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On the longer term, it's a bit more 
daunting. 

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Longer term meaning now to the year 2100.

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Things change naturally in that 
amount of time. 

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The fact that we have to come up with 
some 

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new energy supply by the year 2100 doesn't 
sound all that frightening. 

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It sounds like an interesting 
challenge. 

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The problem is that if 

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you use a scenario predictor 

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like the Kaya identity module that you've 
played with, and ask how much 

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carbon-free energy would it take by the year 2100 
to continue 

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growth as we have been growing and yet not 
melt down the climate, 

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it turns out that we have to come up with 
something like 20 terawatts of 

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energy by the year 2100. 

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For comparison, we are generating about 
13 terawatts of energy today,

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not carbon free. 
This 20 terawatts has to be carbon free. 

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And it turns out that most of these things 
that make up wedges 

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you couldn't possibly scale them up to 
come up with this much energy. 

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If you were going to do it using nuclear 
power, 

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for example, you'd have to build a 

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couple of power plants a 
week for the next 100 years. 

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You would make thousands of nuclear power 
plants. 

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You just can't scale it up. 

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And so, looking for ideas that could scale 
up to this kind of carbon 

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free energy is something of a challenge, 

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but I've heard some really cool ideas 
discussed. 

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One of them that I like is to put solar 
cells on the moon. 

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You could also have solar cells in 
orbit around the Earth, 

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but then you'd have to lift the solar 
cells out of Earth's gravity. 

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Whereas, if you could manufacture them on 
the 

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moon you could make them out of lunar 
soil. 

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And so you wouldn't necessarily have to 
bring all the 

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00:02:01,530 --> 00:02:04,540 
mass of those solar panels up to the 
moon. 

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00:02:04,540 --> 00:02:08,570 
Of course, there's no clouds on the moon, 
there's no dust blowing around, 

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so it would be a perfect environment for 
capturing sunlight. 

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And the question is getting the 
energy back to earth. 

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Which could be done, by using
microwave radiation,

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00:02:19,590 --> 00:02:21,140 
beaming energy it back to Earth. 

40 
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It's not as inefficient as you might 
think. 

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00:02:23,480 --> 00:02:27,490 
Maybe half of the energy that gets sent 
here could be collected there. 

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And this technology, it's claimed, could 
scale up to 

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00:02:31,490 --> 00:02:33,730 
that amount of energy by the end of the 
century. 

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It would be a big project. 
But, we have decades to do it. 

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00:02:37,880 --> 00:02:42,360 
Another cool idea I heard was high 
altitude windmills. 

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00:02:42,360 --> 00:02:46,810 
Windmills at the ground are limited in 
their power by the intensity of the wind. 

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But if you get up into the jet stream, the 
wind is blowing much faster. 

48 
00:02:50,590 --> 00:02:53,730 
If you get too high up, the air gets too 
thin and then it loses its ability 

49 
00:02:53,730 --> 00:02:55,470 
to turn a propeller, so there's an 

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00:02:55,470 --> 00:02:59,220 
optimum altitude where the power density 
is the highest. 

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00:02:59,220 --> 00:03:05,060 
You could build windmills that would 
fly like like giant bat kites,

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00:03:05,060 --> 00:03:07,730 
tethered to the ground by a conducting 
cable,

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00:03:07,730 --> 00:03:11,120 
which would would harvest energy from 
the jet stream. 

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00:03:11,120 --> 00:03:14,320 
And this, it is claimed, could also scale 
up. 

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00:03:14,320 --> 00:03:20,440 
A third option is less less exotic, but 
solar thermal 

56 
00:03:20,440 --> 00:03:24,380 
energy is also said to be scalable. 
This is where you use 

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00:03:24,380 --> 00:03:30,060 
some a focusing set of mirrors to 
concentrate 

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00:03:30,060 --> 00:03:35,310 
the sunlight on a little pipe of 
water where you generate steam. 

59 
00:03:35,310 --> 00:03:38,560 
And then you send the steam to a turbine 
to generate electricity, just 

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the same as you would if you had a coal 
power plant instead. 

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On the time frames of the next 
century 

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we have a bold new challenge that we have 

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to rise to.