Thursday, 5 April 2012

Shedding some light on commercial lighting

After my last blog post looking at electricity usage in Loughborough as the first part of an Energy Descent plan for Loughborough, my chum Martin asked what proportion of energy is wasted lighting up offices and shops when they are closed?  This is a very good question as I've often bemoaned the lights left on in shops when I walk through the town centre late at night.

At the University where I work some of the offices have motion sensors attached to the lighting, so the lights switch off 15-20 minutes after the last people have left (or if I sit too still in the evening!).  Not all the University buildings have this feature, and even in buildings where some offices do have it other areas don't (for example I often have to turn off the lights in the kitchens and mezzanine service areas on my way out, as they aren't on sensors and most people don't seem to know what the little switch on the wall does, despite having energy saving advice stickers attached to them recently!).

So how much energy are these shops and offices using, and can we work out (or at least guesstimate!) what sort of energy is being wasted by leaving the lights on all night?  The first question is quite easy to answer, because the DECC have a handy summary of "service sector"  energy use(which includes retail and commercial offices, as well as sports facilities, government offices, health, education and few other bits and bobs.  It doesn't include the "industrial" users such as factories, mines and construction).

The summary tells use that lighting is responsible for 21% of the sector's total energy use, which in turn was 18,357 thousand tonnes of oil equivalent in 2010.

Now what we need to do is convert "thousand tonnes of oil equivalent" into something a bit more familiar - good old kWh.  The conversion factor is quite simple:

1 ktoe = 11630000 kWh

So the 18,357ktoe is equivalent to 213491910000kWh, or  213.49191TWh.  The lighting is 21% of that, so 44.8333011TWh.

Now that's a fair chunk of energy in lighting all those offices, shops, schools, warehouses, etc.  But what proportion of that is unnecessary?  I guess we now need to think about what we mean by "unnecessary"?  There's some obvious ones:
  • Lighting the internal areas of shops and offices when there's nobody working there,
  • Lighting external areas when there is nobody around in the wee hours,
  • Uplighting buildings for purely aesthetic reasons (some of which seems to be left on during daylight!).
But what about the less obvious wasting of energy for lighting?  For example there's some evidence that since the 1950s there has been an increasing amount of "over illumination", especially in parts of the retail sector.  If we've got people using more light than they really need for tasks, then that's wasting energy.

There's also the plea that some people raise that lights are left on at night for security.  The idea is that you'd be able to see criminals doing their nefarious deeds if the rooms are all illuminated.  However it doesn't seem to work out like that - if there are few people around in the middle of the night there aren't going to be many witnesses.  Even if there were passers by, seeing lights being turned on or torches flashing in an otherwise normally dark building may be just as good a give away of naughtiness happening.  Indeed the criminals usually need light to do whatever it is they shouldn't be doing, so leaving lots of lights on can actually help them.  Councils that have dimmed or turned off street lights have sometimes recorded falls in levels of crime for example.

So how do we find out how much of that ~45TWh of lighting energy is being burnt pointlessly?  That's not easy to answer, especially in our increasingly 24 hour world where some shops and offices never close.  I've had a good old trawl through the Interwebs with Mr Google, and there's a distinct lack of hard data we can use to determine the answer to this question.

One paper I did come across had an interesting graph for a real London office that showed that the base load (ie the power used all the time, irrespective of whether people were using the building or not) was about 60% of the peak load when the workers were in. I've seen similar base load charts from the University's Sustainability team's energy monitoring of campus buildings.

Now this base load power use wasn't just lighting but also other electricity usage such as leaving IT equipment on and air conditioning running 24/7.  Even so, it shows that there's a lot of overnight energy being used in typical offices and we already know from above that office lighting is one of the highest electricity users overall.  If the 60% of the peak lighting is begin left on overnight across the country and not being used between (say) 10pm and 6am in most buildings, then we can guesstimate the wasted power.

Lets call the amount of base load lighting power used each hour p.  Then we'll use 8p at night and 16p of base load during the day.  To keep things simple lets assume that everyone comes in at 6am and turns on all the extra peak stuff at once, which then stays on until 10pm (it doesn't - this over estimates peak loading somewhat so will make our base load figures a bit low.  But heck, this is very rough guesstimate territory now!).  This means we'll use an extra 16 hours of the 40% peak power, which is 16 times 4p/6.  Lets assume this happens every day of the year, and use this to work out out a value for p from our known total lighting demand:

45 = 365*(8p + 16p + (16 * 4 / 6)p)

p = 0.003556375TWh = 3.556375GWh

So this guesstimate tells us that every hour we've got a base load lighting usage nationwide in service sector buildings of about 3.6GWh.  Doing this 8 hours a day, 365 days a year would mean a consumption of around 10.3TWh each year.  That's a big number - about a quarter of total lighting energy use!

So how do we get wasted energy use down? Unfortunately lighting isn't high on the list of priorities for some companies, despite them ending up spending hundreds, thousands or even millions of pounds on the energy it consumes.  Their accountants look at the capital costs of changing lighting systems and if the pay back period is more than a couple of years, it gets passed over. Heck, some retailers even have a problem with closing the doors in the Winter!

Another problem is that many service sector companies are tenants, and often energy use is lumped into a standard service charge.  The building managers.owners have no impetus to reduce energy use as the service charge covers their expenditure, whilst the tenants may be unaware of what fraction of the ever increasing service charge is due to energy use and what is due to other constantly increasing costs such water supply, sewerage or insurance.  This is not only an issue for how we encourage businesses to become more energy efficient, but also whether we can persuade them to invest in micro-generation technologies as well - tenants often can't and owners don't see the need to.

Of course as energy prices continue to rise, the pay back periods for installing smarter lighting systems and profits to be made from reducing or turning off extraneous lights will improve, so hopefully we'll have more companies taking notice of the lights the have on in the middle of the night.  And we can carry on nagging organisations that we work for or shop at to cut down on the obvious energy wastes such as pointless lighting.  After all we all paying for it somehow.

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