5. Review of SNH Technical Guidance Document
The review of the SNH Technical Guidance Document is given in full in Appendix 1. The recommendations from the review are as follows:
- CO 2 emission from the life cycle analysis of wind turbines and the backup source should be included in the calculations of CO 2 savings and the C payback times of wind farms. This will require generic figures to be provided in guidance, although a better estimate will be obtained if specific figures are available to the developer.
- A site specific capacity factor should be used wherever practicable to provide a more realistic payback time for the site. Failing that, the best (34%) and worst case capacity factors for Scotland (27%) should be used ( e.g.DTI, 2006).
- Fossil-fuel sourced grid-mix emission factors should be updated annually.
- Calculation of C loss should include both direct loss of C from the excavated peat and indirect loss due to drainage and other site disturbance.
- A combined study on the effect of the wind farm development on the hydrology and the C cycle on peat will give a better understanding of C loss.
- The major pathways of C loss from soil is by aerobic decomposition of organic matter, resulting in CO 2 losses; anaerobic decomposition of organic matter, resulting in CH 4 losses; leaching losses of dissolved and particulate organic C associated with movement of water through the soil; and losses of C associated with erosion or the mass movement of soil. C losses associated with erosion and mass movement are highly site specific and can only be adequately estimated using dynamic simulation modelling driven by detailed site specific data. These are assumed to be negligible given adherence to Best Practice guidance. Aerobic and anaerobic decomposition losses can be estimated using IPCC defaults or more site specific relationships derived from dynamic C turnover simulations. These simulations will also provide estimates of losses as dissolved organic C.
- Simulation modelling of soil hydrology, soil erosion and C cycling could be used if sufficient information is available to provide better estimates of the extent of the area affected by the wind farm development and the impact on C losses from the soil.
- Potential effects of mitigation measures to increase C storage should be included in calculations of CO 2 savings of wind farms.
- The impacts of restoration, or after-use of wind farm sites in areas of peat or peat land should be included in appraisals of potential C loss.