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TEDxWarwick

David MacKay: A reality check on renewables

March 12, 2012

How much land mass would renewables need to power a nation like the UK? An entire country's worth. In this pragmatic talk, David MacKay tours the basic mathematics that show worrying limitations on our sustainable energy options and explains why we should pursue them anyway. (Filmed at TEDxWarwick.)

David MacKay - Professor
As an information theorist and computer scientist, David MacKay uses hard math to assess our renewable energy options. Full bio

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Double-click the English subtitles below to play the video.
When the Industrial Revolution started,
00:15
the amount of carbon sitting underneath
00:18
Britain in the form of coal was as big as the amount
00:20
of carbon sitting under Saudi Arabia in the form of oil,
00:23
and this carbon powered the Industrial Revolution,
00:28
it put the "Great" in Great Britain,
00:31
and led to Britain's temporary world domination.
00:32
And then, in 1918, coal production in Britain peaked,
00:37
and has declined ever since.
00:41
In due course, Britain started using oil and gas
00:43
from the North Sea, and in the year 2000,
00:46
oil and gas production from the North Sea
00:49
also peaked, and they're now on the decline.
00:52
These observations about the finiteness of
00:57
easily accessible, local, secure fossil fuels,
01:00
this is a motivation for saying, "Well, what's next?
01:03
What is life after fossil fuels going to be like?
01:07
Shouldn't we be thinking hard about
01:10
how to get off fossil fuels?"
01:12
Another motivation, of course, is climate change.
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And when people talk about life after fossil fuels
01:17
and climate change action, I think there's a lot of
01:19
fluff, a lot of greenwash, a lot of misleading advertising,
01:23
and I feel a duty as a physicist to try to
01:27
guide people around the claptrap and help people
01:30
understand the actions that really make a difference
01:32
and to focus on ideas that do add up.
01:35
Let me illustrate this with what physicists call
01:40
a back-of-envelope calculation.
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We love back-of-envelope calculations.
01:45
You ask a question, you write down some numbers,
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and you get yourself an answer.
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It may not be very accurate, but it may make you say,
01:50
"Hmm."
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So here's a question: Imagine if
01:53
we said, "Oh yes, we can get off fossil fuels.
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We'll use biofuels. Problem solved.
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Transport, we don't need oil anymore."
01:59
Well, what if we grew the biofuels for a road
02:02
on the grass verge at the edge of the road?
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How wide would the verge have to be for that to work out?
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Okay, so let's put in some numbers.
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Let's have our cars go at 60 miles per hour.
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Let's say they do 30 miles per gallon.
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That's the European average for new cars.
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Let's say the productivity of biofuel plantations
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is 1,200 litres of biofuel per hectare per year.
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That's true of European biofuels.
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And let's imagine the cars are spaced 80 meters
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apart from each other, and they're just perpetually going
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along this road.
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The length of the road doesn't matter, because the longer
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the road, the more biofuel plantation we've got.
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What do we do with these numbers?
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Well, you take the first number, and you divide by
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the other three, and you get eight kilometers.
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And that's the answer.
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That's how wide the plantation would have to be,
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given these assumptions.
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And maybe that makes you say, "Hmm.
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Maybe this isn't going to be quite so easy."
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And it might make you think, perhaps there's an issue
03:03
to do with areas, and in this talk,
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I'd like to talk about land areas, and ask,
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is there an issue about areas? The answer is going to be
03:11
yes but it depends which country you are in.
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So let's start in the United Kingdom,
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since that's where we are today.
03:20
The energy consumption of the United Kingdom,
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the total energy consumption, not just transport, but everything,
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I like to quantify it in light bulbs.
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It's as if we've all got 125 light bulbs on all the time,
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125 kilowatt-hours per day per person
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is the energy consumption of the U.K.
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So there's 40 light bulbs' worth for transport,
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40 light bulbs' worth for heating,
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and 40 light bulbs' worth for making electricity,
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and other things are relatively small
03:49
compared to those three big fish.
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It's actually a bigger footprint if we take into account
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the embodied energy in the stuff we import
03:56
into our country as well, and 90 percent of this energy today
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still comes from fossil fuels, and 10 percent only
04:02
from other, greener -- possibly greener -- sources
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like nuclear power and renewables.
04:07
So,
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that's the U.K., and the population density of the U.K.
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is 250 people per square kilometer,
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and I'm now going to show you other countries
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by these same two measures.
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On the vertical axis, I'm going to show you
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how much light bulbs -- what our energy consumption
04:24
per person is, and we're at 125 light bulbs per person,
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and that little blue dot there is showing you the land area
04:30
of the United Kingdom,
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and the population density is on the horizontal axis,
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and we're 250 people per square kilometer.
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Let's add European countries in blue,
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and you can see there's quite a variety.
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I should emphasize, both of these axes
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are logarithmic. As you go from one gray bar
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to the next gray bar you're going up a factor of 10.
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Next, let's add Asia in red,
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the Middle East and North Africa in green,
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sub-Saharan Africa in blue,
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black is South America,
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purple is Central America,
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and then in pukey-yellow, we have North America,
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Australia and New Zealand.
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And you can see the great diversity of population densities
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and of per capita consumptions.
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Countries are different from each other.
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Top left, we have Canada and Australia, with enormous
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land areas, very high per capita consumption,
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200 or 300 light bulbs per person,
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and very low population densities.
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Top right, Bahrain has the same energy consumption
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per person, roughly, as Canada,
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over 300 light bulbs per person,
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but their population density is a factor of 300 times greater,
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1,000 people per square kilometer.
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Bottom right, Bangladesh has the same population density
05:47
as Bahrain but consumes 100 times less per person.
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Bottom left, well, there's no one.
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But there used to be a whole load of people.
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Here's another message from this diagram.
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I've added on little blue tails behind Sudan, Libya,
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China, India, Bangladesh.
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That's 15 years of progress.
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Where were they 15 years ago, and where are they now?
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And the message is, most countries are going to the right,
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and they're going up,
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up and to the right -- bigger population density
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and higher per capita consumption.
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So, we may be off in the top right-hand corner,
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slightly unusual, the United Kingdom accompanied by
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Germany, Japan, South Korea, the Netherlands,
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and a bunch of other slightly odd countries,
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but many other countries are coming up
06:31
and to the right to come and join us,
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so we're a picture, if you like, of what the future energy
06:35
consumption might be looking like in other countries too.
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And I've also added in this diagram now some pink lines
06:43
that go down and to the right.
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Those are lines of equal power consumption
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per unit area, which I measure in watts per square meter.
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So, for example, the middle line there,
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0.1 watts per square meter, is the energy consumption
06:56
per unit area of Saudi Arabia, Norway, Mexico in purple,
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and Bangladesh 15 years ago,
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and half of the world's population lives in countries
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that are already above that line.
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The United Kingdom is consuming 1.25
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watts per square meter.
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So's Germany, and Japan is consuming a bit more.
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So, let's now
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say why this is relevant. Why is it relevant?
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Well, we can measure renewables in the same units
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and other forms of power production in the same units,
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and renewables is one of the leading ideas for
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how we could get off our 90 percent fossil fuel habit.
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So here come some renewables.
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Energy crops deliver half a watt per square meter
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in European climates.
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What does that mean? And you might have anticipated
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that result, given what I told you about the biofuel plantation
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a moment ago.
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Well, we consume 1.25 watts per square meter.
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What this means is, even if you covered
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the whole of the United Kingdom with energy crops,
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you couldn't match today's energy consumption.
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Wind power produces a bit more,
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2.5 watts per square meter, but that's only twice as big
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as 1.25 watts per square meter,
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so that means if you wanted literally to produce total
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energy consumption in all forms on average from
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wind farms, you need wind farms half the area of the U.K.
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I've got data to back up all these assertions, by the way.
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Next, let's look at solar power.
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Solar panels, when you put them on a roof,
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deliver about 20 watts per square meter in England.
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If you really want to get a lot from solar panels,
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you need to adopt the traditional Bavarian farming method
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where you leap off the roof and coat the countryside
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with solar panels too.
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Solar parks, because of the gaps between the panels,
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deliver less. They deliver about 5 watts
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per square meter of land area.
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And here's a solar park in Vermont with real data
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delivering 4.2 watts per square meter.
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Remember where we are, 1.25 watts per square meter,
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wind farms 2.5, solar parks about five.
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So, whatever, whichever of those renewables you pick,
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the message is, whatever mix of those renewables
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you're using, if you want to power the U.K. on them,
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you're going to need to cover something like
09:19
20 percent or 25 percent of the country
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with those renewables.
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And I'm not saying that's a bad idea.
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We just need to understand the numbers.
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I'm absolutely not anti-renewables. I love renewables.
09:29
But I'm also pro-arithmetic. (Laughter)
09:31
Concentrating solar power in deserts delivers
09:36
larger powers per unit area, because you don't have
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the problem of clouds,
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and so this facility delivers 14 watts per square meter,
09:42
this one 10 watts per square meter,
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and this one in Spain 5 watts per square meter.
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Being generous to concentrating solar power,
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I think it's perfect credible it could deliver 20 watts
09:52
per square meter. So that's nice.
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Of course, Britain doesn't have any deserts.
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Yet. (Laughter)
10:00
So here's a summary so far.
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All renewables, much as I love them, are diffuse.
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They all have a small power per unit area,
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and we have to live with that fact.
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And that means, if you do want renewables
10:13
to make a substantial difference for a country like
10:16
the United Kingdom on the scale of today's consumption,
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you need to be imagining renewable facilities
10:22
that are country-sized, not the entire country
10:24
but a fraction of the country, a substantial fraction.
10:28
There are other options for generating power as well
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which don't involve fossil fuels.
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So there's nuclear power, and on this Ordnance
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Survey map, you can see there's a Sizewell B
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inside a blue square kilometer.
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That's one gigawatt in a square kilometer,
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which works out to 1,000 watts per square meter.
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So by this particular metric, nuclear power
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isn't as intrusive as renewables.
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Of course, other metrics matter too, and nuclear power
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has all sorts of popularity problems.
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But the same goes for renewables as well.
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Here's a photograph of a consultation exercise in full swing
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in the little town of Penicuik just outside Edinburgh,
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and you can see the children of Penicuik celebrating
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the burning of the effigy of the windmill.
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So people are anti-everything, and we've got to keep
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all the options on the table.
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What can a country like the U.K. do on the supply side?
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Well, the options are, I'd say, these three:
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power renewables, and recognizing that they need to be
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close to country-sized; other people's renewables,
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so we could go back and talk very politely to the people
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in the top left-hand side of the diagram and say,
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"Uh, we don't want renewables in our backyard,
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but, um, please could we put them in yours instead?"
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And that's a serious option.
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It's a way for the world to handle this issue.
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So countries like Australia, Russia, Libya, Kazakhstan,
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could be our best friends for renewable production.
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And a third option is nuclear power.
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So that's some supply side options.
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In addition to the supply levers that we can push,
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and remember, we need large amounts,
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because at the moment,
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we get 90 percent of our energy from fossil fuels.
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In addition to those levers, we could talk about other ways
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of solving this issue, namely, we could reduce demand,
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and that means reducing population
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— I'm not sure how to do that —
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or reducing per capita consumption.
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So let's talk about three more big levers
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that could really help on the consumption side.
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First, transport. Here are the physics principles that tell you
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how to reduce the energy consumption of transport,
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and people often say, "Oh, yes, technology can answer everything.
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We can make vehicles that are a hundred times more
12:36
efficient." And that's almost true. Let me show you.
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The energy consumption of this typical tank here
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is 80 kilowatt-hours per hundred person kilometers.
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That's the average European car.
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Eighty kilowatt-hours. Can we make something a hundred times
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better by applying those physics principles I just listed?
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Yes. Here it is. It's the bicycle. It's 80 times better in energy
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consumption, and it's powered by biofuel, by Weetabix.
13:02
(Laughter)
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And there are other options in between, because maybe
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the lady in the tank would say, "No, no, no,
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that's a lifestyle change. Don't change my lifestyle, please."
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So, well, we could persuade her to get into a train,
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and that's still a lot more efficient than a car,
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but that might be a lifestyle change,
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or there's the eco-car, top-left.
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It comfortably accommodates one teenager
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and it's shorter than a traffic cone,
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and it's almost as efficient as a bicycle
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as long as you drive it at 15 miles per hour.
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In between, perhaps some more realistic options
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on this lever, transport lever, are electric vehicles,
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so electric bikes and electric cars in the middle,
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perhaps four times as energy efficient
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as the standard petrol-powered tank.
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Next, there's the heating lever.
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Heating is a third of our energy consumption in Britain,
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and quite a lot of that is going into homes
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and other buildings doing space heating and water heating.
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So here's a typical crappy British house.
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It's my house, with the Ferrari out front.
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What can we do to it?
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Well, the laws of physics are written up there,
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which describe what -- how the power consumption
14:05
for heating is driven by the things you can control.
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The things you can control are the temperature difference
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between the inside and the outside, and there's this
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remarkable technology called a thermostat.
14:17
You grasp it, you rotate it to the left,
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and your energy consumption in the home will decrease.
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I've tried it. It works. Some people call it a lifestyle change.
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You can also get the fluff men in to reduce the leakiness
14:28
of your building -- put fluff in the walls, fluff in the roof,
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and a new front door and so forth,
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and the sad truth is, this will save you money.
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That's not sad, that's good, but the sad truth is, it'll only
14:40
get about 25 percent of the leakiness of your building,
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if you do these things, which are good ideas.
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If you really want to get a bit closer to Swedish
14:49
building standards with a crappy house like this,
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you need to be putting external insulation on the building
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as shown by this block of flats in London.
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You can also deliver heat more efficiently using heat pumps
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which use a smaller bit of high grade energy like electricity
15:04
to move heat from your garden into your house.
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The third demand side option I want to talk about,
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the third way to reduce energy consumption is,
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read your meters.
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And people talk a lot about smart meters,
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but you can do it yourself.
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Use your own eyes and be smart, read your meter,
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and if you're anything like me, it'll change your life.
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Here's a graph I made.
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I was writing a book about sustainable energy,
15:27
and a friend asked me, "Well how much energy do you use
15:30
at home?" And I was embarrassed. I didn't actually know.
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And so I started reading the meter every week,
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and the old meter readings are shown
15:36
in the top half of the graph, and then 2007
15:39
is shown in green at the bottom, and that was when
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I was reading the meter every week, and my life changed,
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because I started doing experiments and seeing
15:45
what made a difference, and my gas consumption
15:49
plummeted because I started tinkering
15:51
with the thermostat and the timing on the heating system,
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and I knocked more than a half off my gas bills.
15:54
There's a similar story for my electricity consumption,
15:56
where switching off the DVD players, the stereos,
16:00
the computer peripherals that were on all the time,
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and just switching them on when I needed them,
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knocked another third off my electricity bills too.
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So we need a plan that adds up, and I've described for you
16:13
six big levers, and we need big action because we get
16:15
90 percent of our energy from fossil fuels,
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and so you need to push hard on most if not all of these levers.
16:21
And most of these levers have popularity problems,
16:26
and if there is a lever you don't like the use of,
16:28
well please do bear in mind that means you need
16:32
even stronger effort on the other levers.
16:34
So I'm a strong advocate of having grown-up conversations
16:38
that are based on numbers and facts, and I want to close
16:41
with this map that just visualizes for you
16:45
the requirement of land and so forth in order to get
16:47
just 16 light bulbs per person
16:52
from four of the big possible sources.
16:54
So, if you wanted to get 16 light bulbs, remember,
16:57
today our total energy consumption is 125 light bulbs' worth.
17:01
If you wanted 16 from wind, this map visualizes a solution
17:05
for the U.K. It's got 160 wind farms,
17:09
each 100 square kilometers in size,
17:11
and that would be a twentyfold increase
17:14
over today's amount of wind.
17:16
Nuclear power, to get 16 light bulbs per person, you'd need
17:18
two gigawatts at each of the purple dots on the map.
17:21
That's a fourfold increase
17:24
over today's levels of nuclear power.
17:25
Biomass, to get 16 light bulbs per person, you'd need
17:29
a land area something like three and a half Wales' worth,
17:32
either in our country, or in someone else's country,
17:36
possibly Ireland, possibly somewhere else. (Laughter)
17:39
And a fourth supply side option, concentrating solar power
17:42
in other people's deserts,
17:45
if you wanted to get 16 light bulbs' worth,
17:47
then we're talking about these eight hexagons
17:49
down at the bottom right.
17:53
The total area of those hexagons
17:54
is two Greater London's worth of someone else's Sahara,
17:56
and you'll need power lines all the way across Spain
18:01
and France to bring the power from the Sahara to Surrey.
18:02
We need a plan that adds up.
18:08
We need to stop shouting and start talking,
18:11
and if we can have a grown-up conversation,
18:15
make a plan that adds up and get building,
18:19
maybe this low-carbon revolution
18:22
will actually be fun. Thank you very much for listening.
18:23
(Applause)
18:25
Translator:Joseph Geni
Reviewer:Morton Bast

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David MacKay - Professor
As an information theorist and computer scientist, David MacKay uses hard math to assess our renewable energy options.

Why you should listen

David MacKay is a professor of Natural Philosophy in the Physics department at the University of Cambridge and chief scientific adviser to the UK Department of Energy and Climate Change. He received a degree in Experimental and Theoretical Physics from Trinity College and a PhD. in Computation and Neural Systems as a Fulbright Scholar at Caltech. In 1992, MacKay was made the Royal Society Smithson Research Fellow at Darwin College at University of Cambridge and was elected a Fellow of the Royal Society in May 2009. He has also taught at the African Institute for Mathematical Sciences in Cape Town. In 2003, his book Information Theory, Inference, and Learning Algorithms was published and, in 2008, he self-published Sustainable Energy — Without the Hot Air. Both books are fully available for free online.

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