect the generation type displaced by the wind turbine output.”
When concrete foundations are being laid, peat is usually disposed of by being spread thinly over the surrounding area, with the assumption that all the displaced carbon will end up as atmospheric carbon dioxide. However, Lutz found that less drainage takes place than had been thought – and that extensive drainage is not necessary as the hole can be backfilled.
Her mentor, college lecturer Alasdair MacLeod, explained that peat was “90% water bioweight”. When wet, peatbog contains no oxygen and very few microbes, “so the carbon in it is protected” from degradation. However, “once you drain it, you expose it to the oxygen so the microbes then have oxygen available and the peat will be metabolized”, causing CO2 to be released.
He stressed the “huge assumption everybody makes” was that it was necessary, in order to create a hole in the ground for a wind turbine, to remove all the peat, then put in the hard standing, and have drained all round, to a distance of perhaps 100 meters. “So not only are you oxidizing the peat you removed, but you’re also drying out a massive area round it”.
“What Katharina found was that when you need a wind turbine, you’re making a hole in the ground (but) you’re not really draining what’s around. You only need the hole open long enough to backfill it. In addition to that, what was in the hole was spread very thinly around the surrounding area and that slowly works its way back into the bog, so the peat that was originally there didn’t have a chance to dry out and just worked its way back into the bog.”
Alasdair, a senior lecturer in energy engineering, was full of praise for his “meticulous” student.
“She was very, very good. Very diligent, scientific. No assumptions made – everything had to be supported. She was a very good researcher and she had good expertise in the biological side of the project which is the moorland, flora, fauna, species and so further. I helped with the technical and scientific side – the energy side – and she learned a lot from that too. I taught her how to calculate the energy value in peat and the implications, such as how fast it grows.”
Community wind farm developer Calum MacDonald, who developed Beinn Ghrideag for Point and Sandwick Trust, said: “This is a hugely important piece of research, especially for wind farm projects in the Highlands and Islands. There is mounting evidence that the climatic conditions we have means that peat disturbance is not so great and peat recovery is generally faster in the Highlands and Islands than elsewhere in the UK and Europe.
“It’s great to have proper scientific input into an area that has hitherto been almost by rule of thumb.
“We are very proud of the reclamation we did at Beinn Ghrideag and we think it’s an exemplary model for the industry to follow.
“Community-owned projects, of course, will always be more conscientious and environmentally-minded because it’s our land and our future that we are working on.”
Beinn Ghrideag consists of three turbines, each generating 3 MW, making it the largest community-owned wind farm in the UK in terms of output. It has won several awards from the renewables, charity and social enterprise sectors, including being named Best Community Project at the Scottish Green Energy Awards in 2015.
Alasdair MacLeod said the research indicated “many turbines could be installed in Lewis without any significant effect on the peat environment”.
He added: “If you object to the turbines, you can’t object to them on the basis of what they do to the peat. Any objection has got to be something else. You may hate them because of the visual intrusion but you can’t hate them because they damage the peatland because they don’t.
“It’s significant because previous assumptions were that it always took three to five years to pay back and people said you can’t put wind turbines on peat – but you can. The reality is, when you put any wind turbines up, you don’t drain the surrounding peatland. There’s no need to drain it.”
Filed Under: Community wind, News, Projects
Tom, sorry but your calculations are way off. A 1.5MW wind turbine operating at 35% capacity factor (typical of most installations in North America in the past decade) will give 1.5MW x 35% x 7860 hours = 4599 MWh per year – this is after allowing for losses, maintenance time etc. Very different to your 51MWh – if that were true, there wouldn’t be a single turbine installed! MIT says that there is around 750 lb of rare earth minerals in a wind turbine. Most recent studies say that wind turbines will offset the CO2 generated in their production and installation in around six months.
And wind is not subsidized any more. It is now the cheapest grid scale source of power, even according to an oil industry web site https://oilprice.com/Latest-Energy-News/World-News/Wind-Solar-Are-Now-The-Cheapest-Sources-Of-Power-Generation.html
I really doubt it.
Just to let you know these are hand calcs on a napkin.
Totem contracting states that a 1.5MW turbine operating 24 hours a day for a whole year can generate 3285 MWh. That is usually at rated speed of 30-50mph winds. (Not realistic and you have to have down time for routine maintenance). They admit they usually deliver about 25% of capacity so forget the 25% for a moment. Now, for ever half of the wind speed you lose 8 times the generating capacity. So, a 40mph taken down to 20mph will get 410 MWh and a 10mph will get 51 MWh.
Columbia U has a calculation on how much energy it takes to make a ton of cement. It is 4.7M btu or 1.4 MWh. Each turbine requires 1200 tons of cement. That is from Northwest mining. So, 1200 tons of cement take 1680 MWh to produce.
Divide that by 51 MWh per year with no stops for maintenance or an unusually calm period of wind means the wind generator has to operate for 32 years to pay for the energy just for cement. That does not include mining iron ore, processing the iron ore with coal to make steel and fabrication of the steel. It does not include the 4.7 tons of copper and 3 tons of aluminum which have to go through the same processes.
Also ther are 2 tons of rare earth elements (mostly from China), zinc and molybdenum. Then you add the resins (from petrochemicals) that have to be processed and transported to the site.
Then add the end of life disposal. Many elements can be recycled but the blades cannot. Try googling wind generator blades landfill.
Even with Government subsidies, these things are decades away from breaking even. That goes with a carbon footprint as well.