Forthbank Wind Energy Development - Partnerships for Renewables

Forthbank Wind Energy Development
losses and gains during the construction and operation of the proposed wind energy
development need to be evaluated on a site specific basis.
6.4.12 Protecting and retaining the substantial reserves of carbon held in Scottish soils is an issue
recognised by the Scottish Government. Scottish Natural Heritage (SNH) produced a
Technical Guidance Note in 2003 for calculating carbon ‘payback’ times for wind farms. Nayak
et al. updated this guidance in 2008 6 and 2009 and devised a carbon balance tool for wind
farms being constructed on peat and which considers the impacts of wind farms during
construction and operation on soil stability and long-term greenhouse gas emissions. Although
the proposed wind energy development is not located on peat, the calculator can be used to
give an indication of the amount of carbon emitted through the lifetime of the site, including
from the construction and operation (maintenance, etc) of the wind turbines.
6.4.13 The tool by Nayak was used to calculate the carbon balance (sum of the carbon losses and
gains) for the proposed wind energy development. However, some amendments were made
to the calculator to reflect the fact that disturbance would be to primarily mineral soil rather than
peatland – therefore the risk of carbon loss from draining the soils is avoided, which is a major
factor increasing payback time on peatlands 10 . The benefit of the calculator is that it allows for
the payback time to be calculated including the carbon involved in the construction and
erection of the turbines (steel construction, transport, concrete in foundations and hardstanding
etc) reflecting that the carbon “benefit” of the project is not immediate – though the payback
time is shorter than on a peaty site.
6.4.14 Table 6.1 shows the calculated carbon payback time associated with the proposed wind
energy development. A breakdown of the input values and total carbon losses and gains
associated with the proposed wind energy development are shown in Appendix 6.1.
Table 6.1 Proposed Wind Energy Development Carbon Balance and Payback
Carbon Gains (t CO 2 eq) Carbon Losses (t CO 2 eq) Overall Carbon Balance
(t CO 2 eq)
Total Payback Time
(months)**
0 * 8638 8638 6
*There will be no improvement of degraded bogs, felled forestry or restoration of peat from borrow pits.
**The carbon payback time of the proposed wind energy development is calculated by comparing the loss of carbon
from the site due to wind farm construction with the carbon savings achieved by the wind farm (against fossil fuel
counterfactual) during a 25 year operating period.
6.4.15 The estimated total carbon payback time of the proposed wind energy development, based on
carbon losses and gains compared with fossil fuel generation, is 6 months. This is increased to
9 months against the current mix of electricity generation, which includes other renewable
electricity sources and the payback is decreased to 5 months compared with coal-fired
electricity generation. It should be noted that although the CO 2 emitted during wind farm
construction is taken into account in this calculation, that produced from construction of the
other forms of power stations is not – therefore, in some ways this calculation is biased against
the wind generation.
6.4.16 Therefore, when considering the 25 year operational period of the proposed wind energy
development, the CO 2 payback time is very short in comparison.
6.4.17 It should be noted that these figures have been calculated based on "reasonable worst-case"
assumptions in the absence of site specific information, and the results are therefore likely to
be conservative.
November 2010 Chapter 6 Page 5
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