Linfairn Wind Farm Addendum Appendix A1.1: Carbon Balance

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1 Appendix A1.1: Carbon Balance Assessment 1.1 Introduction A carbon balance assessment was undertaken for the Project to estimate the carbon dioxide (CO 2 ) emissions that will be avoided by generating electricity using WTGs rather than non-renewable forms of electricity generation, offset against the estimated loss of CO 2 from the site due to peat disturbance, and the carbon cost of the manufacture and transport of the required infrastructure. The carbon calculator version (Scottish Government, 2012) was used and was the most recent version at the time of the application. SEPA reviewed this carbon balance assessment and comments were provided in their consultation response dated 19 October SEPA note that for the majority of comments that the carbon payback period is unlikely to change significantly as a result of their recommended changes. The following text includes a summary of SEPA s comments and our responses, which may be in the form of clarification or justification of the assumptions used in the carbon balance calculator, or a description of changes made to address the comment (section 1.2). The carbon balance assessment has been updated for the revised Project using the carbon calculator version (Scottish Government, 2014) and this is summarised in section 1.3 and within addendum Chapter A SEPA Review This section summarises SEPA s comments on the carbon balance assessment included in the ES and provides clarifications to these comments or changes to the assumptions where made Peat Depth The same maximum and minimum and expected values have been provided for peat depth at turbine foundations, hardstandings and access tracks. Given the variability of peat depths on site shown in Appendix 9.2 of the Environmental Statement (ES) a range of peat depth values is expected. In addition, no information has been provided on how the average peat depths have been calculated. 14/7048/001/GLA/O/R/001 Revision B1 Page 1 of 8

2 Peat deposits at the site are located as discrete pockets, where depth ranges from m. For both the original Project and the revised Project, the majority of the infrastructure has been sited to avoid peat deposits. For the revised Project, only five of the 17 WTGs and hardstandings and 2.5km of the 13km of access track are located on peat deposits. There is no provision in the calculator to take this variation into account, e.g. an average value for peat depth at all turbine locations is required. Volumes of excavated peat have been calculated for the outline Peat Management Plan (PMP) (see Appendix A9.3). The average peat depths entered into the calculator were therefore determined by taking the calculated volume of peat for each type of infrastructure i.e. WTGs, hardstandings, tracks, cable trenches, and dividing by the area of excavation as defined by the dimensions entered into the calculator. This provides a consistent approach to determining estimated volumes of excavated peat between the carbon balance assessment and the outline PMP. The latest version of the carbon balance calculator (v2.9.0) (Scottish Government, 2014) has been used for this Addendum and this new version requires the input of an average peat depth for the application site (Carbon calculator ref: Core input data sheet/cell C25). This has been determined as 0.44m using ArcGIS spatial analysis tools for the application boundary. As noted above, the majority of the infrastructure avoids peat deposits and therefore the average depth is lower than that for the whole of site area within the application boundary. As such, the same methodology as in the previous version of the calculator has been used to estimate the average peat depths at infrastructure locations for the revised Project. The volumes of excavated peat have been defined in the updated PMP (Appendix A9.3). A worked example for WTGs is as follows: Calculated volume of excavated peat in PMP = 1,212m 3. Carbon calculator assumes rectangular foundations = 18m x 18m x 17 WTGs. 1,212 / (18*18*17) = 0.22m as the average peat depth. Minimum and maximum peat depths have been estimated by varying the average peat depth by 10%. 14/7048/001/GLA/O/R/001 Revision B1 Page 2 of 8

3 1.2.2 Volume of Concrete No data on the total volume of concrete use has been reported in the Construction Input Data sheet under volume of concrete used. The Construction Input Data sheet is not used in this case, as the dimensions of the WTG foundations and hardstandings are the same throughout the development i.e. Carbon calculator ref: Core input data sheet/cell C48 option to enter detailed information is not selected. The emissions due to WTG life are calculated with respect to WTG capacity based on the equations included within the calculator (as described in Appendix A1.2, tab 2: CO 2 loss due to WTG life). None made Dry Bulk Density and Carbon Content of Dry Peat The average dry bulk density value of 0.1 g/cm 3, identified in Page 6 of Appendix 9.2 of the ES, from the samples taken on site should be used instead of Scottish generic values provided. According to Page 6 of Appendix 9.2 of the ES, based on the peat samples taken on site, the Total Organic Content of the peat ranged between 49-55%. However, Scottish generic values have been input in the carbon calculator. When available, the input of site values in the carbon calculator is recommended. Previous feedback from SEPA indicated that it was acceptable to use Scottish average values for dry bulk density and carbon content of peat, and that it was preferable to continue to take on-site samples for comparison with the national data. This was the approach taken in the carbon balance assessment. SEPA s recommendations have been applied. The expected values for dry bulk density and carbon content of dry peat in the revised carbon balance are based on the samples taken on site. The Scottish average data has been retained for the minimum and maximum values due to the higher uncertainty in the site-specific data due to the small number of samples (6 for carbon content, 9 for dry bulk density). 14/7048/001/GLA/O/R/001 Revision B1 Page 3 of 8

4 Table 1: Comparison between Scottish National Data & Site-specific Sample Data Parameter Scottish National Data Site-specific Sample Data Average dry bulk density (g cm -3 ) Average carbon content (%) Access Tracks Section of the ES identifies that 13.3 km of new access tracks is proposed. However, 15.9 km of additional access tracks have been reported in the carbon calculator. Revision or further justification of the access track length values included in the carbon calculator is required. This appears to be an error in section of the ES. The carbon balance assessment has been updated with the revised layout and therefore these values have changed. There will be 13km of access track required for the Project Cable Trenches Page 4, Appendix 9.3 of the ES identifies that 3,018m 3 of peat will be excavated for cable trenches. However, according to the information input in the carbon calculator, cable trenches will follow access tracks therefore, no additional peat will be excavated for cable trenches. Clarification/amendment of the figures for cable trenches provided in the carbon calculator is required. Clarification: The cable trenches will follow the access tracks, however a separate trench for the cable will require excavation. disturbance of the peat may occur during the construction of the access tracks however it is considered more appropriate to take a conservative approach for the carbon balance assessment and Peat Management Plan (PMP) by including the cable trenches as a separate item. 14/7048/001/GLA/O/R/001 Revision B1 Page 4 of 8

5 The average peat depth cut for the cable trenches has been updated in line with the approach described in section as only ~2.5km of the cable trench passes through peat deposits Average Water Table Depth Expected water table depth is given as 0.3 m, the same as maximum value provided. This is much lower than would normally be anticipated for intact peat soils, which is around 0.1 m. 0.3 m may be a reasonable water table depth in eroded or extensively drained peat, but there is no evidence in the information presented in the environmental statement or elsewhere that suggests that the peat is not in good condition. The value entered for water table depth should be either change to (minimum = 0.05 m, expected = 0.1 m, maximum = 0.3 m for peat in good condition) or evidence of peat degradation (e.g. drainage or erosion) at the development site should be provided, particularly around planned infrastructure locations. It may be necessary to perform suitable measurements of water table depth across the site, in which case a suitable number of measurements (at least 10, corresponding to predicted infrastructure locations) should be made, and the experimental methodology used and any calculations made should be outlined fully. As noted in the original submission, the average water table depth is based on reporting by Allot et al (2009) as referenced within the calculator whereby intact sites have water tables close to the surface (<0.1m) whilst eroded sites had an average water table >0.3m below the surface. The habitat assessment (Appendix 7.1 of the ES) described modifications to the bog habitats at the site arising from drainage, grazing and poaching and a number of areas of peat erosion were noted in the Peat Landslide Risk Assessment (PLRA) (Appendix 9.2 of the ES) and drains mapped on Figure 9.7 (Volume 3 of the ES). There is evidence of peat degradation at the site, and furthermore the infrastructure has been sited away from deeper, more extensive peat deposits. Reducing the expected value for average water table depth from 0.3m to 0.1m as recommended by SEPA reduces the payback period by 0.2 years. The original values have therefore been retained as this provides a more conservative approach. 14/7048/001/GLA/O/R/001 Revision B1 Page 5 of 8

6 1.2.7 Average Rate of Carbon Sequestration in Timber Further information on the tree species to be felled and their yield class needs to be provided in order to justify the average rate of carbon sequestration in timber input in the carbon calculator. In addition, further information on the species to be planted as part of the compensatory planting is required. Clarification: The average rate of carbon sequestration in timber is dependent on the species and yield class. The plantation at the site consists of spruce (Picea species) however the yield class has not been determined. The value used in the carbon balance calculator (3.6tC ha -1 yr -1 ) is based on yield class 16 as assumed in SNH technical guidance (referenced in the calculator). As the yield class at the site is unknown, the minimum and maximum values have been updated to reflect the average carbon sequestration for a range of yield classes (class 6 24) for spruce species ( tC ha -1 yr -1 ) 1. Felling of the plantation is occurring only where infrastructure is proposed i.e. the access track, and no clear felling is proposed. The area felled has been updated to reflect the revised Project and uses a conservative assumption that a 50m buffer either side of the access track will require felling Best Practice It is requested that proposals are included to treat and restore any gullying which occurs on site as a result of altered hydrological flow paths due to construction. In areas where commercial forestry has been felled, it is requested that peat bog restoration is considered where possible. 1 Dewar, R.C. and Cannell, M.G.R Carbon sequestration in the trees, products and soils of forest plantations: an analysis using UK examples. Tree Physiology 11, /7048/001/GLA/O/R/001 Revision B1 Page 6 of 8

7 Clarification: The approach taken in the carbon balance assessment was to assume that no restoration is undertaken in order to provide a conservative estimate of the payback period. Chapter 9 of the ES outlines mitigation measures and best practice approaches to minimise the risk of soil erosion during construction. Peat bog restoration has not been considered in areas to be felled. Felling is only proposed where infrastructure is located (i.e. no clear felling) and peat deposits in this area are localised, small in extent and less than 1m deep. It has now been assumed that gullies formed due to the Project will be blocked. 1.3 Carbon Balance Assessment for the Revised Project The carbon balance assessment has been updated for the revised Project and incorporates the updates listed in section 1.2. Version of the carbon balance calculator has been used (Scottish Government, 2014) which is the most recent version at the time of submission. The assumptions used in the assessment, not included in section 1.2 above, are as follows: The expected capacity factor of 26.06% has been calculated by RenewablesUK based on the average capacity factor for onshore wind in the UK over the past five years, as published by DECC 2. The maximum capacity factor is taken as the Scotland average This is unchanged from the original application. The mean annual temperature ( ) from the Met Office regional mapped 1km-grid point data set has been used to represent the average air temperature. This is unchanged from the original application. The range of extent of drainage around drainage features at the site is based on the values from the literature presented in Nayak et al (2008). An average extent of 15m is considered to be a conservative assumption due to the typically low hydraulic conductivity of peat. This is unchanged from the original application. 10 years for the regeneration of bog plants after restoration is a conservative assumption. This is unchanged from the original application. 2 Department of Energy & Climate Change (2013) Digest of United Kingdom Energy Statistics /7048/001/GLA/O/R/001 Revision B1 Page 7 of 8

8 The counterfactual emission factors have been updated based on those published in the Digest of UK Energy Statistics (DUKES) as recommended for version of the carbon balance calculator 3. Table 2 shows the calculated carbon losses and savings and the estimated payback period over the operational period of the wind farm. The detailed calculation sheets of the potential carbon losses and savings of the proposed Project are included in the carbon calculator which is provided with this addendum. The estimated payback period for the revised Project is 3.0 years compared to grid mix electricity generation (range years). In comparison to fossil fuel mix and coal fired electricity generation the payback periods of the Project reduces to 2.1 years (range years) and 1.5 years (range years) respectively. Table 2: Linfairn Wind Farm Revised Layout Carbon Balance and Payback Period CO 2 Balance (over 25 year operation period) (tco 2 )* Grid mix Fossil fuel mix Coal-fired Emissions savings 1,337,063 1,887,436 2,674,127 Emissions losses (carbon fixing potential, peat removal, drained peat, organic carbon leaching, backup power generation, WTG production, transport and decommissioning) 162, , ,205 Carbon savings 1,174,858 1,725,230 2,511,921 Payback period (years) * based on expected values /7048/001/GLA/O/R/001 Revision B1 Page 8 of 8