At 5.30 in the late afternoon the average UK house is using about 130 watts of electricity to power lights. In the winter months this number rises sharply, probably to around 200 watts. 27 million households are consuming over 5 gigawatts of electricity just for lighting in the early evening of the darkest month. The maximum need for electricity last year occurred just after 5pm on November 4^th when the major generators delivered almost 53 gigawatts. At the moment of highest electricity need, domestic lighting was therefore using about 10% of the country’s power production. The easiest way of cutting this is by banning halogen bulb sales and obliging consumers to replace them with equivalent LEDs.

As conventional power stations close, the gap between the total generating capacity in the UK and peak winter demand is narrowing sharply. A ban on halogen lamps will dramatically improve the UK chances of ‘keeping the lights on’ in winter by shaving the top of the daily winter peak of power demand.

Halogens are not quite as inefficient as the old fashioned incandescent bulb but they use far more electricity than LED equivalents. A 35 watt bulb can be replaced by 5 watt LED of almost identical light quality. Many kitchens and living areas contain several hundred watts of halogen bulbs and all this lighting could be replaced by equally effective LEDs.

Cutting domestic lighting demand is the simplest way of reducing the maximum need for electricity. And it would reduce consumer bills and make a substantial dent in the need for electricity users to pay (indirectly via the so-called ‘capacity mechanism’) for fossil fuel power plants to stand waiting just in case the other generators couldn’t supply enough power. In addition, the reduction of peak demand would cut the need for extremely expensive grid upgrades. There is real social value in moving the country off halogen bulbs as fast as possible.

Domestic electricity demand

DECC has been quietly investigating ‘Time of Use Tariffs’ for some time. The idea is that by making electricity more expensive between 4pm and 8pm it can cut the peak demand for electricity from households. Research work published over the summer showed how power needs varied for a sample of households over the course of the day. During the working day electricity consumption is about 500 watts. This rises sharply from about 4pm as people return home and turn on TVs, washing machines, heaters and other appliances. By 5pm, average household need is almost 750 watts. The chart below estimates average use across the year. In the winter, the early evenings would see a much larger increase in domestic electricity use.

Lighting, cooking and TV use are largely responsible for the rise in demand after 4pm, as the chart below shows. I don’t think we can force people to buy smaller or more efficient TVs or cook with gas, nor do I think that increasing prices sharply on winter evenings would work. But I do think we can rapidly accelerate the move to LEDs instead of halogen bulbs. It’s mildly illiberal but then so was banning lead in petrol or smoking in enclosed spaces.

National electricity use

The rise in domestic use of electricity is occurring while offices and factories are still using large amounts of power. So the overall peak in winter demand occurs in the late afternoon. After a period of almost flat national electricity consumption on last winter’s peak day of around 46 gigawatts, the additional household demand after 4pm added most of the 7 gigawatts rise to almost 53 gigawatts at about 5pm. The chart below shows the pattern of national demand on 4^th December 2013 when last winter’s peak usage occurred.

We really do want to reduce this peak. If we ever actually run out of power, it will be because of the sharp bump in demand for a few hours in the period between November and February. A large number of very clever people are spending a lot of hours working out how the UK is going to cope with unexpectedly high demand on particularly cold or still days when the wind turbines aren’t turning. All sorts of expensive technologies are being investigated and National Grid is offering increasingly large sums to persuade businesses to turn off their machines at times of highest demand.

Last year, the National Grid said it restrained peak winter evening demand by about 2 gigawatts on the coldest day. Let’s compare this with the possible impact of banning halogen bulbs. There are about 27 million homes in the UK. If the average home reduced its need for lighting by 100 watts on winter evenings, peak demand would be cut by 5%, or well over the 2 gigawatts that has been very expensively achieved by other means by the Grid. This 5% cut would be achieved by simply replacing an average of fewer than four 35 watts halogens with 5 watt LEDs. The quality of LEDs is now almost the same as halogens with ‘warm white’ bulbs delivering light of identical colour. 5 watt halogen replacements are on sale for around £10-12, meaning that the total cost of replacement will be less than £50 for the average household.

The savings in domestic bills alone will be £20 or more a year. Payback will be in two years or so and the ten year lives of LEDs will mean that far fewer replacement bulbs will be needed after that point. The National Grid will need to spend far less on keeping generating capacity mothballed in case it is needed. Carbon emissions will fall disproportionately because this standby plant will be the most polluting power stations in the country. Grid stability will be enhanced because some of the sharp ramp up in power production from 3.30pm onwards will be avoided. Air pollution on cold, still December days from burning coal will be avoided.

Over the last few years the EU has seemed to back away from a ban on sales of halogen. As LED quality improves, and costs fall this policy needs to be re-examined both in Brussels and London.

(This post was re-published in The Ecologist on October 7th 2014)