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Scottish Energy Study: Volume 1: Energy in Scotland: Supply and Demand


4 Fuel Supply: Electricity and Oil

This section considers the supply of 'secondary' fuels, electricity and oil.

4.1 Electricity

This section:

  • Describes how Scotland's electricity was calculated.
  • Provides information on the current generation mix and capacity.
  • Estimates the resulting CO 2 emissions.
  • Considers how electricity supply could change in the future.

4.1.1 Approach taken to estimating Scottish electricity supply

The total electricity supply totals have been estimated from electricity generated by Scotland's three nuclear, two coal and one gas MPPs, from numerous renewable sources (predominantly hydro, some wind and thermal), plus electricity sold-on from small-scale electricity generators and CHP operators. Electricity generated by fossil-fuel CHP units that is then self-consumed by the operator is not included; instead this fuel will be 'seen' as the primary fossil fuel use within the demand sector 23. Electricity from renewable sources that is self-consumed at the point of generation (in particular, hydro-electricity at Alcan Lochaber) is included in the Scottish Energy Study figures as electricity, mainly because there is no other way of accounting for it.

Figures for 2002 were extracted from DTI 'Energy Trends' and manipulated, and are presented in Table 12.

Delivered electricity (the GWh(d) column in Table 12) was extracted from the DTI statistics. The primary energy consumption used to generate this electricity was then back-calculated (the GWh(P) column). Site-specific information is sensitive in nature and not freely available in the public domain, therefore, estimations of the generating efficiencies were made for each fuel:

  • For coal, this was estimated from 'typical' coal generator efficiencies, which can vary from less than 30% to more than 40%. Both Longannet and Cockenzie are believed to be 'typical' of UK generators and the UK average generating efficiency figure of 37%. These estimations cross-check reasonably with other estimations for Scottish coal-power generation 24.

Table 12: Primary energy and CO 2 associated with Scottish electricity generation


Gen efficiency

Therefore consume

kg( CO 2)/ kWh

CO 2


GWh (d)

GWh (P)

Mt CO 2

Coal - MPP






Longannet and Cockenzie both likely to be 'typical' UK efficiencies.

Gas - MPP






Combination of conventional steam cycle plant (at estimated 30-35% efficiency) and modern CCGT (at >50%), all at Peterhead.

Nuclear - MPP






UK average nuclear generating efficiency for 2002.







Used predominantly for nuclear stand-by.

Natural hydro






Minimum. Generating efficiency N/A.

Small/other renewable






Generating efficiency N/A. Composite of thermal, small hydro and wind - see Appendix 6 for details.

Small/other fossil fuel






Composite of mostly gas and oil (some coal) CHP/ small-scale. High efficiency if one considers that the heat is usefully used. Appendix 6 for detail.





CO 2/kWh generated


Based on generated electricity = Total CO 2 generated by primary fuels, divided by total units of generated electricity.

Pumped hydro




From DTI Energy Trends. Pumped hydro represents a means for storing electricity from other sources that would otherwise be lost.

Electricity to pump water


Need to subtract to avoid double counting. Typically 75% efficiency.

Other electric losses…


Self-consumed by MPP and a proportion of self-consumption by 'others', plus transmission & distribution losses. Calculated from DTI Energy Trends, Jan 2005.

Saleable elec


CO 2/kWh supplied


Based on 16.28 Mt of CO 2 divided by 40.102 TWh of usable electricity

Export to England & NI



DTI Energy Trends (Jan 2005) figure for 2002. The export figure to NI (and ROI) is to be confirmed.

Consumed in Scotland



See Notes below.

  • Gas-fired plant efficiencies can vary between 30% and 38% (for conventional, steam cycle generators) to 45%-60% (old - new CCGT operations). Peterhead is part conventional and part CCGT. An overall generating efficiency of 43% was estimated, consistent with the relative efficiencies of the two types of plant. Longannet can also use gas, in a gas re-burn zone, this is part of a NOx reduction strategy.
  • The nuclear generating efficiency figure of 37.6% was taken from DTI statistics.

As this figure is being used to estimate the associated CO 2 emissions (which is set at 0 kg CO 2/kWh), the exact value is not important for this study. This approach allows the results of the study to illustrate the fact that nuclear generation is also a source of low temperature waste heat, just as are other conventional generators.

  • Oil is used for stand-by generation for the nuclear generators on some of the remote small-scale generators (Highlands and Islands) and in some MPPs for start-up.
  • The small contribution from CHP operations to grid or direct sales will be highly efficient, typically 72%, if one takes into account their heat energy is also usefully used.
  • Renewable energy - some comments on this are included in section 5. 5.

As the Energy Study is to calculate CO 2 emissions from electricity based on Scottish consumption rather than generation, some of the above points are academic. Primary energy figures have been included to:

  • Provide an estimate of the total primary energy consumed by Scotland.
  • Populate the Sankey energy flow figures in section 4.
  • Provide a ball-park estimation of carbon emissions from a supply perspective.

Further details of the analyses used to arrive at the results below are given in Appendix 6.

4.1.2 Results: electricity supply

The headline Scottish 'supplied electricity' figure for 2002 is 32,068 GWh.

A further 3,288 GWh of useful electricity was generated then self-consumed by CHP/small-scale electricity generators, giving a grand total consumption of 35,356 GWh. However, as commented, much of this electricity would be generated from fossil fuel supplied direct to a site and thus would be recorded in the appropriate demand sector as fossil fuel consumption.

The grand total figure (of 35,356 GWh) is very close to the recently revised DTI statistics total of 35,360 GWh. The DTI figure is made up from estimated consumption from public supply (30,726 GWh) plus autogenerators (4,632 GWh). Furthermore, the DTI 'estimated consumption from public supply' figure was also close to their 'electricity sales to public' figure of 30,330 GWh, giving confidence to the totals 25.

A brief analysis of Scotland's electricity figures indicated that the generation mix changed between 2001-2 and is likely to have changed for 2003 and beyond 26.

From section 3, the bottom-up total electricity demand by Scottish Industry, Domestic, Services and Transport was 34,070 GWh. However, this figure was gathered using different criteria to the DTI statistics. It is not surprising that this 'bottom-up' figure is:

  • Higher than the 'supplied electricity' figure of 32,068 GWh, because the bottom-up figure will contain a contribution of electricity from autogenerators and some renewable sources.
  • Lower than the grand-total figure of 35,356 GWh, because many of the CHP units will be 'seen' in the bottom-up analysis as consumers of gas, oil and coal.

As such, all figures are considered to be in reasonable agreement 27. Unfortunately, given the nature of the published data, it was not possible to strip-out different types of generation and attribute to supply-to-grid, self-consume or autogeneration.

Finally, Scotland generated an additional 8,034 GWh of electricity, which was exported to England and Northern Ireland (some of this was then passed on to the Republic of Ireland). The CO 2 associated with this exported electricity (including a proportion of distribution, transmission, etc losses) will be taken into consideration when assessing the overall CO 2 emissions for which Scotland is ultimately responsible.

Primary and generated electricity figures are shown below:

Figure 11: Scottish electricity - fuel use & electricity output

Figure 11: Scottish electricity - fuel use & electricity output

Not all the electricity that is generated is used due to losses and exports. For Scotland, less than 70% of the generated electricity is consumed by a Scottish end-user. Some 13% is lost through self-consumption at MPPs, distribution and transmission losses, or storage losses. In addition, nearly 20% is exported to England and NI.

Figure 12: Scottish electricity - generation & use

Figure 12: Scottish electricity - generation & use

4.1.3 CO 2 emissions arising from electricity generation

As discussed in section 2.3, there are several ways of attributing CO 2 emissions to electricity 28. This topic is discussed fully in Appendix 7. For the Scottish Energy Study, we have used two models:

Model 1 considers Scotland within the UK framework and has taken a UK overall average,

Model 2 takes a Scottish view.

For the Energy Study, the UK standard CO 2/kWh for delivered energy has been used, irrespective of Scottish generation. Currently the DUKES factor for electricity is 0.432 kg CO 2/kWh. As such, for the Scottish Energy Study, the figures used are:

32.09 TWh electricity consumption, generating

Model 1: 17.33 Mt CO 2 emissions (at 0.432 kg CO 2/kWh)

Model 2: 16.28 Mt CO 2 emissions (at 0.406 kg CO 2/kWh)

The lower CO 2 totals estimated using Model 2 reflect Scotland's greater supply from nuclear power and hydro generation in 2002 than the UK average.

As commented earlier, Scotland's generation mix changes from year to year, owing, for example, to power station outages.

However, the utilisation of different MPP stations, the utilisation of pumped-hydro storage and the transfer (export) of power to England and NI are issues that the Scottish Executive has little influence upon, yet are all issues that can have a substantial impact on the total electricity generated in Scotland and its associated CO 2 emissions.

4.1.4 Scottish electricity generating capacity

This section summarises the current generating plant, before going on to look at planned changes, both to decommission existing plant and to apply for consent for new plant.

(a) Overview and Existing Plant

  • In 2002, Scottish generating capacity was 9.5 GW

Table 13: Major Scottish power plants (plus renewable)



Capacity MW

Assumed Closure Date

Chapelcross 29








Hunterston B
























  • With current decommissioning activities, 42% of generating capacity, i.e. 4.1 GW, of this will be out of use by 2023.
  • Historically, Scottish electricity demand has been increasing by, on average, 0.8% per annum.
  • Total supply increases by 2.24% (40,970 MWh in 2002) owing to exports from Scotland via the inter-connector to the English and Irish markets.

Figure 13: Scottish electricity generating capacity

Figure 13: Scottish electricity generating capacity

It is important to be aware that the ' MW capacity' figures are only part of any assessment of electricity generation, and capacity factors or utilisation must also be considered. For nuclear stations, capacity utilisation is high, typically 70-80% when in operation. However, nuclear generators are obliged to operate at a high base load even during periods of low demand. Hence, to meet the varying demand for electricity a combination of different types of plant is required.

  • Wind generation depends on the weather. Typically, the capacity utilisation ( i.e. actual/theoretical generation) is 25-30% across the UK; some sites in Scotland offer higher utilisation, closer to 40%.
  • Natural hydroelectricity is controllable, although the capacity factor is often <10%. The hydro plant at Alcan Lochaber is an exception to this rule; its capacity utilisation is high. Annual electricity generated is dependent on how 'wet' or 'dry' a year has been.
  • Gas and coal powered stations offer better on/off control, which is an important element when considering following electricity demand. Typically, gas generators (particularly CCGT) tend to be used in preference to coal: they use cleaner primary fuel and have a higher generating efficiency. Coal generators tend to be used for demand management, for example, at night or in winter. As such, their capacity utilisation and generating efficiencies are lower, although given their contribution to the strategic picture, viewing these figures in isolation would be unfair.

(b) Decommissioning

  • Two nuclear plants are expected to be decommissioned in the next two decades: Hunterston B in 2011 (or the end of 2015 with proposed plant life extension) and Torness in 2023 (at the latest by 2029). This would remove 2.3 GW or 24% of Scottish generating capacity. Nuclear retirement is not an exclusively Scottish issue.
  • Additionally, the progressive closing of old coal-fired plant will remove a further 1.8 GW of capacity or 18% of current generating capacity.
  • In total, decommissioning activities currently planned over the next two decades will remove 42% of current Scottish generating capacity.
  • In 15 years' time, only two of Scotland's existing large plants are expected to be in operation - Peterhead (gas-fired) and Torness (nuclear).
  • All nuclear plant could be phased out by 2023, all coal plant could be phased out after 2008 (existing fossil fuel plant opted out of the LCPD can operate for a maximum of 20,000 hours between 2008 and the end of 2015) and all of Scotland's thermal power stations could be closed by 2030.

(c) New Plant

Details of existing, consented and 'in planning' electricity generation for Scotland are shown below:

Table 14: Scottish power plants: existing, consented and planned30

Plant type

Existing ( MW)

Consented ( MW)

In planning ( MW)









Oil & Gas




Pump Storage




Landfill Gas








Onshore Wind




Offshore Wind
















By 2020, Scotland 'aims' to generate approximately 13 TWh/year from renewable sources (a renewable target of 40% of needs).

(d) Issues for Future Scottish Electricity Generation

If the anticipated closure plans were adhered to, and no new capacity built, Scottish generating capacity would reduce to 32% of 2002 levels in 2023. While future plans for some of Scotland's major power stations have been made known, these may change in response to market conditions. Similarly, plans for new power stations are commercial decisions for the electricity generation sector. Their decisions will take into account factors such as: future energy prices, electricity demands, the regulatory environment and new technical developments.

4.2 Oil refining/petrochemicals

This section examines the oil sector, in particular, the refining of oil for final users in industry, services, the domestic sector and for transport, as well as export from Scotland. Information is given on how this was calculated, followed by the results.

4.2.1 Approach taken to estimating Scottish oil supply

The analysis carried out does not include the energy use or emissions in the offshore oil industry. These emissions are excluded from the study as it is not possible to categorise which units are within 'Scottish' waters, as the demarcation is British and Norwegian, Danish, etc waters. Note: offshore emissions are not included in NAEI Regional data, although they are included in the EU- ETS (but here they are not attributed to any country).

Oil refineries can be either reported as an industry sub-sector, or treated as secondary fuel production (not unlike electricity generation). This latter approach is in keeping with the DTI's presentation of Energy Statistics and thus is, in the main, the way it has been presented in the Scottish Energy Study 31.

There is one major oil refinery in Scotland, at Grangemouth 32. This has a capacity of about 10 Mt oil 33, representing over 11% of the UK's 88 Mt capacity. Throughout the UK, refineries tend to operate close to capacity, and figures of 95%(+) are not uncommon. The Scottish operation is believed to be no different.

SEPA data suggest that 34 the main BP oil refinery at Grangemouth emitted 2,310 kt CO 2 to air in 2002. In addition, BP Exploration at the neighbouring Kinneil terminal emitted 460 kt CO 2 to air, giving a total of 2,770 kt CO 2. The adjacent BP Chemicals site was also a major emitter of CO 2, but the energy and CO 2 emissions from here will be included in the Scottish Industry demand sector (section 3.2).

Most of the oil-based fuel used to generate this CO 2 would be from crude oil fractions, extracted during the refining process, to generate both heat and on-site electricity. Some of this heat and electricity generation is via steam turbine CHP systems. Anecdotal feedback suggests that most of this energy would be taken from the low-value, difficult to sell fractions such as heavy fuel oil.

Back-calculating to energy would give:

  • HFO has a calorific value of 11,930 kWh/t and an emission factor of 0.260 kg CO 2/kWh.
  • 2,770 kt CO 2 emissions at 0.260 kg CO 2/kWh = 10.65 TWh
  • 10.65 TWh at 11,930 kWh/t = 893 kt oil-based product.

Below, some estimation has been made to calculate the balance between imported and exported refined-oil products from Scotland.

  • The capacity of the Scottish operation is approximately 10 Mt/y 35. If this figure is for crude product in, then at 95% capacity factor, this would be equivalent to 9.5 Mt crude oil processed in 2002. Subtracting the 0.89 Mt of crude oil that is self-consumed to generate on-site heat and electricity would mean that 8.6 Mt refined product was made in 2002.
  • Typically, 8% of output from a refinery is non-fuel products, such as naphtha, greases and lubricants, white spirits, etc. As such, the Scottish refinery produced an estimated 7.9 Mt of fuel product (= 92% of total refined product) plus 0.7 Mt of non-fuel product in 2002.
  • Using a weighted average CV for oil-based products of 12,595 kWh/t (see Appendix 8), 7.9 Mt of oil product would be equivalent to 99.6 TWh of refined oil. As Scotland itself consumes an estimated 61.1 TWh of oil (predominantly for transport - see section 3.2), this implies that, on balance, Scotland exports 38.5 TWh of refined oil fuels to the rest of the UK and overseas.

An analysis based on DUKES 2002 on refineries indicates that approximately 15-20% of the energy consumed within a refinery is electricity, 5-10% is natural gas and the remaining 75% is oil. However, it was not clear from DUKES whether this electricity and gas are imported or extracted from the crude oil. Earlier anecdotal feedback would suggest that it is from crude oil.

Further exploration would be required to:

  • Confirm that the above figures for 'electricity' and 'gas' consumption are self-generated from the low-value oil fractions, not imports.
  • Confirm that refinery capacity refers to quantity of crude oil processed and not quantity of refined product produced.
  • Better resolve the crude oil split into fuel and non-fuel fractions, in particular, whether there are issues to do with Grangemouth that would impact on the above analysis.

4.2.2 Scottish oil supply

Table 15 shows the estimated details of oil-based fuel consumption in Scotland.

Table 15: Headline estimate of Scottish oil refining

Approximate capacity

10 Mt/y

Estimated throughput

9.5 Mt/y

Emissions from Grangemouth & Kinneil, 2002

2.77 Mt CO 2

Energy self-consumed in process

10.65 TWh

Output of saleable oil-based fuel

7.9 Mt, or 99.6 TWh

Total oil-based fuel consumption within Scotland

61.1 TWh

Therefore exports (balance)

38.5 TWh