Scottish Government

Appendix 6 Electricity from DTI and other statistics: Generic issues from data handling, including efforts to avoid double-counting for the Scottish Energy Study

Electricity is the most complex fuel and perhaps the most difficult to clearly define. For the Scottish Energy Study, it is proposed to use a figure of 32,068 GWh as the 'headline' Scottish 'supplied electricity' figure for 2002. This electricity was generated predominantly from Scotland's three nuclear, two coal, one gas and several hydro MPPs, although the electricity sold-on from small-scale electricity generators or CHP is also included.

A further 3,288 GWh of useful electricity was generated and then self-consumed by CHP/small-scale electricity generators, giving a grand total consumption of 35,374 GWh. However, from the Energy Study perspective, this electricity would be mainly generated from fossil fuel supplied direct to a site and would be recorded thus.

The grand total figure is very close to the recently revised DTI statistics total of 35,360 GWh, 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 its 'electricity sales to public' figure of 30,330 GWh, giving confidence to the totals ⁷³.

The bottom-up assessment of electricity demand by Scottish industry, domestic, commercial/public sector/agriculture and transport was 34,070 GWh⁷⁴. 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 contains 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.

All figures are considered to be in reasonable agreement ⁷⁵. 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.

In addition, Scotland generated 8,035 GWh of electricity, which was exported to England and Northern Ireland (and some of this then on to ROI). The CO ₂ associated with this exported electricity (including a proportion of distribution, transmission, etc losses) needs to be taken into consideration when assessing the overall CO ₂ emissions for which Scotland is responsible.

Background and Introduction

There is potential to double-count, mis-count or misinterpret electricity figures from DTI and other statistics and other sources. This note covers how the study handled issues relating to:

1. Generating efficiencies.

2. Electricity self-consumed by MPP.

3. Electricity use for pumped hydro.

4. Renewable energy.

5. CHP and small-scale power.

6. Energy-in & energy-out for Scottish electricity.

7. Electricity balance: top-down estimation of saleable electricity.

8. Autogenerators.

It ends by discussing what information is to be used to generate the top-down figure for electricity energy supply for the WECE study.

Finally, this note summarises issues regarding raw data and its analysis, where it is believed more attention could help to provide a more accurate/robust set of electricity generation and consumption data. Although important, the effort needed to pay attention to these issues lies outside the immediate scope of WECE, as such they can only be identified and partially acted upon.

A6-1. Generating efficiencies

These were not available at the time of the study and so the following approach was used for MPPs:

• Nuclear: 37.6% - UK weighted average, taken from DTI statistics.
• Gas: Peterhead now known to be a mixture of conventional (@ 33-34%) and CCGT (@ estimated 55-60%). The figures provided by S&S suggest an overall efficiency of 43%; this figure will be used for the Sankey diagram.
• Coal: conventional. Longannet and Cockenzie are both relatively old coal-generators. It is known that the former supplements its fuel with dried sewage sludge waste, but the figures have not been declared in DTI statistics. As such, until we get better site-specific data, a UK average generating efficiency of 37% will be assumed.
• Oil: very little used, predominantly as stand-by for nuclear. Generating efficiency of 33% has been assumed.

A6-2. Electricity self-consumed

A6-2.1 By MPP

Typically, of electricity generated by large generators ( MPP), 5% is consumed by the generators - i.e. it never reaches the end-user.

DTI Energy Trends had 3,492 GWh consumption for 'self-consumed by MPP plus pumping water'. Recently, this figure was revised to 3,459 GWh. Using published DTI data on output of pumped hydro (622 GWh) and an assumed efficiency of 75%, estimates the electricity used for pumped hydro as 829 GWh. This implies that 2,630 GWh were self-consumed by MPP generators, which represents over 6% of the total Scottish power generated in 2002. It is believed this figure is not unreasonable, given that Scotland has a high proportion of nuclear power ⁷⁶.

This self-consumed electricity needs to be subtracted from the total generated.

A6-2.2 By others

Similarly, 'other' generators in Scotland self-consumed 240 GWh electricity. It is believed that most of this will be self-consumption by the CHP and small-scale fossil-fuel power generators. This needs to be taken into account and subtracted from the total generated.

A6-3. Pumped hydro

In Scotland, some electricity is consumed to pump water uphill, for later release and generation of pumped hydro ⁷⁷. Using DTI data, the electricity consumed to generate 622 GWh (at 75% efficiency) is 829 GWh.

The electricity generated from the conventional (and renewable) sources still counts as generated electricity, even though it never reaches market. Thus, the 829 GWh needs to be subtracted from the total figure for electricity generated. This will be represented in the Sankey figure as a return loop of 829 GWh creating 622 GWh of electricity with 207 GWh generating losses.

A6-4. Renewable energy

• Total 'hydro natural flow' MPP = 3,693 GWh.
• Total 'other' generation = 5,619 GWh, of which:
  237 = thermal renewable, 762 = natural hydro, 406 = non-thermal renewable (wind);
  i.e. 1,405 GWh total 'other' renewable.
• Total renewable in Scotland = 3,693 + 1,405 = 5,098 GWh
• Not all of this renewable energy generation will be supplied through the grid.
  For example, most if not all of the electricity at the hydro plant at Alcan Lochaber will be seen as autogenerated, i.e. would not be exported.

A6-5. CHP/small-scale electricity generation

Most of the remaining 'other', non- MPP generators will be CHP units or small-scale dedicated power plants operating at large (mainly industrial) sites. Several of these units will be counted as autogenerators and/or as part of the oil-refinery energy data.

The DTI provides an assessment of the CHP generating capacity, etc for the DAs plus English Regions.

In 2002, Scotland had 85 schemes with an electricity capacity of 743 MW, and generated 4,214 GWh of electricity plus 14,180 GWh heat from 25,876 GWh fuel ( Energy Trends - special feature - Sep 2004). These figures are slightly lower than the January 2005 figure of 4,227 GWh electricity generation. The latter figure has been used because we have a breakdown of primary fuels.

We also know for the UK in 2002:

• Total fuel input for CHP = 123,888 GWh.
• Electricity generated = 24,485 GWh, of which 7,958 GWh (32.5%) were exported, approximately 55% directly to other consumers and 45% via the grid network ⁷⁸.
• However, for Scotland the exported proportion is less. Only 747 GWh were 'transferred from other generators to public supply', which represents only 17.7%. This means that the 4,227 GWh of electricity would be split: 3,480 GWh own-use and 747 GWh exported.

Applying these figures proportionally to the non- MPP 'other' fossil fuel generators in Scotland would give:

The own-use electricity would be 'seen' in the Scottish Energy Study as gas, oil (or coal).

One has to be aware that the 747 GWh of exported electricity would be 'seen' twice:

1. Once as direct sales of gas, oil (or coal) to the demand end-user.

2. Then again as electricity sales from CHP operators to other users.

Or, conversely, a portion of the gas, oil (or coal) consumption by industry and other sectors will, in fact, be to generate 747 GWh of saleable power.

The overall efficiency of these units is high because the operator consumes the heat (or it is occasionally sold on). For 2002, the average UK efficiency was 72%. This means that approximately 1,039 GWh of primary fossil fuel consumption by end-users was, in fact, used for generating 747 GWh of electricity.

Depending on presentation, this figure should be subtracted from Transco and other supply figures of sales to end-users in Scotland. The figure is fairly small compared with the grand total consumption and as such it is recommended that one remains aware of the fact that a proportion of direct gas sales are, in fact, for electricity generation and, where necessary, make minor adjustments to the declared figures.

A6-6. Energy-in & energy-out for Scottish electricity

A6-6.1 MPPs

Figures extracted from DTI Energy Trends

A6-6.2 'Other' smaller renewable sources - see section 5.5

A6-6.3 Estimation of CHP & small-scale generator supply to grid or sold-on

A6-6.4 Pumped hydro

Pumped hydro is generated from electricity generated from MPP or others. As such, it can be considered a tertiary fuel. The 622 GWh of electricity required to generate is to be subtracted from the available electricity figure below. Handling it any other way would skew the overall generating efficiencies and CO ₂/kWh figures.

A6-6.5 Total

Thus, for Scotland in 2002, 45,310 GWh of electricity was generated from 109,755 GWh of primary energy, with 64,238 GWh losses.

These figures exclude:

• Estimated electricity generated then self-consumed by industrial and other sites.

A6-7. Electricity balance: top-down estimation of saleable electricity

Total electricity generated available for sale was 45,310 GWh. From this, one has to subtract:

This analysis gives a residue of 32,068 GWh saleable units of electricity. Clearly, this is somewhat less than the 'headline' figure of 35,356 GWh but one must recognise that 3,298 GWh will be the electricity self-consumed by CHP/small-scale electricity generators that consume their own electricity (=3,480 GWh from from DTI 'Energy Trends' - Dec 2004 minus 198 GWh self-consumption during generation) ⁷⁹.

A6-8. Autogenerators

Discussions with our CHP experts indicate these are large consumers of electricity generated on-site ( i.e. not supplied for sale by MPP and other generators via the grid). For Scotland in 2002, this was 4,632 GWh of electricity. This represents approximately 2,000 more GWh than the previous published statistics, the reason for the large increase is being explored with the DTI.

A proportion of these autogenerators will have already been counted in the CHP/small-scale electricity generator figures for on-site consumption, or as small-scale (and MPP) renewable energy sources above. As such, a proportion of their consumption will be counted as electricity generation at an industry (or oil-refining) site.

A proportion of their consumption will be seen as fossil-fuel consumption by the bottom-up 'demand' sector, again predominantly industry or oil refining.