HC 562 The effect on energy usage of extending BST

Memorandum submitted by National Grid (BST 03)


Executive Summary

1. National Grid welcomes this opportunity to contribute to the Committee’s inquiry into the effect on energy usage of extending British Summer Time (BST). National Grid’s analysis suggests that the extension of BST through the winter would result in a small reduction in energy usage.

2. National Grid has undertaken research work with Cambridge University to analyse the effects of extending BST on electricity demand. This analysis suggests that throughout winter there would be a reduction in the daily peak demand and an increase in morning demand, leading to a small reduction in overall energy volumes.

3. The extension of BST would have an effect on marginal plant during early and late winter. There would also be an effect on Interconnector flows as the UK and mainland European demand peaks align, leading to a higher probability of increased peak prices in low margin scenarios that affect either market.

4. There is anticipated to be less impact on the usage of gas than electricity. Gas is balanced on a daily basis and demands are likely to remain largely unchanged with any marginal increase in the morning being offset by a similar reduction in the evening.

Introduction to National Grid

5. National Grid owns and operates the high voltage electricity transmission system in England and Wales and, as National Electricity Transmission System Operator (NETSO), operates the Scottish high voltage transmission system. National Grid also owns and operates the gas transmission system throughout Great Britain and through the low pressure gas distribution business, distributes gas in the heart of England to approximately eleven million offices, schools and homes. In addition National Grid owns and operates significant electricity and gas assets in the US, operating in the states of New England and New York.

6. In the UK, National Grid’s primary duties under the Electricity and Gas Acts are to develop and maintain efficient networks and also facilitate competition in the generation and supply of electricity and the supply of gas. Activities include the residual balancing in close to real time of the electricity and gas markets.

7. Through its subsidiaries, National Grid also own and maintain around 18 million domestic and commercial meters, the electricity Interconnector between England and France, and a Liquid Natural Gas importation terminal at the Isle of Grain. In addition, the wholly owned subsidiary National Grid Carbon Limited has advanced the transportation and storage elements of the Carbon Capture and Storage (CCS) supply chain.

Effects on energy usage of extending British Summer Time

Electricity - research

8. National Grid has previously undertaken research work with Cambridge University to model and investigate the impacts of moving to a year round BST. This resulted in the publication of Daylight Saving, Electricity Demand and Emissions; Exploratory Studies from Great Britain, Chong et al (2009) [1] , The Impact on Energy Consumption of Daylight Saving Clock Changes, Hill et al (2010) [2] and a commissioned piece of work that is unpublished, final Report to National Grid on Potential Impact of Change in the UK Clock Time regime, Garnsey, (2009). Research work has also analysed the 1968 to 1971 experimental period where BST was adopted year round and reviewed some of the recent international experiences (see Appendix 1)

Electricity - System Demand

9. Electricity demand is directly linked with activity and sleep patterns. Whether or not activity take place during sunlight hours has an effect on the energy consumed. The extension of BST changes whether activities take place during sunlight hours (as shown in Figure 1).

Figure 1 - Activity and Sleep time in GMT and GMT + 1

10. Following the autumn clock change there is a step change in the daily demand peak (as shown in Figure 2). The mid-winter peak is referred to as the darkness peak. The darkness peak occurs when the tea-time peak and the lighting peak occur at the same time resulting in a sharper higher peak than the rest of the year. Prior to clock change the tea-time peak and darkness peak occur at different times resulting in a wider lower overall peak when compared to the post clock change darkness peak.

Figure 2 - Change in demand levels over clock change

11. The extension of BST through the winter would remove the step change that currently occurs at clock change, however, the tea-time peak and the lighting peak will still move closer together naturally as sunset becomes earlier. As the peaks move close together in the middle of the winter (December and January) there would be similar size demand peaks as the peaks during a winter where GMT was adopted. The net effect on peak demand therefore presents benefit during the ‘shoulder’ months of the winter (November, February and March) as shown in Figure 3.

Figure 3 - Peak demand forecasts over winter with GMT and GMT +1

Please note: Peak demand forecast by calendar week. The autumn clock change occurs at the end of week 43 and the spring clock change occurs at the end of week 12

12. During mid-winter, peak demand would continue to take place at 17:00 to 17:30 in an extended BST scenario as it currently does in the GMT scenario. The largest reduction in energy usage would occur over the peak during the shoulder months, on average a 1300 MW reduction in total system demand. During mid-winter an impact of up to a 500MW (0.8%) reduction in the peak demand is possible but represents a high case view of the impact (a full breakdown can be seen in Table 1). The change over mid-winter is driven by slightly warmer temperatures at the time of the demand peak and by a small decline in lighting load during the same time.

Table 1

Impact of extending BST through the winter



Other End User Behaviour

On mid-winter daily demand peak

200 MW reduction in peak demand

300 MW reduction in peak demand

Negligible impact

On shoulder month daily demand peaks

800 MW reduction in peak demand

500 MW reduction in peak demand


On daily energy volumes

< 1 GWh (0.1%) reduction

< 1 GWh (0.1%) reduction


13. Looking at the whole day there would be marginally more demand in the morning if the BST scenario was adopted, due to increased lighting requirements. This would net off some of the evening reductions leaving a small benefit over the whole day.

14. There would be no change to demand in summer as usage and behaviours would be the same as they currently are.

15. In summary, if BST were extended through the winter;

· Daily demand peaks during the shoulder months would decrease by up to 1300 MW.

· The December and January demand peaks would be largely unaffected with a high case view of a 500 MW (0.8%) reduction.

· Morning demand would increase throughout the winter.

· Daily energy volumes would decrease by up to 0.1 GWh.

Electricity - Margin

16. The difference between the demand forecast and available generation is referred to as surplus. During the year there is a requirement to use some of this surplus for reserve requirements to enable secure operation of the transmission system. The remaining surplus is referred to as operating margin. A transmission system with only enough generation to meet the demand and the reserve required would have no operating margin. Hence the minimum amount of surplus and therefore operating margin occurs around the winter peak.

17. Investment signals for the construction of new generation are based around the winter peak requirements. With the adoption of BST there would be a larger amount of surplus generation in the shoulder months because of the lower wider demand peaks during this time (as shown in Figure 4). This would reduce the running hours of the marginal generation plant that currently operates mainly over the winter peaks. The marginal generation which is used to cover operating reserve in the winter peak would, therefore, be expected to operate less in a BST scenario. This would provide less of a signal for new marginal plant to be commissioned going forward and could lead to a reduction of operating margin providers.

Figure 4 - Energy Surplus Levels over the winter with GMT and GMT +1

Please note: Peak demand forecast by calendar week. The autumn clock change occurs at the end of week 43 and the spring clock change occurs at the end of week 12

18. Last year operating margin was provided primarily by coal or gas plant. This contributed to a fall in margin costs when compared to previous years when other generation such as oil fired plant were used. In an extended BST scenario where it would be expected that there would be increased levels of surplus, operating margin would still be provided mainly by coal and gas. As margin would still be provided by the same plant type a slight reduction in margin value from current levels may be expected; however a step change in margin cost observed since 2008/09 and attributed to limited requirement to warm oil generation for margin would not be expected.

Electricity - Interconnector Flows

19. National Grid’s analysis suggests that the extension of BST would also result in the demand peaks of the UK system occurring at the same time as the demand peaks of mainland Europe. As the interconnection between the UK and other European systems increases the ability to transfer energy between the markets of the UK and mainland Europe will increase. Previously, due to the charging methodology of interconnectors in the UK, over the winter peak in the UK a 2 GW import from France has been seen. With the changes to the charging regime of interconnectors the flow of energy between the UK and mainland Europe is expected to follow price.

20. In the event of a large loss of surplus (due to either loss of capacity or severe weather events) in either the UK or mainland Europe there would be an associated wholesale price rise. The extension of BST, with the peaks across the UK and mainland Europe aligned, could increase the probability of increased price rises in both markets.

Gas - System Demand

21. There is no recent analysis of the effect on gas usage from extending BST, however, it is generally understood that there will be no material impact on either annual or peak demand. The daily balancing period for gas rather than the half hour periods for electricity also lessen any potential impact.

22. The use of gas for heating requirements is expected to remain largely unchanged by the BST scenario as UK housing stock would require similar net energy over the day. There could be some small effects of an increase in non daily metered (NDM) gas consumption in the morning which would be expected to be offset by a similar reduction in the evening.

23. For gas fired power generation, there could be a small within day shift to reflect changes to within day electricity profiles. These are however expected to be relatively small and would probably only be noticeable if gas generation plant was providing the within day power generation profile. The net energy usage over the day would also be broadly neutral.

October 2010

Appendix 1

Electricity - International Experience

24. The State of California in the US extended DST (Daylight Savings Time) by three weeks in the spring and one week in the autumn of 2007. Statistical analysis of energy consumption showed little or no effect on the total energy consumption across California. Given natural variation in consumption a change of electricity usage could have been 1.5% without effects showing up statistically, the most likely approximation from the statistical analysis is a 0.2% decrease in electricity usage during this time period.

25. The State of Victoria in Australia advanced spring DST by two months in 2000 to accommodate the Olympics. The demand on the morning peak increased and tended to negate the benefits of the reduced evening peak load.

26. Other countries including Morocco, Japan, China, Tunisia, Pakistan and the Philippines have all experimented with changing DST with minimal reductions in energy usage reported.

Electricity - British Standard Time Experiment 1968-1971

27. In 1968 the UK began a three-year trial of so called British Stand Time (BST) which was implemented all year round. The clocks were advance one hour in March 1968 and not put back until October 1971. A review of this trial concluded that it was difficult to quantify important advantages. Demand for electricity reduced by 3% in the evening period but increased by 2.5% in the morning period. The net benefit of energy and demand was not considered adequate for the trial to be continued.

[1] http://www.ifm.eng.cam.ac.uk/people/ewg/091022_dst.pdf

[2] http://www-sigproc.eng.cam.ac.uk/~sih22/hill_desobry_chong_garnsey_10.pdf