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  • The sun was humankind’s first source of power, and, with a little work, may be the

  • last one well ever need. A good desert collects more solar energy in six hours than

  • the entire world uses in a year. The surface area of my body is about, uh, a meter and

  • a half squared. If I laid out in the sun all day long every day for a year, I would collect

  • about 1,500 watts of solar energy. And check it out, pretty much all of the power that

  • we as humans use originally was solar power. And all coal is is the fossilized remains

  • of plants and animals that died eons ago and have been buried in the earth, and they got

  • their energy from the sun. Natural gas and oil, same thing, the sun. Nuclear power, which

  • produces about 20% of our power, is one of the two sources that we have that isn’t

  • originally solar power, the other being tidal, which is created by the moon. Hydroelectric

  • power, how does that water get up in the mountains so that it has to run down the rivers, well,

  • it gets evaporated from the ocean by the sun. Wind power, as you may have guessed by now,

  • all weather on our planet is created by the sun. Burning tree and cornhusks and other

  • bio-mass, which we do in bio-mass powerplants, all of those organisms originally got their

  • power from our sun. And then, we have direct solar power, which yes, gets its energy from

  • the sun and skips all those middlemen. And so it must be more efficient, right? Well,

  • it turns out, it is more efficient, and you’d think that being more efficient, it would

  • be less expensive, unfortunately, it is not. When we think about solar power, generally

  • what we think of is photovoltaic cells, those big blue panels that people put on their roofs

  • to generate electricity. When I was researching this, I was actually surprised to find weve

  • known about the photoelectric effect for almost 200 years. It was discovered in 1839 by a

  • 19 year old kid named Edmund Becquerel. Now, I have to totally go on a tangent here because

  • this is really interesting. Edmund Becquerel is part of what we call a scientific dynasty.

  • So Edmund Becquerel discovered the photoelectric effect. His father discovered that you can

  • refine ores into their pure metals using electrolysis, and his son, along with Marie and Pierre Curie,

  • discovered radioactivity. It’s just interesting to me that there can be that much scientific

  • talent generation from generation in one family. It’s like Martin and Charlie Sheen, except

  • with science and actually cool. Anyway, the most efficient solar cells that we have tend

  • to find their way into outer space, because efficiency is expensive, but it doesn’t

  • matter how expensive something is when youre dealing with the International Space Station,

  • cause it’s not like you can run a wire up to it. The International Space Station

  • has 16 115ft. long solar wings. All combined, at peak, these solar panels produce 120 kilowatts

  • of electricity, which, is a lot. And now I can tell just by looking into your eyes that

  • youve been filled with an insatiable desire to know more about photovoltaic panels. So

  • if you hit a wafer of polysilicon with light, some of the electrons on that silicon will

  • get knocked off and theyll be free electrons. Now, this is something that’s normal, but

  • it’s not anything like the amount of power that you would need to create a solar panel.

  • But what scientists and engineers figured out is that if you dope the silicon, and that’s

  • a technical term, it just means lacing it with impurities, if you dope the silicon with

  • phosphorus, it suddenly has way too many electrons, and then you get what we call N-type silicon,

  • ‘N’ because it’s negative. And then if you take another wafer of silicon, and

  • you dope it with boron, that doesn’t have enough electrons, and so you get P-type silicon,

  • forpositive’. A traditional solar panel is just a layer of N-type silicon sandwiched

  • on top of a layer of P-type silicon, and then connected with a conductor, which we call

  • a wire. Stick something on top of that wire and you can power it with a solar panel, and

  • depending on the size of that panel, it could be a calculator, a house, or a frickin

  • space station. The trick is, how do we either get solar panels to be so efficient that they

  • can make up for their high costs, or find new, less expensive materials, that we can

  • use to create photovoltaic panels. Now I have to get off topic a little bit here and talk

  • about how solar power has an advantage that not a lot of people think about. In general,

  • when we produce power as humanity, we do it at giant power stations that are often hundreds

  • of miles away from where the power is actually used. In order to get the power from the power

  • station to your house, you have to put it on these giant transmission lines, which are

  • extremely expensive and also, having the power travel all that distance is pretty inefficient.

  • You can lose as much as 30% of the power that you generate just getting it from one place

  • to another, which, frankly, is embarrassing. We created all those mega-tons of carbon dioxide

  • just so we can lose the power when were distributing it. And there’s a reason we

  • do that, and that’s because with a coal-fired power plant, you don’t want to have a bunch

  • of little inefficient ones scattering the landscape, you want to have one big one in

  • one place where you can control the pollution and make it as efficient as possible. But

  • with solar power, you can actually generate the power exactly where youre using it.

  • You can put the panel on your roof and use it in your house. We call itdistributed

  • power’, and it’s great. It does sometimes make sense to use solar power in a centralized

  • fashion, giant fields full of solar panels, especially if those giant fields are in places

  • where the sun shines 364 days a year. But don’t get too excited, despite marvelous

  • efficiency of distributed power, solar panels still remain much more expensive than centralized

  • power stations. Photovoltaic panels now blanket rooftops all over the world, but while they

  • make ecologic sense, they still don’t make economic sense. Getting a good value for your

  • dollar from a solar panel is pretty much impossible which is why were still so reliant on coal

  • and natural gas for most of our electricity. To this day, we get more power from burning

  • wood than we do from the solar panels. So youre saying to yourself, there’s got

  • to be a better way to do this. And maybe there is. If you were a particularly malevolent

  • or scientifically-minded child, you may have experimented with this technique in the past,

  • using your magnifying glass to create power, and you were probably using that power to

  • kill small insects, which is not something I condone, but there you have it. Sunlight

  • carries a lot of energy, and if you concentrate it into one place, you can do a lot of work

  • and I prefer if we would be using that work to push electrons into your house so you can

  • watch me on your computer screen, not to use it so you can vaporize small animals. Lenses

  • like this are far too expensive to use in solar power plants, so instead, we use mirrors.

  • These are called concentrating solar power plants, and in general, what’s done is we

  • use the mirrors to focus light on a single point, and there’s two real ways that it’s

  • done. One, you build a giant tower, and then you fill a field with mirrors, and you make

  • sure that the mirrors are always focusing the sun on the top of that tower. Now, as

  • you might expect, building a giant tower that can handle being heated to some ridiculous

  • heat is kind of expensive, but it is cheaper than pure photovoltaic. The other way that

  • concentrated solar power works is that theyll build giant mirrored troughs, like parabolic

  • sort of half-cylinders, and in the middle of those, theyll put a pipe, so by the

  • time the oil is finished traveling through this parabolic trough, it is so hot that as

  • soon as it enters a vat of water, the water immediately vaporizes, and that’s generally

  • how powerplants work, you vaporize water and the vapor takes up much more space than the

  • liquid and so there’s a tremendous amount of pressure and they use that pressure to

  • drive a turbine, which creates electricity. But even with all that fancy engineering,

  • concentrated solar power plants still, in the best of circumstances, only produce power

  • at about 11 cents per kilowatt-hour, which is about twice as much as a natural gas powerplant.

  • But wait a minute, now weve got two solar solutions. One, photovoltaics where the capture

  • of the energy is the most expensive part, and two, concentrated solar power, where the

  • conversion of the energy into electricity is the most expensive part. What if we could

  • have both of these technologies, and have the best of both worlds? Well, it turns out

  • that we can, and it may just be the one solution that allows solar power to become cost-effective

  • in our energy market. By using really sophisticated photovoltaic cells that can take in far more

  • power than the one in your calculator, engineers and scientists are using mirrors to concentrate

  • light on very small photovoltaic cells. Now, mirrors, which are actually capturing the

  • light, are 10 times bigger than the solar panel, and thus the solar panel is taking

  • in 10 times more sunlight and producing 10 times more energy, but the solar panel itself,

  • the expensive part, stays the same size. Using this technique, which we callconcentrated

  • photovoltaics’, we get the most cost-effective form of solar power that we currently have

  • on the market today. They call itCPV’, forconcentrated photovoltaics’, and

  • there are several gigawatts of it getting ready to go online in the next 10 years or

  • so. It’s important to note that a gigawatt is a lot of electricity, that’s about as

  • much as produced by the largest nuclear powerplants in America. Going back to the Space Station

  • for a moment, mostly just because I want to show more of the awesome graphics of the Space

  • Station, as I said before, it doesn’t matter how expensive the panels on the Space Station

  • are, ‘cause there’s no other way to get power up there. Now when I said that those

  • solar panels create about 120 kilowatts of electricity, I was kind of lying to you. About

  • half the time, the panels on the Space Station are producing 0 watts of power, and that’s

  • because it’s in the shadow of the Earth. And here on Earth, when were standing here,

  • we call that shadownight time’, and it is the nemesis of solar power. And so unfortunately

  • it would seem that solar power could never satisfy 100% of our energy needs. Well

  • always need something else, whether it’s coal or nuclear or natural gas, to keep the

  • lights on at night. Unless, of course, we could find some way to store the power up

  • during the day and then let it all loose at night. Well, turns out, we kinda can. We can

  • pump it up hills and then during the night, let the water fall down through turbines generating

  • electricity. Or we can pressurize giant closed caverns in the Earth to thousands of PSI during

  • the day, let the air escape to generate electricity. We can heat salt until it melts, and then

  • use the molten salt to boil water at night. Or we can use the solar power during the day

  • to split water into hydrogen and oxygen, and then use the hydrogen in fuel cells to generate

  • power at night. But unfortunately, solar power is obviously already really expensive, and

  • each one of these solutions to store that power adds to the price. So while it’s feasible

  • and we have created the solutions, implementing them is just not in the near term. In physics,

  • we have a thing called the Law of Conservation of Energy, which says that you can’t get

  • more out of a system than you put in. Well, in economics, there might as well be a Law

  • of Conservation of Dollars, which says that people aren’t going to put more in than

  • they have to in order to get a certain amount of work done. Why would I climb over a mountain

  • if someone’s already built a tunnel through it? i mean, aside from the obvious fact that

  • that tunnel releases hundreds of megatons of carbon dioxide and other pollution into

  • the atmosphere every single year. Meanwhile, the biggest powerplants in America produce

  • around 1,000 megawatts of electricity. If we had 116 billion of those, it would be just

  • enough to match the amount of power that the sun shines down on our little planet every

  • single day. I’m Hank Green, solar power is awesome,

  • and I hope you learned something.

The sun was humankind’s first source of power, and, with a little work, may be the

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Solar Energy

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    Bing-Je posted on 2013/12/06
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