Scottish Government

Appendix 12 SUMMARY OF DATA SOURCES AND METHODS

Scotland's energy consumption and related CO ₂ emissions have been assessed for 2002. Scotland consumed 1,74.5 TWh (628 PJ) of delivered energy, emitting 45.1 Mt of CO ₂ (12.3 Mt as C). Using a ratio of primary energy: delivered energy of 2.60:1 for electricity and 1.0:1 for fossil fuels, the total primary energy consumed would be 221.5 TWh. Scotland generated a further 8.0 TWh of electricity, which was exported to England and NI⁸⁵.

It is proposed that these figures are used for the Scottish Energy Study 'declared' energy and CO ₂ emissions for the selected BY of 2002. However, their use should always be accompanied by a caveat with some description of how they have been derived, namely:

• Direct energy consumption and associated CO ₂ emissions were calculated from a top-down assessment of fuel consumption in Scotland, cross-checked with a bottom-up assessment of total fuel consumption and fuel split by energy demand sectors.
• CO ₂ emissions from electricity were calculated by applying standard UK average CO ₂/kWh factor to the quantity of 'useful' electricity consumed within Scotland, i.e. after exports to England and NI had been discounted ⁸⁶.
• CO ₂ emissions (and primary energy losses) from oil refineries were attributed to the refineries, rather than attempting to apportion the energy to the refined petrol, diesel and fuel-oil. In this aspect, refineries have been dealt with in a similar manner to 'Industry' rather than 'electricity'. It is believed that oil refining and electricity generation are sufficiently dissimilar to warrant this differentiation, plus this approach eliminates the need to add 5-10% to all DUKES standard emission factors for refined fuels.
• Process CO ₂ was taken from the NAEI estimation for Scotland, with some cross-checking with knowledge of industry.
• For land-use change, the CO ₂ emissions from soil and carbon sink data were taken from the NAEI estimation for Scotland. The NAEI figures have been used as they are, although it may be that tree growth should only be considered a temporary carbon sink and the real, long-term impact from forest growth may need to be reviewed.

Data sources & methods

Energy and CO ₂

The study used two parallel approaches to the gathering and analysis of data:

• 'Bottom-up' energy demand and fuel split data, for the domestic, industry, services and transport sectors, were gathered and compared with…
• 'Top-down' figures for solid, oil-based, natural gas, renewable and nuclear energy, plus electricity.

Energy flow patterns can be effectively represented in Sankey flow diagrams. A 'skeleton' version for Scotland 2002 (together with three drill-down detailed versions) has been presented in section 6. For this, the electricity TWh and its associated CO ₂ emissions have been derived by multiplying the electricity consumed within Scotland by a standard UKCO ₂ emission factor. This is detailed in section 8.

Where possible, bottom-up and top-down totals were compared and contrasted for all fuels, including consumption for electricity generation. For this study, all came to within +/- 3% of each other (and in many instances within +/- 1%), which gave confidence to the figures used. Based on this, the summary figures from the Scottish Energy Study were:

Table A12.1: Summary of energy figures for Scottish Energy Study - based on top-down

The corresponding bottom-up version of this gave:

Table A12.2: Energy consumption, based on sum of demand sectors in Scotland - 2002

The two totals are within 1% of each other.

Overall, Scotland accounts for slightly greater energy consumption than pro-rata its population, 9.1% compared with 8.5% of the population. The main reasons are the requirement for extra heating in domestic and services, plus greater than pro-rata oil refining, which more than offset the slightly below pro-rata consumption by industry and transport. The fuel split is not dissimilar to the UK average, with slightly lower demand for coal, but higher consumption of gas and electricity.

Production of electricity consumes primary energy sources to provide higher value (and more versatile) secondary fuel, which in turn is consumed within Scotland and exported to England/ NI. Estimating electricity supply and consumption, in particular, accounting for exports, losses and storage (via pumped hydro), proved one of the more difficult aspects of this study. It is recommended that this topic be given more attention. A fair and robust model should be developed for assessing electricity and attribution CO ₂ emissions to its generation/ consumption, for both the BY and future projections. It is recommended that a model that is appropriate for Scotland be developed in partnership with the Scottish Executive.

Non-energy and process CO ₂

The headline figures for 2002 are shown below:

Table A12.3: Scottish non-energy CO ₂ emissions

Scottish soils emitted some 5.0 Mt of CO ₂ in 2002, much comes from disturbances to the peaty soil in Scotland.

The overall contribution is a net sink if one credits the 9.9 Mt of CO ₂ absorbed by forest growth. However, this raises a CO ₂ accounting point: unless the carbon is permanently sequestered, it will eventually work its way back into the carbon cycle. Without some form of assurance over this, it is debatable if the benefits from forest growth should be included in an assessment of CO ₂ emissions.

Fugitive emissions from oil, gas and industry processing (cement, glass and primary aluminium) were nearly 1,600 kt of CO ₂ in 2002.

Robustness of Base Year in relation to adjacent years

Finally, one of the primary purposes for assessing the energy 'footprint' for Scotland is to benchmark a reasonable start year, produce overall consumption and emission figures and, based on these, project realistic but challenging reduction targets by 2010, 2020 and beyond.

A brief analysis of CO ₂ emissions for 2000, 2001 and 2002 showed that there were some differences in energy and process-related CO ₂ emissions between the years. The 2000 and 2001 totals were similar, but 2002 was approximately 3 Mt less than 2001.

Part of this reduction will be real and part is likely to be due to the reporting methodology. Changes to the electricity generating fuel mix and overall efficiency brought about by increased use of renewable energy and CCGT, plus modest improvements to direct energy consumption by industry and services, are likely to represent real reductions which will be sustained in coming years. However, 'exaggerations' in the NAEI Report, such as changes in electricity exports, or quirks in reporting transport fuel, would not be real and should be discounted.

Overall, 2002 appears a reasonable BY to use, although it must be noted that CO ₂ emissions for this year are 3 Mt (or 6%) lower than the two preceding years. This needs to be taken into consideration if and when medium and long-term energy and CO ₂ saving targets are set.