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.

Monday, 2 April 2012

Powering Down Loughborough: Energy Descent Plan Part 1

One of the things that many Transition Town groups across the planet have done is start to draw up "energy descent" plans. These are documents that look at how much energy a town is using, what potential it has to generate cleaner energy itself and then it gives some more concrete targets for energy reduction programmes (insulation, unnecessary energy use, etc).

I've been thinking a bit about how we'd tackle that in Loughborough on and off over the last year or so, and I brain dumped what I'd come up with on the Transition Loughborough mailing list last summer, to little discussion. I've been thinking more about this again recently, especially with the recent panic in the UK about fuel strikes and several nuclear power station plans being dropped by the commercial groups that were developing them. I thought it was about time I revisited this and cast the net for comments a bit wider than the somewhat closed Transition Loughborough Google Group. This post is thus an updated version of the posting I made last summer with a few revisions and updates thrown in.

To get the ball rolling, I thought I'd just look at electricity use to start with. Of course there's also oil used in transport, gas used for cooking/heating and the use of fossil fuel derived non-fuel products (plastics, fertilizers, etc), but I had to start somewhere and electricity seemed tractable for finding numbers, making some estimates, etc.

First off I wanted to "guestimate" what the current electricity usage in Loughborough is. Unfortunately there's not a big kWh meter attached to the pylons that stride over Loughborough Moor, so I had to do a bit of research and number crunching. Here's some figures I've nabbed from various sources:

  • Loughborough population - 57,600 people (source: Wikipedia/Charnwood BC),
  • Average UK per capita electricity consumption: 6106kWh (source: World Bank via Google's Public Data Explorer. This covers both domestic use and each person's share of commercial/industrial electricity usage). 
Sticking to our combined domestic/commercial/industrial figures means that we can guesstimate that Loughborough has an annual electrical energy usage of:

57600 x 6106 = 351705600kWh = 351705.6MWh = 351.7056GWh

If we divide this by the number of hours in a year, we'll get the average power:

351705600 / (365 x 24) = 40149.04109589kW

Lets call that 40MW to be nice and round, especially as the population and per capita electricity usage figures come from different years. This is the average requirement - peaks in demand will be higher. Conveniently, the National Grid total typical consumption is 40GW across the whole country, with peaks up to 60GW, so we could expect that Loughborough might need to have generating capacity up to 60MW on hand if the ratio is similar to the nation as a whole.

What I was wondering was what renewable energy sources we could deploy in and around the town to meet this demand. If we could do more than required then groovy, we're looking good for a local energy generation plan. If we can't meet this demand we'll need to look at what can be shaved off and/or rely on "external" power generation from the National Grid (off shore wind, hydro, nuclear, etc. If we're aiming for a low carbon/post-Peak Oil target we'll want to reduce/remove the demand for fossil fuel based generation as well obviously, so we'd rather not have oil/coal/gas fired stations in the mix).

My first thought was Wind Power. The BWEA/DTi wind speed trackers say that Loughborough gets just under 6m/s average winds at 45m above ground level in a variety of locations around the town. Not a great wind speed, so possibly marginal for deployment of large scale turbines. Brush Electrical did plan to build one behind their plant in Loughborough a few years ago to demonstrate some of their generators but I don't think anything came of it. The University has a small (kW scale) wind turbine that's used for research purposes and there's one or two medium sized turbines on farms around the town. So wind probably isn't our first choice for electricity generation, although if push comes to shove we might be able to squeeze a few turbines in... lets say six of those big 1MW turbines on Loughborough moors to the east of the town and on the high ground about the M1 to the south west of the town. So 6MW at most of wind as a very rough estimate. Good old Wikipedia tells us that:

1 MW turbine with a capacity factor of 35% will not produce 8,760 MWh in a year (1 × 24 × 365), but only 1 × 0.35 × 24 × 365 = 3,066 MWh, averaging to 0.35 MW.

So our six 1MW large turbines will produce 18396MWh = 18.396GWh per year

OK, what about solar PV? To work out what capacity we could have if everyone suddenly got keen on solar panels (and could afford them) I took a two pronged approach: considering first the domestic roof space available, and then the industrial roof space. I didn't want to look at ground based "solar farm" set ups as I didn't want to "waste" potential food or biomass producing land under solar panels.

For domestic roof space, I got an estimate of the number houses and flats in Loughborough from of 21,108. Now I'm not going to sit looking at Google maps to work out which of these 21,108 properties could have solar panels and how big the arrays can be. Instead I'm going to estimate that a quarter of them will be facing south east to south west and of those about half again would be suitable for PV panels (not in conservation areas, enough roof space, roof capable of taking the loading, etc):

21108 x 0.25 x 0.5 = 2638.5 suitable properties.

Now domestic PV installations seem to range in size from less that 1KWp to over 5KWp, but most seem to average out at around 2.5KWp so I'm going to use that as a ball park figure. This means that I reckon if we had enough PV panels and willing folk to stump up the cash, we could get:

2638.5 x 2.5 = 6596.25 KWp of solar PV.

Call it 6.500MWp in round numbers.

For industrial roof space I took a slightly different tack: on Google maps satellite view I measured one of the University's large buildings to be roughly 50m x 100m. A square metre of solar PV can generate about 150Wp, so a 50m x 100m roof covered in PV panels should be able to generate up to:

50 x 100 x 150 = 750000Wp = 750KWp

Lets half that to account for parts of sloping roofs that face north, have existing services on them, skylights, etc to give us 375KWp per large roof. Then I took at look on Google maps and did a rough "finger in the air" guesstimate at how many other large industrial buildings looked to be roughly the same size (or multiples thereof in some cases). I reckoned there was about 40 such buildings in Loughborough, so large industrial buildings should give us:

40 x 375 = 15000KWp = 15MWp

Combining the domestic and commercial solar PV we get 21.5MWp. Note that this is MW _peak_: this is the maximum power output that you'd get under tip top sunshine. We'll get a lot less than that on average in the UK - English Heritage reckon that a 2KWp array on a house will generate about 1.5MWh over an average UK year. That means that our combined 21.5MWp of solar would generate:

21.5 x 1500 x (1000 / 2) = 16125000KWh = 16125MWh = 16.125GWh per year

There are other renewable options available but their contribution is likely to end up being a couple of megawatts at most. I'm thinking anaerobic digestion plants running small combined heat and power plants. Farmers already have these, but they already use the energy themselves. We'd be looking at additional biomass, such as power from the sewerage plant. Even if we took all the poop from the 57600 inhabitants of the town and assume that it had 50% of around 2500KCal (10 MJ or 0.0029075KWh) dietary intake left after digestion and we could turn 20% of that remaining energy into electricity, we'd end up with:

57600 x 0.0029075 x 0.5 x 0.2 = 16.7472KWh per day
= 6112.728KWh per year

Combining the total solar PV output with our wind and AD output gives:

18.396GWh + 16.125GWh + 0.006112GWh = 34.527GWh

Lets be generous again and call it 35GWh per year. So solar PV, wind and AD of human poop combined are only going to handle about a tenth of the 351.7056GWh demand we currently have. And that's before we take into account folk who want to move from use of liquid fossil fuels in transport to electric traction. Even if my rough estimates are half of what they should be (ie I've over looked a load of usable roof space or we could get lots more wind working around the area than I assumed), we've still got a big gap to make up.

To me this is saying that we need to both massively reduce our per capita demand, and still have access to large scale centralised power sources on the Grid (large off shore wind farms, nuclear stations, etc) in addition to the decentralised renewables generation. Reduction in demand is going to be mean turning devices off, using lower power equipment, no longer illuminating the outsides of buildings to try to make them look pretty, not lighting empty fourth floor office spaces at 1am, turning off some street lights, etc. Of course if EVs or hydrogen power for transport start to take off, the demand for electricity will start rising rapidly, wiping out lots of these potential savings and still leaving us with an energy gap.