HC 562 The effect on energy usage of extending BST

Memorandum submitted by Dr. Mayer Hillman University of Westminster (BST 02)

My name is Mayer Hillman. I am Senior Fellow Emeritus at Policy Studies Institute (formerly known as PEP – Political and Economic Planning) where I have been engaged for 40 years in social scientific research. In the mid-1980s, following the observation on our ‘waste of daylight hours’1, I undertook a comprehensive study of the wide-ranging social and environmental consequences of aiming to achieve a better matching of our daily and waking hours. By examining all facets of daily life and working practices, it established that the advantages would far outweigh the disadvantages. The first report on it was published by Policy Studies Institute in 19882. This was followed by a Government Green Paper on the subject a year later3 and, in 1993, an up-date of the 1988 PSI report4. A further study which is focused exclusively on the implications of such a change for Scotland is to be published at the end of this month5.


1. Energy consumption would be affected in four ways if clocks were put forward by one hour in summer and winter. After exploring available evidence on these aspects , this Memorandum concludes that the overall outcome would be likely to be favourable, albeit marginally. The only reliable way of determining this precisely would be to undertake a trial period with the clock change. However, it would appear to be extremely unlikely to affect the judgement that the UK ’s adoption of the SDST (Single Double Summer Time) clock regime would be highly desirable as the benefits outweigh the disadvantages to such a marked degree .


2. The great majority of the UK population get up well after sunrise for most of the year, but are then denied opportunities for outdoor activity by the onset of darkness at the end of the day. The most realistic and studied proposition rectify this anomaly has been to move UK clocks ahead of their current setting to GMT+1 in winter and GMT+2 in summer – essentially advancing them by one hour throughout the year.

3. The proposal, sometime known as SDST (Single Double Summer Time), would enable UK citizens to make better use of the available daylight. In reality, for the great majority of the population, it would entail the loss of an hour of morning daylight in the winter months only, but this would be substantially offset by the additional hour of late afternoon or evening daylight on every day of the year.

4. Over the last 20 years, politicians have been looking at this issue more closely, with an eye to possible reform. Many Early Day Motions on the subject have been put forward and many unsuccessful bills proposed to Parliament. They have included the one by Tim Yeo, MP in 2006 (Energy Saving [Daylight] Bill) which called for a three-year experiment to advance the clocks by one hour throughout the year – similar to what happened during World War 2 though this was achieved with four annual clock changes. Earlier this year, the Daylight Saving Bill has been taken forward by Rebecca Harris, a newly-elected MP.

5. This short Memorandum has been undertaken to highlight the likely effects of this clock change on policy concerned with drastically limiting the use of fossil fuels and ensuring the security of the UK’s energy supplies.


6. The relationship between our waking hours and daylight hours affects energy consumption in four distinct respects :

f irst, demand for artificial lighting in home s , offices, industrial and commercial premises , streets, and so on;

second, hourly changes in demand affecting the efficiency with which electricity power generators can balance daily peaks in the morning and afternoon ;

third, during the heating season, the variation in demand due to changes in the external ambient temperature through the day; and

fourth, in the absence of legislation controlling the extent of petroleum use, the availability of daylight enabling more activities outside the home, especially daylight - dependent ones , thereby affecting the demand for transport fuel, . especially for leisure travel .

The demand for artificial lighting

7. Demand for artificial light in the home is higher in the winter than in the summer, reflecting principally the monthly variation in the hours of the day between sunset and going to bed. Most people get up well after sunrise for about nine months of the year, and therefore do not need to switch on lights in the morning. But they are highly likely to go to bed after sunset throughout the year, making the need in the evening sensitive to the time at which sunset occurs. Advancing clocks by one hour would lower this demand on every evening of the year whereas demand in the mornings would only rise in the winter months.

8. A detailed study by the Cambridge University Centre for Technical Management of the likely changes in electricity use in the home if clocks were maintained on GMT+1 hour during the winter months alone concluded that average demand would reduce by at least 0.3%6. Further reductions on a not dissimilar scale could be predicted if clocks were put forward by the additional hour during the seven months of summer time from the end of March to the end of October. In a just-published study by the author on the subject, it was established that the effect of the clock change would be to reduce the number of hours for which artificial lighting would be required by about 0.8%5.

9. At present, lighting accounts for about 13% of all domestic electricity consumption in the UK7. It could be expected that the effect of putting clocks forward by an hour throughout the year would result in an overall saving of electricity bills. Calculations based on data in the report referred to in the previous paragraph5 show that the effect of this would be to lower demand for lighting in the region of 9% and therefore to annual savings for domestic consumers in the UK of over £100 million.

1 0 . Lighting demand in offices, industrial premises , and public buildings accounts for about 30% of electricity used in the m. Some small reduction in this sector is also likely to be achieved with the clock change as the number of hours during which it was needed would decrease. However, i t is difficult to estimate with any precision the consequent saving s as published statistics do not differentiate between electricity used in offices and shops within the commercial sector and, in any case, people working in offices tend to be less careful about switching off lights when they are not needed.

11. At present, the clock change would not lead to reductions in railway stations and other public places such as for street lighting due to the now-common practice of leaving lights on all night for security reasons. (Having said that, trials are now taking place across the UK which should ensure more efficient use of street lighting.)

Balancing the two daily peak demands for electricity

12. The Cambridge University Centre for Technical Management study cited earlier also examined the impact on the peak demand for electricity of maintaining clocks throughout the year one hour ahead of GMT. This showed that the lighter evenings would reduce peak demand by just over 4 % 6 .

13. At present, the higher peak demand for electricity in the late afternoon than in the morning results in it being met either by using less efficient spare generating capacity (such as oil-fired stations and pumped-storage facilities) or by imports from France by cable under the English Channel (accounting for little more than 2% of total electricity used in Great Britain). Owing to the peak demands in France and Great Britain differing by price and time of day, it would be difficult to determine the outcome of the clock change for generating companies’ costs. To do so, it would be necessary to compare the price of imported electricity with that of using the less efficient spare capacity at the specific time it was needed. However, there is sufficient understanding of the likely consequences of achieving a better balance between the morning and evening peak to anticipate a small beneficial outcome. A ‘conservative’ estimate for the UK as a whole indicated that CO2 emissions from power stations would drop by about 450,000 tonnes if clocks were advanced by one hour solely in the winter months from the beginning of November to the end of March6. Thus, further consumer savings on electricity bills are possible though they would be dependent on the generating companies passing these on to their customers.

The demand for heating

1 4 . The better matching of waking hours with the hours of daylight could also affect the extent of heating needed in the home during the winter months owing to the relationship of the time of the day when people are ‘up and about’ and the changes in the ambient outdoor temperature. Advancing the clocks by one hour would mean that people would be getting up closer to sunrise.

15. Two consequences of this need to be borne in mind: first, in the study referred to earlier, the temperature at 8am during the winter months requiring central heating is identical to the current winter GMT clock as it would be with the clock advanced by the one hour and very similar at 5pm, that is around the time of sunset 5 . Although the analysis was limited to data collected at the Meteorological Office station situated between Edinburgh and Glasgow, there is no strong reason to believe that dissimilar results would be found from data collected in other regions of the UK.

16. On the other hand, it can be predicted that there would be an hour’s marginal increase in demand in the morning as the average temperature at around 8am is between 1° and 2°C lower than the early evening average around 5pm. A special study would be required to establish whether, as expected, the consequent change in heating costs would be more than minimal.

Demand for fuel for travel

17. Another impact of the clock change on fuel use is likely to stem from an increase in travel mileage (and therefore transport fuel consumption) resulting from the wider opportunities for leisure activities in the evening. In the UK as a whole, people spend about 60% less time watching television in summer than in winter, suggesting a strong relationship between such sedentary activities and available daylight hours.

18. The PSI report just published included the findings of special tabulations commissioned from the National Travel Survey on monthly changes in the incidence of travel to participate in sports. It revealed that during the two months in the spring and in the autumn, over a quarter more of these types of journey was made with the summertime clock on GMT+ one hour than with the wintertime clock on GMT.

19. Whilst part of the explanation for this is obviously attributable to temperature differences, daylight also clearly plays a significant role. It is pertinent then to note that the report also established that the clock change would increase the annual number of what it called ‘accessible’ daylight hours for adults by around 300 hours – these are typically the hours between 10am and sunset on the two weekend days and between 5pm and sunset on the five weekdays. (The equivalent for children is less in the region of 200 hours – as for part of the year, they go to bed before sunset). However, no studies have been undertaken to reveal the extent to which lighter evenings would lead to more leisure activity making use of cars.


20. It is clear that, in respect of the four themes addressed in this Memorandum, energy consumption would be affected by setting clocks forward by one hour in summer and winter . In the case of the first two, the benefits would be positive whilst in the latter two, they would be negative . In the absence of evidence from a systematic and detailed evaluation of all four effects, it could be surmised that the overall outcome would be favourable, albeit marginally. The only reliable way of determining this would be to undertake a trial period with the clock change. However, on the basis of the evaluation above, it would appear to be extremely unlikely to affect the judgement that the UK’s adoption of the SDST (Single Double Summer Time) clock regime would be highly desirable as the benefits outweigh the disbenefits so marked ly4.

October 2010


1 Hillman, M., A Waste of Time: a Time of Waste, Annual Conference of ASSET (Association for Social

Studies of Time), Cambridge, (Unpublished), 13 April 1985.

2 Hillman, M., Making the Most of Daylight Hours, Policy Studies Institute, 1988.

3 Home Office, Summer Time: A Consultation Document, Cm 722, HMSO, 1989.

4 Hillman, M., " Time f or Change Setting Clocks Forward by One Hour t hroughout the Year:

A New Review of the Evidence ", Policy Studies Institute, 1993

5 Hillman, M., Making the Most of Daylight Hours: The Implications for Scotland, Policy Studies

Institute, (in press).

6 Hill, S.I . , Desobry, F ., Garnsey, E. W., Chong, Y.-F. The impact on energy consumption of daylight

saving clock changes , Energy Policy, Elsevier, 2010.

7 Department of Energy and Climate Change, Digest of Energy Statistics 2010 and Energy

Consumption in the UK and Regions: Domestic data tables 2010.