Four simple actions

I wrote an article, "We need a plan that adds up", for The Guardian and publicservice.co.uk. For the Grauniad I also created a new graphic which I thought I would show here.

Four simple actions that make significant energy savings, and one that doesn't.
The left-hand column shows five contributors to the average energy consumption of a typical reasonably-affluent Guardian reader. The right-hand column shows the reduced consumption, post-action.
Any comments? Would the figure work better if I put the phone charger in the middle instead of at the bottom of the list?

Man on radio

BBC Radio 4 has a programme called More or Less, all about numbers. On 24 April 2009 the programme opened with a conversation between me and Tim Harford, talking about energy numbers. Tim likes the book (in fact he likes it so much that he gets its name wrong!) After me, he talks to a lady from the Sustainable Development Commission who graciously dismisses my book for being full of big equations and too technical. Or something. Can anyone understand what she's on about?
If you are quick, you can listen to the podcast.
I also wrote an article for the BBC website, 'Saving the planet by numbers'.

Hot Air Oscars nomination: A Clean Use for Australian Coal

Australian Minister for Resources and Energy, Martin Ferguson, is hereby nominated for the Hot Air Oscar for highest-impact use of the words 'clean', 'ultra-clean', and 'low emissions'.


"This technology unlocks energy from Australia's significant stranded and uneconomic coal reserves."
"Technologies that convert coal and gas to ultra-clean diesel and jet fuel have the potential to replace Australia's declining oil reserves."
"The Australian Government is encouraging the development of coal-to-liquids in Australia through its election commitment to use the $500 million National Low Emissions Coal Fund to support projects generating minimal carbon emissions which utilise our extensive coal resources."


In a nutshell, they're investing government money in turning uneconomic coal that would otherwise have been left in the ground into CO₂ in the atmosphere. Brilliant! Icebergs all round!

Thanks to Alexander Ac for the nomination.

Man holding bulb

On youtube, there is a new video, arranged by the University of Cambridge, featuring someone not unrelated to me, holding a lightbulb and talking about energy plans. Hope you enjoy it! It took three days of filming to make it.

[In case the youtube video goes missing, here is the University's 'Cambridge Ideas' page.]

Every little hurts - Hot Air Oscars

There is
a superb article on Greenwash by Ed Gillespie.

Buy eco-lights, get free air miles.

Wow, Tesco has to be a strong contender for the Hot Air Oscar for best consumer-engagement

Hot Air Oscars nomination: Eco Friendly Mobile Phone Charger

Thank you to Pierre Joly for nominating The Plug In And Go Green Eco Charger for the Hot Air Oscar for Best Use of the "if-everyone" Multiplying Machine. If you've read Sustainable Energy - without the hot air or my page on phone-chargers left on standby, you'll know how thrilled I am to learn that
"The Eco Charger reduces the amount of energy needed to power a mobile phone more than any other on the market."
Fantastic news. If everyone got one of these, the ad says, the UK "could make a collective saving as a country of £85 million" (assuming, incidentally, an electricity price of 28.5p per kWh... Shurely a bit high?!).
Unfortunately the CarPhone Warehouse didn't have the space in their advertisement to apply the "if-everyone" multiplier to the price tag, but the Hot Air Oscars column is happy to help out: If everyone in the UK bought one of these "Eco Chargers" (at £22.99), it would cost us, as a country, £1.3 billion.

Greenbird wind-powered car - brilliant!

British engineering breaks wind-powered land-speed record. Wow!

Hot air Oscars nomination: most useless invention

Nick Cook has nominated the EDF Energy ideal home show, Alex Hort, and the University of Plymouth for a Hot air Oscar for "An ingenious idea that recovers useful energy from a drain pipe". "Rain water descending a down pipe is captured and stored behind an internal 'dam'... Each rush of water turns a small, plastic turbine... providing electricity which is stored in rechargeable batteries."
The raw power of rainwater on a roof of area 40 square metres, rainfall 584 mm per year, with a drainpipe of length 6 metres, is 0.001 kWh per day. This is less than one ten-thousandth of the average British person's electricity consumption. The economic value of the power captured by this contraption is roughly 5 pence per year. The energy cost of making the system and inserting it into a drainpipe must be many times greater than the energy it would ever give back.

Display energy certificates - a missed opportunity to communicate

UK legislation requires that many large buildings display a certificate, updated every few months, that shows "how efficiently the building is being used".

This mandatory certificate could have been used to communicate information to people, and to engage the building's users in the challenge of improving the building's energy consumption. However, it seems to me that the designers of the certificate have almost completely blown it: the certificate's main features looks fairly colourful, but they convey amazingly close to no information at all.

How much information can be conveyed on a sheet of paper? One of the simplest principles of communication is that the message should depend on something; the message should not be fixed in advance. For example, Lord Nelson, at sea, had a collection of a few dozen flags from which he could select some to run up his mast. Which ones he ran up his mast depended on what message he was intending to communicate. Someone looking at Nelson's ship would not know in advance what the flags would look like.

This communication principle is almost entirely lost from Display energy certificates: the look of the certificate is almost entirely determined and fixed before any building data are collected.


The most prominent feature of the certificate is the "A-to-G" scale, with its green-to-red/brown colour scheme. Almost all the numbers on this scale are fixed; the only adjustable piece is the little arrow that points at "how well this building is being used". This performance is measured in meaningless pseudo-units, with "100" corresponding to "average for buildings of this type". This number can't be compared, from building to building, since two buildings might be of different types, and the certificate doesn't say anything about the type. Nor can an ordinary person work out what the number means, nor what they should do about it, because the number can be computed only by experts using the government-approved software that churns out these certificates. (I've looked on government websites, and have been unable to find any definition of the magic formula for computing the number; I imagine I would have to pay to attend a government-sanctioned course in Display energy certificate cookery.)



The second feature of the certificate is the top-right blue rectangle. Again, this object achieves amazingly little communication. It is meant to show how much CO2 the building's use is emitting. I would like to make a prediction: I predict that, on the first certificates displayed in the year 2009 in all the thousands of buildings across the country, every single certificate will have a blue rectangle of exactly the same height!. I make this prediction because it looks to me as if the government-sanctioned standardized software auto-scales the entire blue rectangle so that it has got a standard size! Therefore the only way to find out the CO2 emissions of the building is to look really closely at the scale of the graph, which shows, in the smallest font conceivable, an absurdly long number, at the top of the vertical axis, partly overlapping the axis. This absurdly long number, I would guess, is the actual CO2 emissions. In my photo I think it shows 26095 tonnes of CO2 per year. If someone ever manages to read this number (please bring a magnifying glass!), will it mean anything to them? Is a typewritten number a good way to convey information? Is it a good idea to show five decimal places of precision? When communicators discuss how to label the axes of a graph, does anyone recommend that the six tics on the graph should be labelled (nothing), (8693), (nothing), (17396), (nothing), and (26095)?

The one interesting fact that is well conveyed by the blue rectangle is the breakdown of CO2 emissions between electricity and heating: the top (light) half of the blue rectangle shows the electricity contribution, and the lower (dark) half shows the heating.





And finally, the third prominent colour element in the display is the "Previous operational rating" graph (bottom right, orange), which shows "how efficiently energy has been used in this building over the last three accounting periods". At present (in early 2009), this colour object conveys no information at all as it shows only a repeat of the energy performance rating displayed on the left-hand side. In due course, maybe it will reveal an interesting trend, but it will depend on the choice of "accounting period". Is the accounting period going to be one year? If so, the comparison of last year with the year before will be meaningful, but is it going to engage users? Imagine if, every day when you entered your building during 2009, the porter informed you what the total energy consumption had been in 2007 and 2008. Would these facts interest you in putting effort into efficiency drives? I fear that a yearly update is too long a timescale for any useful engagement to happen. On the other hand, if the "accounting period" lasts, say three months, then the variation in operational rating from quarter to quarter would be entirely dominated by seasonal effects. My guess is that the certificates will be updated annually, so building-users will become completely blind to the certificate. The opportunity for user engagement is almost entirely lost.

What have we seen so far?

1. the main colourful numbers are in meaningless units. As it says, "the numbers do not represent actual units of energy consumed; they represent comparative energy efficiency. 100 would be typical for this kind of building."
2. the CO2 emissions are displayed in meaningful units, but these numbers are not displayed in a way that an ordinary person can understand.




Does the certificate have any useful information on it? Yes, hidden away in tiny print at the bottom left hand side are interesting numbers - at least to building energy specialists. The "technical information" shows, in a table, the energy use (heating and electrical), expressed in the meaningful units of kWh per square metre per year. And to make this energy use comprehensible, the table also specifies the "typical use" (of buildings "like this", I presume).

What could have been done better? As far as I can tell, the entire piece of paper is really conveying just two numbers:

`this building's heating consumption is: 519 kWh/m2/y';
`this building's electrical consumption is: 249 kWh/m2/y'.

The certificate hides these two numbers in the technical corner, displays some unknown munging of them on to the A-to-G scale, displays their effective carbon-ratio in the blue rectangle, and shows how the total changed compared to earlier years.

How could the certificate be better? Well, it could have been better in two ways:

1. the certificate could display the two numbers that it is meant to communicate more clearly, more accessibly, more meaningfully, and more educationally.
2. the certificate could communicate more than two numbers.

Let me spell out what I mean.

1. the certificate could display the two numbers that it is meant to communicate more clearly, more accessibly, more meaningfully, and more educationally. For example, the energy consumption (per square metre) could be displayed visually on a scale that shows the energy consumptions of a bunch of other real buildings - so as to help people visualize and aspire. Looking at the current A-to-G scale, someone in a "D"-performing building may well ask "does any building like mine ever get an A or even a B?" They don't know if it is at all plausible. If energy consumption were compared with that of benchmark buildings (eg, Whitehall, the Swiss Re tower, Freda's flower shop, Cambridge University Library, BedZed), then people would see what is possible, and could get a message such as "my building is as bad as Whitehall!" or "we're using 20 times as much as BedZed." Given real comparative data, people could aspire to meaningful goals.
2. the certificate could communicate more than two numbers. For example, there could be a duty to display and compare energy consumption every month or every week (for at least some number of consecutive weeks per year). Then the regularly-updated certificate could engage building-users in the challenge of energy-saving. If someone tries an energy-saving action, they need to get feedback within a week to tell them whether it made a difference. Without rapid feedback, no-one will be interested in energy saving ideas.

PS - To see the whole certificate in one image, follow this link

Uncontrollable burning coal-waste-heap

People often emphasize the role of uncontrolled accidental burning of fossil fuels in backward parts of the world.
I grew up in a part of the developing world called the Potteries, near the middle of England. The Potteries were rich in clay and coal, and one hill near Keele village was stuffed with little coal mines when I was a child. There were rich thick seams very close to the surface. These photos and google satellite maps show what's left there now: a great pile of rubble that is perpetually on fire. It looks rather like a Hollywood movie's improbable view of medieval England, in which every slope somehow has smoke scudding across it.

Eco super hero

Great to see that colleges are training people to be eco heroes, installing HEAT PUMPS and SOLAR THERMAL SYSTEMS!! Brilliant news.

Designers with a conscience

Graphic designers for good - looks like a useful community of people to tap into! They don't just want to promote useless consumerist tat.

Even more wind power per unit area

This is my third post giving factual data about the power per unit land area of wind farms in Britain. My first post described a farm near the coast made of small machines (27m diameter); the power per unit area was 1.4 W/m². The second post cherry-picked the best windfarm in Britain (located in Shetland); the power per unit area was 6.5 W/m². The turbines there have diameter about 50m. Now returning from mid-ocean, let's ask "what do really big land-based turbines deliver?" I picked the Glass Moor windfarm, which has eight 2 MW machines, each with a diameter 82m. (It's the biggest windfarm close to Cambridge; no special cherry-picking, here.) Looking at the OS map, I judged the area occupied by the windfarm to be 2 km². Based on one year's data, the average output of this windfarm (per unit land area) is 2.2 W/m².
These data support the view that 2 W/m² is a good ballpark figure for the power per unit area of a modern windfarm in England.

Climate-change inactivism

I enjoyed reading John Mashey on how science works, and how to critically read scientific claims such as those made by climate-change inactivists. From there, I found my way to his equally interesting analysis of Bjorn Lomborg's motivations. I actually rather like Bjorn Lomborg and don't think he's the antichrist that many make him out to be; but it is interesting to read John Mashey's analysis of the political effect of Bjorn Lomborg's arguments. In a nutshell, Lomborg's recent writings have said "yes, global warming (X) is a priority, but not as high a priority as 'A' and 'B'", where John Mashey reckons A (Eg, give lots of money to the developing world to fix things there) has been chosen not because Lomborg really wants to devote effort to A, but rather because he knows these sort of aid donations won't happen, so putting them top of a list of priorities is a good way of persuading people not to do lower things in the list (X). The space in the list between A and X is padded out with other items ("B") (eg, open up free trade more) that the neo-cons would be happy to see happen. Interesting analysis.
Myself, I had a different take on Lomborg, which is that he genuinely does care, and wants us to choose numerate policies that work; and that he comes to different conclusions from some of us simply because he tacitly chose a different objective from what we might have chosen. Specifically, the objective in his recent books seems to be something like "human economic welfare between now and the year 2100". I'd love to sit down with Lomborg and discuss what he thinks the optimal investments would be if the objective were changed to "planet still functioning well at supporting human life in the years 2200, 2500, and 3000".
I've tried to converse with Lomborg but sadly I think he's too busy being famous now.

Hot Air Oscars: Recyclemania and Eastern Washington University dining services

I'm happy to announce the launch of the first annual "Hot Air Oscars".
These awards go to the person or organization who (in the judgment of the panel) best exemplify the modern-day survival skills of greenwash and twaddle-emission. There will be awards for "most misleading advertising", for "best use of magic playing fields", for "best doublespeak", for "most creative use of the word 'zero'", for "best bogus comparison", for "best speaking with many faces", for "best supporting liar", for "best inflated difference", and for "best conparison".
Nominations may be sent to David MacKay. Shortlisted achievements will be featured on this blog over the next month or two. The winners of the Hot Air Oscars will be announced in mid 2009.

Opening nominations...
The first nomination in the "best green spin" category is the fine attempt by David McKay [no relation], director of dining services at Eastern Washington University (EWU), and Paul Kyle, associate director of dining services, to put a positive spin on their decision to use disposable Styrofoam plates and bowls in the cafeteria. "Our goal is to lessen the amount of BODs [organic pollutants in water] by washing fewer dishes," said Kyle; "The use of Styrofoam plates and bowls is an excellent energy source for the waste-to-energy plant," said McKay.
or to put it another way, Styrofoam plates are great because you can just throw them away and burn them. They claim that this initiative somehow ties in with a local initiative called Recyclemania.

I am sure the environment is thanking them for their efforts, but not everyone is so supportive. Laci Hubbard, president of the Eastern Environmental Club, said that while the group is pleased that Dining Services has been supportive of ... Recyclemania, they are "concerned about the move to use additional Styrofoam products and the logic of their subsequent explanation for why Styrofoam is a better choice for the environment."

Please keep the nominations rolling in. The judges will be happy to consider new categories for the Hot Air Oscars.

More windfarm power per unit area

Executive summary:
The windfarm with the highest load factor in the British Isles has a power per unit area of 6.5 W per square metre.

Background:
Commentors on my previous article on
the power per unit area of windfarms queried whether any cherry-picking might have happened
in the selection of Blood Hill windfarm; it was also suggested that we should work out the numbers for Burradale, the famous windfarm in Shetland with the highest load factor in Britain. The answer to the first query is "no, not at all" - Blood Hill was selected at random, and as I said, I would encourage anyone who can be bothered to look up the data for other windfarms to do so and add the results to the "withouthotair" wiki.
And now, to satisfy the request for cherry-picked facts about wind in the UK, I am happy to present...

The data: Burradale has five wind turbines: three in "phase 1" and two in "phase 2". Their capacities are 660 kW and 850 kW respectively, and their average outputs over the last few years have been 357 kW and 446 kW respectively. (That corresponds to load factors of 52% and 54%.) I judged the "area occupied" by the five turbines to be 0.3 square kilometres. The average power per unit area of this windfarm is 6.5 W per square metre.

This number can be compared with my assumed figure of 2 W per square metre for typical onshore windfarms in the UK.

So, a cracking good place for wind, Shetland! What does it need? Obviously what this place really needs is a campaign group opposed to expanding wind farms in Shetland. And The Good Lord hath provided "Sustainable Shetland".

Power per unit land area of windfarms

As I've said in SEWTHA (the book), the average power per unit land area of a typical well-located onshore windfarm in Britain is about 2 watts per square metre. (Or 2 MW per square km.) This number is my estimate of the best that can be done in Britain, and, as I explained in the appendix, the theoretical power per unit land area doesn't depend very much on the size of the turbines used, because bigger turbines are spaced further apart.

I'm always keen to check my numbers and update them if necessary. Today the the New Scientist interview with James Lovelock prompted me to write a blog article giving explicit data from a real windfarm. James Lovelock says "to spoil all the decent countryside in the UK with wind farms is driving me mad. It's absolutely unnecessary, and it takes 2500 square kilometres to produce a gigawatt - that's an awful lot of countryside." That's a power per unit area of 0.4 W/m², which is 5 times smaller than my 'best possible' 2 W/m² estimate.

Let's look at some data. I picked a random windfarm in Britain with ten 27m-diameter turbines: Blood Hill windfarm. The helpful REF website gives exact energy-generation statistics for several years. The collage at the top of this page shows the data, and a map of the site, which is very close to the sea in Norfolk. What's the area of this site? The blue grid lines are 1km squares. I'd say the ten turbines 'occupy' about 0.3 km² (including an appropriate strip of land around the turbines, where similar size turbines could not be placed). The average output of the ten turbines is 420 kW. So that is a power per unit area of 1.4 W/m².

If anyone would like to repeat this calculation for real data from other windfarms around Britain or the world, we could collate the answers in the open-source wiki for Sustainable Energy - without the hot air.

Google searches, energy cost, carbon footprint, and cups of tea

A friend asked me to confirm or deny the assertion (Harvard/BBC) that two Google searches on a desktop computer produces 14g of CO2, which is the roughly the equivalent of boiling an electric kettle.

• ``US physicist Alex Wissner-Gross claims that a typical Google search on a desktop computer produces about 7g CO2.
  
• ``However, these figures were disputed by Google, who say a typical search produced only 0.2g of carbon dioxide.''
  

My own rough back of envelope guess came out in between Wissner-Gross's assertion and Google's...

Here's how I worked it out:

1. according to a google search(!), google has about 700,000 servers.
   
2. let's guesstimate the power to run a server and all its plumbing: 250 W.
   
3. google received 90 million searches per day in 2006
   and 1200 million per day in 2007...
   
4. Hmm, this growth rate is big enough that it is going to be hard to get a trustworthy answer!
   
5. Well, let's multiply 700,000 servers * 0.250 kW * 24 hours per day / 1200 M searches per day -
   that is 0.0035 kWh per search; 0.007 kWh for a pair of searches; and 3.5g of CO₂ for a pair of searches. (Assuming that electricity has a footprint of 500 g per kWh.) [In fact I think I heard that google has lots of servers in Iceland, where the electricity footprint is much smaller.] Meanwhile, boiling a 250 ml cup of water uses about 0.028 kWh. So my estimate is that the energy cost of two google searches (measured at the googleplex alone) is about one quarter of the energy cost of boiling a cup.
   

This calculation has not included the energy cost of running your own desktop computer, wireless, and modem for the duration of the search too; nor the cost of running the internet twixt you and google. If it takes you one minute of computer time to do the search, and if your computer and peripherals use 120 W, then the cost of your computer's power in that duration is 0.120 kW * (1/60) hour, which is an extra 0.002 kWh.
Here's the bottom line from my rough guesses: the total energy cost of the pair of searches seems to be about 0.01 kWh. That's exactly the same as the energy used by leaving a phone charger plugged in for one day. Which is also the same as the energy used by driving an average car for one second.

Would electric freight vehicles be possible?

In Sustainable Energy - without the hot air, one of my main conclusions is "electrify everything" - in particular, I recommend electric vehicles. At a recent talk, someone in the audience said, yes, maybe electric cars are now viable. But surely you couldn't electrify freight? Leaving aside two possible answers (namely 1: for local freight deliveries, electric trucks are already genuinely in use, and are manufactured by a couple of companies in the UK; 2: we could make electric freight like eletric trolley buses, using overhead lines), I thought it would be interesting to investigate, using the same model I used for cars in my book, the possibility of making long-distance freight vehicles with on-board batteries.
The model assumes that energy goes into air resistance, into rolling resistance, and into brakes. The model includes regenerative brakes (assumed to be 50% efficient, round-trip), and includes energy inefficiency in the energy-conversion chains (from grid to battery and from battery to wheels). The frontal area is assumed to be 8.6 m² and the freight carried is 26 tons. The other main assumptions are the distance between stops (500m? 5000m?) and the typical speed (50km/h? 100km/h?).

The figures above and below show the theoretical energy consumption (in kWh per ton-km) for two different batteries' energy densities (corresponding to lead acid and lithium), compared with a fossil fuel truck with the same frontal area and load, versus the range (ie the distance between refuelling stops). The top figure is for the case of 500 m distance twixt stops and 50 km/h speed. The bottom figure (just above) is for the case of 5000 m twixt stops and 100 km/h speed.
The bigger the battery, the bigger the range and the bigger the energy consumption. The main conclusion of these figures is that, on energy grounds, trucks with big batteries are viable. They are superior in energy consumption to the fossil fuel truck. (The point at the top, by the way, is the fossil fuel truck benchmark from the book, which is obtained from government statistics; the lower point is the theoretical performance of a fossil fuel truck according to the model. The latter is presumably lower because the former includes a load of empty-running journeys.)
Of course many other factors need to be borne in mind - could a truck stop provide a 120-kW outlet for charging each truck parked at the truck stop, for example? And what is the capital cost of the batteries? And could they be recycled?
But I find it interesting that in principle, long-distance electric trucks would be more energy-efficient than fossil-fuel trucks. As usual, I have declared one unit of grid electricity to have the same value as one unit of chemical energy. Yes, yes, with today's electricity mix in Britain, blah blah blah, inefficiencies in conversion, ... a factor of 2.4 or some such... But as usual I am focussing attention on the future energy system we should be building, not the details of today's obsolete fossil-fuel electricity system. We want to electrify transport in order to get the whole energy system off fossil fuels as much as possible.

The FCX Clarity from Honda

On this week's Top Gear, James May called the FCX Clarity "the most important car for 100 years".
[Photo courtesy of automobiles.honda.com.] It runs on hydrogen, which "will never run out", because it is "the most abundant element in the universe". And the only emissions are water.
What twaddle!
The programme took the time to point out that the electricity to power a Tesla electric car in Britain is produced at a fossil fuel power station. Why didn't they also discuss where the hydrogen comes from?
Top Gear loves to quantify accelerations, lap times, car prices, top speeds - why couldn't they quantify the energy requirements to run "the car of the future", the FCX Clarity? And compare it with the Tesla?
Here's the answers, according to chapter 20 of Sustainable Energy - without the hot air.

The energy consumption of the FCX Clarity is 69 kWh per 100 km. (Very similar to the consumption of an ordinary fossil fuel car.) That's assuming the hydrogen is produced in the standard way, using lots of methane and a bit of electricity, and counting one unit of chemical energy as having the same energy content as one unit of electricity. Meanwhile, the energy consumption of the Tesla (according to its manufacturers) is 15 kWh per 100 km. (Of electrical energy.) Even if we penalize electricity, saying "every 1 kWh of electricity costs 2.5 kWh of fossil fuels", the Tesla is still much better than the fuel-cell car, and better than the average fossil fuel car. (And in the future, we won't be getting electricity from fossil fuels, hopefully!)
So the hydrogen car is NOT a "solution" to our problem, if our fundamental problem is an energy problem.

Why on-site renewables don't add up

Straight up, I want to say I love renewables, and I believe that we should have a massive increase in renewables as part of making a sustainable energy plan that adds up (as explained in my book Sustainable Energy - without the hot air, now available on paper).
This is an article about on-site renewables. Imagine a developer is making a new urban development. Offices or homes, perhaps. A three-floor building. Under some planning regulations, new buildings must get some fraction of their energy consumption from on-site renewables. Now, these regulations have some undeniable benefits: if it is expensive to install on-site renewables, the developer may modify the building so as to reduce its energy consumption, thus making it less costly to reach the required renewable fraction. Having local renewable energy production may also increase awareness about energy consumption among the building's users. And some local renewables are no-brainers - making hot water using solar panels, for example, makes complete sense, providing roughly half of the hot water consumption of an average home.
But here is the problem:

200 kWh per year per square metre = 23 W per square metre

On the left, 200 kWh per year per square metre is the typical total energy consumption of many homes and offices, expressed as energy per year per square metre of floor area. In terms of energy rating bands, 200 kWh/y/m² is the boundary between bands F and G. Many government buildings use twice as much as this. (The Home Office uses 400 kWh/y/m², for example.) The Passivhaus standard, at 120 kWh/y/m², is not much better than this 200 kWh/y/m² benchmark.
On the right, I've converted this quantity into watts per square metre, which are the unit in which I prefer to express renewable power production. Sadly, most renewables have powers per unit land area that are substantially less than 23 W per square metre. Wind farms generate 2 W/m². Energy crops generate 0.5 W/m². Solar photovoltaic panels generate 20 W/m². And remember, we're imagining a three-floor building. So the power required per unit land area occupied by the building is not 23, but 3x23 = 69 W/m².
On-site renewables are an interesting gesture, but if we are serious about renewables making a big contribution, they have to be big - they must occupy a land area much bigger than the land occupied by the buildings we are powering. If you want to completely power a three-floor 200 kWh/y/m² building from energy crops and wood, for example, then the land area required for the energy crops and wood must be roughly 140 times as big as the land footprint of the building.
The response of an angry green campaigner to what I have just written can be predicted: "But we could make the buildings far more efficient!" Could we? I'd love us to build more-efficient buildings, but show me data. Not wishful thinking, but NUMBERS. The Elizabeth Fry building at UEA is often held up as an example of a state-of-the-art eco-friendly building. And here are the numbers for that building (from page 299 of my book). It consumes 96 kWh/y/m², which is 11 W/m², which is only about 50% better than the Energy-Rating-Band-F/G benchmark from which I started.
The bottom line: if you want to completely power a typical building, or even an amazing eco-building, from renewables, most of those renewables have to be offsite. There isn't room on-site! And it's probably a better use of resources to accept this fact up front, rather than force developers to squeeze uneconomic figleafs (such as micro-turbines) into their developments. We should modify the planning regulations for new buildings so that developers are still required to build renewables, but are encouraged to build new renewable capacity off-site.

Petrol, diesel, miles per gallon, litres per 100 km, energy, and emissions

Too many units! Too many things to measure! In Europe they talk about "the one litre car" (using 1 litre of fuel per 100 km). In Britain, drivers of the Prius are happy to do "more than 50 miles per gallon". In the USA, gallons are different. Then there's emissions (does it emit less than 100 grams of CO₂ per km?) and finally there's energy measures (for example, the average British car consumes 80 kWh per 100 km).

And, while we're dealing with all these different units, the most annoying detail of all is that petrol is different from diesel. Diesel has bigger energy per litre (roughly 10% more), and it has bigger carbon emissions per litre too.

I've put together a graph that makes it possible to compare and convert some of these measures of vehicle performance.



Some memorable anchors on this diagram:

1. A 90 mpg petrol vehicle is roughly equivalent (in energy and emissions) to a 100 mpg diesel car. Both use an energy of about 30 kWh per 100 km and have emissions of about 75 g per km. People have sometimes lampooned the Prius for consuming more fuel than a BMW. If the Prius is using petrol and the BMW is using diesel, then it's not fair to compare the numbers of litres used.
2. A 'one litre car' delivers 282 mpg, and uses about 10 kWh per 100 km. This is the energy consumption, incidentally, of quite a few prototype electric cars (measured at the socket).
   
3. My 'average UK car today' uses 80 kWh per 100km and emits 200 g per km. Europeans would call it an 8-litre car.

For more about energy consumption of eletric vehicles and hydrogen vehicles, see Sustainable Energy - without the hot air.
Small print: 'mpg' means miles per imperial gallon. 'g' means grams of carbon dioxide.
Energy contents (high heat values) and emissions were assumed to be:
Petrol: 34.7 MJ per litre; 2344 g per litre.
Diesel: 37.9 MJ per litre; 2682 g per litre.

Good article on 'green electricity'.

I always lampoon 'green electricity tariffs' in my lectures. The Grauniad published a good article on them yesterday. Key points: the electricity companies sell some MWh of 'green' electricity multiple times; and the big power generation companies are falling way below the fraction of green electricity that they are meant to produce under the subsidy scheme.

How to boil water

A friend told me he'd been fighting with his kitchen-cohabitants over the question of whether to simply use the gas to make hot water for pasta, or whether to use the kettle, then put it in the pot.
To answer this question quantitatively, I did some experiments and I've written a new webpage, How much is inside HOT WATER? The page assumes that the motivation is to save energy. The conclusions apply to Britain today and to similar countries.

My conclusion is that using the gas hob is slightly better in energy terms than using the kettle; but my recommended behaviour depends on the time of year. In the winter, if you would like to have more heat in your kitchen, then using the gas hob alone is definitely best; in the heat of summer, using the kettle may be preferable.

Disclaimers, small print...
If your motivation is to save money then the answer will depend on your fuel prices. If your motivation is to cook the pasta as fast as possible then you should use neither method alone - you should use both the kettle and the hob, with roughly half in each.

Lights on cars in the daylight

According to the Dail Mail, crazy European legislation forcing car drivers to keep headlights on ALL day could inflate fuel costs by up to £160 a year.

What are the numbers? Well, this is one that I worked out earlier. It's in chapter 9 of Sustainable Energy - without the hot air, on page 58. Let's say the four bulbs for the running lights on a car use about 100 W. Allowing for the engine's and generator's inefficiencies, this 100 W of bulb power requires a petrol power of 730 W. For comparison, the petrol consumption of an average car running along at 50 km/h and consuming one litre per 12km is 42000 W. So having the lights on while driving requires 2% extra power.

If you drive 50km per day and fuel costs £1.20 per litre then you spend £5 per day on fuel. Putting the lights on is going to increase your costs by 2%, which is 10p per day. That's £37 pounds per year, for a typical driver. Obviously the answers come out differently if we change the vehicle to a Hummer, or if we replace the incandescent bulbs by modern LEDs.

I hope this helps!

The book's finished!

I'm happy to announce that Sustainable Energy - without the hot air is finished.
It's got a publisher, a cover design, and a publication date of December 1st 2008.
All that remains is some frantic last minute editing and correcting; then an 8-week wait.
The book will remain free on my website.

Performance data for a GWiz in London

This article is by Kele Baker and David MacKay, based on data collected by Kele

The performance of the G-Wiz varies with driving conditions and the weather. The G-Wiz can be driven on 'high' or 'low' power. The lights may be on or off. And the efficiency of the battery appears to depend on the temperature. The graph shows data for 19 charging events: the distance travelled in miles is on the horizontal axis and the energy required from the grid to recharge the battery (measured at the socket with a Maplin meter) is on the vertical axis.

The best performance was 16 kWh per 100 km. The worst was 33 kWh per 100 km. The average was 21 kWh per 100 km. This number is roughly four times better than the energy consumption of an average petrol car doing 33 miles per gallon, which uses 80 kWh per 100 km. In money terms, the electricity cost of the G-Wiz is 2.1 pence per km (assuming 10 p per kWh).

Mysterious cheap electricity generated in Nevada

There is a strange violation of economics going on on the Nellis Solar Power Plant wikipedia page. It asserts that the US air force are paying 2.2 c per kWh for electricity from a solar PV farm that happens to be on their land. This sounds far too cheap. The article says the '14MW' farm cost $100M to build (that's 7 dollars per watt, peak) and will generate 25M kWh per year. That means it will generate an income of $0.55M per year for the owners of the farm (who paid $100M, remember). That corresponds to a pay-back time of 180 years. So what's going on? Is it a strange Nevada phenomenon? Did aliens subsidise the farm? Or did wikipedia get the numbers wrong?