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Speaker 1: Get in touch with technology with tech Stuff from how

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Speaker 1: stuff Works dot com. Hey, everybody, welcome to tech Stuff.

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Speaker 1: I'm Jonathan Strickland. I am your host. I'm an executive

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Speaker 1: producer with How Stuff Works in my Heart Radio, and

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Speaker 1: I love all things tech and uh. I'm currently on vacation, y'all.

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Speaker 1: And because I'm on vacation for a couple of weeks

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Speaker 1: out in sunny London and Paris, I thought I would

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Speaker 1: bring some classic episodes to you guys. I didn't want

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Speaker 1: to skip any episode dates, but at the same time,

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Speaker 1: I didn't quite have the time to record a whole

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Speaker 1: bunch of extra episodes. So we're gonna look at some

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Speaker 1: classic episodes in the next few shows, with the exception

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Speaker 1: of the April first show, that will be a brand

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Speaker 1: new episode, so make sure you tune in for that

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Speaker 1: because I recorded something special for April Fool's Day. But

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Speaker 1: today we're gonna take a look back on a classic

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Speaker 1: episode of how solar towers work. This is a method

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Speaker 1: of harnessing energy from the sun, but it's not the

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Speaker 1: same thing as solar panels, which convert solar power directly

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Speaker 1: to electricity. I think it's a pretty fascinating technology, and

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Speaker 1: I talk about how it works and some of the

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Speaker 1: challenges in this episode I hope you enjoy. Today. I

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Speaker 1: want to talk a little bit about solar towers, which

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Speaker 1: is a different way of harnessing the sun's energy, and

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Speaker 1: I think it's a really clever way as well because

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Speaker 1: it doesn't rely on sunlight hitting a panel. Obviously, the

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Speaker 1: big big drawback to that approach is when the sun

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Speaker 1: isn't hitting a panel, you're not generating any electricity, right,

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Speaker 1: So if it's super cloudy or if it's nighttime, if

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Speaker 1: the sun is not able to hit the panel, the

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Speaker 1: sunlight's not getting there, you have nothing to convert into electricity,

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Speaker 1: and your solar panels go on to be unused for

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Speaker 1: that duration. So that can be really rough if you

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Speaker 1: have a long stretch of overcast days, or you live

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Speaker 1: in a place where you don't get solar exposure at

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Speaker 1: your house because of maybe they're taller buildings around you,

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Speaker 1: or trees or whatever. It maybe maybe you have a

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Speaker 1: north facing house rather than a south facing house here

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Speaker 1: in the Northern Hemisphere. If you have a south facing

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Speaker 1: house in the Northern Hemisphere, you're going to get more

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Speaker 1: solar exposure than a north facing house, so solar panels

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Speaker 1: have that drawback. There also, there's efficiency issues with solar panels.

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Speaker 1: When we talk about efficiency, what we mean is how

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Speaker 1: much of the sun's energy can we actually convert into

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Speaker 1: electricity and how much of it do we lose? How

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Speaker 1: much of that energy bounces off the panel and we

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Speaker 1: do not capture it. Most commercial solar panels, the kind

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Speaker 1: that you would put on your house, the efficiencies around eleven,

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Speaker 1: meaning that you're losing a lot of that energy not

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Speaker 1: is not converting into electricity. What that means is that

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Speaker 1: you have to buy more solar panels to cover more space,

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Speaker 1: to collect more solar energy, to generate enough electricity to

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Speaker 1: meet your needs. Obviously, if solar panels were efficient, which

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Speaker 1: is impossible, by the way, physically impossible. People have proved

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Speaker 1: it with mass, then if you if it were a

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Speaker 1: hundred percent efficient, you wouldn't need as many solar panels

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Speaker 1: in order to do what you need to do. That's

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Speaker 1: just not the case in reality. So instead we often

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Speaker 1: have to buy more than what we would like cover

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Speaker 1: a larger area, and even then again you're limited to

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Speaker 1: collecting electricity or generating electricity. I should say during the

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Speaker 1: daylight hours, and electricity also is a use it or

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Speaker 1: lose it kind of thing, meaning that if you don't

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Speaker 1: have an immediate use for that electricity and you don't

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Speaker 1: have a way to store it, you lose that electricity.

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Speaker 1: You have to use it when it's generated, so you

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Speaker 1: need to have some sort of battery system as well,

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Speaker 1: so that in the times when you're not using the

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Speaker 1: electricity you're generating, you can still save it for later use.

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Speaker 1: And until recently, batteries have been really expensive for the home,

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Speaker 1: but Tesla's power wall has kind of led a revolution

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Speaker 1: in that space, and we're starting to see more affordable

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Speaker 1: versions of batteries hit the home market. Okay, all of

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Speaker 1: that's out of the way to just say that the

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Speaker 1: traditional solar panel approach has its drawbacks. Now let's talk

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Speaker 1: about solar towers, because they take a totally different approach

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Speaker 1: to harnessing electricity from the sun and it's really pretty clever,

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Speaker 1: and they can harness electricity or they can generate electricity

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Speaker 1: day or night. So you might wonder, how is that

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Speaker 1: possible when when the Earth rotates so that the sun

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Speaker 1: is no longer shining on a solar tower, where's that

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Speaker 1: electricity coming from. So here's the way it works. Now,

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Speaker 1: I'm largely going to refer to a company called Solar Reserve,

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Speaker 1: which is here in the United States. Solar Reserve is

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Speaker 1: just one company that is building struct is like these

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Speaker 1: around the world, So I don't mean to suggest they're

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Speaker 1: the only one. I'm using them as the example because

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Speaker 1: that so much of their information is available to actually

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Speaker 1: read about and understand. So it's a really helpful approach.

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Speaker 1: Solar towers, Well, first of all, the name kind of

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Speaker 1: gives away the main feature. There's a tower in the

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Speaker 1: center of this uh structure or really multiple structures. So

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Speaker 1: how tall are these towers will according to Solar Reserve,

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Speaker 1: the height of the tower and its thermal receiver. More

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Speaker 1: on that in just a second, tends to be six

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Speaker 1: d forty feet combined or about one. So you've got

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Speaker 1: this tower in a a large area. You want to

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Speaker 1: have an area that gets a lot of solar exposure,

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Speaker 1: otherwise this is not a practical way of generating electricity.

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Speaker 1: So imagine like a desert, nice flat desert, lots of

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Speaker 1: sunlight hitting that desert every typical day, and you have

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Speaker 1: a tower with a receiver on the top of it. Now,

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Speaker 1: that receiver is actually a series of dark panels. And

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Speaker 1: these aren't solar panels, not in the way that you

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Speaker 1: would put on top of your house. They are not

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Speaker 1: converting sunlight into electricity directly. Rather, they are panels that

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Speaker 1: transfer thermal energy. In other words, they're all about transmitting heat.

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Speaker 1: So these panels have sixty six thin wall straight tubes

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Speaker 1: in them. Those tubes are designed to conduct heat from

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Speaker 1: the outside to the inside of that tower. And the

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Speaker 1: tubes are made out of a steel alloy that's covered

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Speaker 1: in a high absorptivity black coating to maximize the amount

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Speaker 1: of energy the panel can absorb. So you've got sunlight

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Speaker 1: shining on this tower, Well, how is that enough to

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Speaker 1: generate electricity on its own. It's not. In fact, what

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Speaker 1: you end up doing is surrounding the tower with mirrors. Now,

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Speaker 1: Solar Reserve uses mirrors that they call heliostats. These helio

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Speaker 1: stats are mounted on arms essentially that allow them to

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Speaker 1: track the motion of the sun. That way, the mirrors

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Speaker 1: maintain the ideal angle to uh to reflect the sun's

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Speaker 1: light directly towards the top of that tower. At that

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Speaker 1: receiving point of the tower. On those panels, and we're

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Speaker 1: talking about a lot of mirrors. Solar Reserve has one

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Speaker 1: area it's called the Crescent Dunes. That's there. There um

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Speaker 1: tower that they have in the US, and the Crescent

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Speaker 1: Dunes towers surrounded by more than ten thousand mirrors covering

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Speaker 1: a fifteen hundred acre field. So this is a big operation.

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Speaker 1: You've got to have a lot of open land for

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Speaker 1: this to work. That's obviously one of the potential drawbacks,

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Speaker 1: right that you need a place that's going to have

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Speaker 1: a lot of solar exposure and you need to have

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Speaker 1: enough space to make it make sense. But assuming you

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Speaker 1: have both of those things, you can do something pretty incredible.

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Speaker 1: I'll have more to say about solar towers in just

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Speaker 1: a second, but first let's take a quick break to

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Speaker 1: thank our sponsor. So what these mirrors do is direct

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Speaker 1: that sunlight up at those dark panels I was talking about.

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Speaker 1: Remember I mentioned there were fourteen. These fourteen panels are

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Speaker 1: divided up into two groups of seven. Each group of

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Speaker 1: seven represents kind of a circuit, and that circuit is

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Speaker 1: not for electricity. It's rather for a circuit of pipes

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Speaker 1: that are circulating liquid salts. So liquid salts are pretty cool, uh,

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Speaker 1: which is a weird way of putting it when you're

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Speaker 1: talking about thermal energy. But liquid salts can hold on

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Speaker 1: to more heat than water can and can remain in

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Speaker 1: liquid form, so in other words, they don't vaporize into steam.

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Speaker 1: And what solar reserve does is it pumps around five thousand,

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Speaker 1: eight hundred gallons of liquid salts per minute through the

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Speaker 1: receiver circuits that run back and forth across the inside

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Speaker 1: of these black panels. So imagine you've got this really

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Speaker 1: tall tower. At the top of the tower, you have

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Speaker 1: these fourteen dark panels, and then let's just take seven

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Speaker 1: on one side. You've got seven of those dark pounds

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Speaker 1: on one side. On the inside of those panels, you

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Speaker 1: would see this criss crossing of a pipe that is

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Speaker 1: circulating liquid salts through the pipe. Heat from the outside

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Speaker 1: comes into the tower and it begins to heat those

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Speaker 1: liquid salts running through that circuit. It's a simple heat transfer.

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Speaker 1: And if you've listened to our podcasts about things like

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Speaker 1: refrigerators and air conditioners, you know about you know how

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Speaker 1: this what the principles are, how how this is based

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Speaker 1: same basic thing. You want to give as much surface area,

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Speaker 1: you know, you want to. You want to dedicate as

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Speaker 1: much surface area as you can to heat and have

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Speaker 1: the liquid salts cross over as much of that surface

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Speaker 1: area as is possible to heat up the liquid salts.

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Speaker 1: As the liquid salts move through the circuit, they become molten,

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Speaker 1: so incredibly high temperatures. So the low side of the

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Speaker 1: temperatures for these liquid salts is five fifty degrees fahrenheit

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Speaker 1: or two degrees celsius. That's the low end. That's that's

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Speaker 1: the chili site. If you want to talk about how

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Speaker 1: hot they get, they can get up to a thousand

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Speaker 1: fifty degrees fahrenheit or five hundred sixty six degrees celsius.

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Speaker 1: That's really impressive. And so you've got this massive amount

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Speaker 1: of stored thermal energy. It's all inside the molten salts.

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Speaker 1: So you've got a lot of heat stored up. What

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Speaker 1: good is heat, Well, you can use heat to do

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Speaker 1: the same thing that is done in power plants all

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Speaker 1: over the world. You use heat to turn water into

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Speaker 1: steam and use the steam to turn a turbine which

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Speaker 1: generates electricity. It's an incredibly simple idea. It's the basis

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Speaker 1: of almost every other type of power plant. With the

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Speaker 1: exception of things like solar panels that are used in

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Speaker 1: solar farms like that, that's generating electricity straight from sunlight,

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Speaker 1: as opposed to using that electricity to somehow turn water

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Speaker 1: into steam. That would be ridiculous. You would lose way

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Speaker 1: too much energy in that approach. But things like coal

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Speaker 1: fired plants, even nuclear power plants, you're talking about generating

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Speaker 1: electricity by heating up water into steam and using that

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Speaker 1: steam to turn a turbine to do work, and that

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Speaker 1: turbine ends up being an electric generator and you get

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Speaker 1: electricity from that. So the the purpose of the solar

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Speaker 1: tower is really just to collect heat. That's it. It's

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Speaker 1: not doing anything magical. It's just generating tons and tons

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Speaker 1: of heat. I know that tons is not really a

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Speaker 1: unit when it comes to heat or temperature, but you

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Speaker 1: understand what I mean. It creates an enormous amount of

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Speaker 1: heat and the molten salts and go into a big

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Speaker 1: storage tank. And it's pretty cool because that storage tank

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Speaker 1: ends up being a a way of holding onto the

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Speaker 1: heat for a long time. According to Solar Reserve, the

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Speaker 1: company says that the molten salt only loses one degree

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Speaker 1: of fahrenheit, or about point five, five, five, etcetera, etcetera

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Speaker 1: degrees celsius in heat per day. So, in other words,

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Speaker 1: if you have a long stretch of overcast days, you

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Speaker 1: still have this massive that really tank. It's not a vat,

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Speaker 1: it's a tank because it's completely enclosed of molten salts

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Speaker 1: and they hold onto that heat, which means you can

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Speaker 1: continuously pump that through your water tank in order to

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Speaker 1: heat water up to steam. And when I say pump,

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Speaker 1: you pump it through. It's a very similar circuit that

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Speaker 1: you would find at the top of the receiver. The

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Speaker 1: molten salts don't mix with the water. Instead, you have

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Speaker 1: a pipe that runs through the water tank. The molten

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Speaker 1: salts run through the pipe and transfer some of their

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Speaker 1: heat to the water through the material of the pipe itself.

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Speaker 1: So you're not laying the molten salts in the water

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Speaker 1: mixed together. That would be ridiculous. Instead, you're having the

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Speaker 1: molten salts move through a pathway, and as they move

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Speaker 1: through that pathway, they heat up the water. The water turns,

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Speaker 1: the steam turns the turbine. Then the steam goes through

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Speaker 1: a condenser to condense the steam back into water, and

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Speaker 1: it goes back into the water tank. So once you

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Speaker 1: use the molten salts to transfer some of this heat,

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Speaker 1: they they've lost that thermal energy. They're now moving into

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Speaker 1: a different tank. It's a tank to pump the liquid

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Speaker 1: salts back up into the top of the tower. So

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Speaker 1: the neat thing with this system is that you can

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Speaker 1: use it to deliver electricity day or night. You've got

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Speaker 1: so much stored heat. After you get the system up

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Speaker 1: and running and it's generated enough molten salt, like it's

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Speaker 1: created enough molten salt through this process to allow this

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Speaker 1: to happen, you can deliver electricity on demand twenty four

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Speaker 1: hours a day. And that's how all power plants work.

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Speaker 1: They deliver electricity on demand. They're not uh set to

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Speaker 1: a certain level, and then if you don't meet that level,

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Speaker 1: they you know, just that electricity goes to waste. They

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Speaker 1: base it upon what the current demand. And I don't

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Speaker 1: mean that as a pun, but it came out of

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Speaker 1: that way. Chris would be so proud. They don't. They

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Speaker 1: respond to whatever the demand is at that time to

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Speaker 1: produce the amount of electricity needed. So super interesting way

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Speaker 1: of doing this by using the sun as an energy

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Speaker 1: source to create the heat needed to turn water into

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Speaker 1: steam and turn a turbine as opposed to a fossil

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Speaker 1: fuel like coal or oil, or a nuclear fuel in

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Speaker 1: the case of nuclear fusion. Now, if we ever are fission,

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Speaker 1: I should say nuclear fission. I know all of you

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Speaker 1: were ready to write in, and you should be because

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Speaker 1: that was a silly mistake I made nuclear fusion. If

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Speaker 1: we ever crack that nut, solar towers may seem quaint

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Speaker 1: in comparison. But that's a very difficult problem in physics

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Speaker 1: to to solve. So we're still waiting on that. I

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Speaker 1: have a little bit more about solar towers to talk about,

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Speaker 1: but before we get there, let's take another quick break.

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Speaker 1: So the neat thing about this, obviously is that if

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Speaker 1: you do have that amount of space, you can really

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Speaker 1: offset a lot of the community's electricity needs with a

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Speaker 1: solar tower. And uh, the company thinks that the lifespan

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Speaker 1: of these solar towers is somewhere in the area of

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Speaker 1: about thirty years, meaning that after thirty years we would

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Speaker 1: have to start to replace parts because just of wear

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Speaker 1: and tear, or they would not be as uh efficient

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Speaker 1: as they had previously been. So, for example, those panels,

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Speaker 1: if the panels become less efficient at transferring heat over time,

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Speaker 1: you would definitely want to reply them because you would

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Speaker 1: be transferring less heat to generate your Your molden salts

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Speaker 1: will be at a lower temperature. It would require more

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Speaker 1: of them to turn water into steam, who become less

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Speaker 1: efficient overall. So you have to make sure that, uh,

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Speaker 1: you're all the parts are working very they're very few

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Speaker 1: moving parts, which is awesome, but you have to make

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Speaker 1: sure they're working throughout the lifetime of the facility and

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Speaker 1: then obviously replaced parts as needed. So the question then

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Speaker 1: becomes doesn't make financial sense to switch over to using

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Speaker 1: solar towers at least to offset electricity generation in a

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Speaker 1: particular area. To answer that question, you have to look

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Speaker 1: at a lot of different factors and it is way

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Speaker 1: more complicated than just a simple yes or no. For

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Speaker 1: one thing, how much solar exposure is the area getting. Obviously,

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Speaker 1: if you're not getting a lot, then that's not going

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Speaker 1: to be a good choice for solar towers or a

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Speaker 1: good place to about a solar tower. I should say

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Speaker 1: also not just where and and you know what time

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Speaker 1: of year do you get solar exposure? Those would be

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Speaker 1: two big things. But how much does electricity cost in

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Speaker 1: that region already. And the reason why you have to

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Speaker 1: ask that question is if you were to provide electricity

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Speaker 1: through the solar reserve system, would it make financial sense

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Speaker 1: to make that switch. If coal is incredibly cheap in

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Speaker 1: the area, then financially it might make more sense to

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Speaker 1: stick with coal, even though we all know there are

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Speaker 1: big environmental drawbacks to using coal. You create a lot

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Speaker 1: of fossil fuels, you have a big carbon footprint that way,

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Speaker 1: but it's hard to argue with the dollar cost of energy.

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Speaker 1: If that dollar cost is higher with solar reserve, that's

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Speaker 1: a tough sell because not everyone is willing to spend

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Speaker 1: more money to keep their homes, uh, you know, supplied

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Speaker 1: with electricity, just so that they have a lower car

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Speaker 1: been footprint with the electricity generation. It's just the truth

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Speaker 1: of the matter, and some people don't have the money

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Speaker 1: to afford the luxury. Obviously, Now, if solar reserve is

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Speaker 1: able to be significantly less expensive than whatever the alternatives are,

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Speaker 1: that's a huge win for solar towers. So it's a

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Speaker 1: lot of different questions along those lines. Obviously, there are

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Speaker 1: other questions to ask, like what is the carbon footprint

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Speaker 1: of actually building the solar tower, but I would argue

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Speaker 1: that whatever it is, it probably has significantly less than

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Speaker 1: the carbon footprint produced over the lifetime of a coal

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Speaker 1: plant or a gas plant or oil plant. Um I

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Speaker 1: think that's pretty a pretty fair assumption, but it still

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Speaker 1: could be a very large upfront uh carbon footprint creation there.

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Speaker 1: So that's kind of the approach that I wanted to

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Speaker 1: talk about, this idea of being able to generate electricity

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Speaker 1: twenty four hours a day using sun power without being

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Speaker 1: a solar panel, and I thought it was a really

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Speaker 1: cool approach to that, something that could really get around

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Speaker 1: a tricky problem with solar power because I know a

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Speaker 1: lot of critics point out, hey, if the sun is

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Speaker 1: not shining, then you're not making electricity. Well that's true

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Speaker 1: with your traditional solar panels, but not with solar towers,

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Speaker 1: assuming that you don't enter into some cataclysmic event where

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Speaker 1: you've got crazy overcast skies for a really long time,

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Speaker 1: in which case, if we do have that, we're gonna

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Speaker 1: have other problems besides where we get our electricity. Um Oh,

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Speaker 1: and you might want to know how much electricity can

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Speaker 1: one of these facilities generate. It would be good for

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Speaker 1: me to tell you that. So Solar Reserves says that

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Speaker 1: depending on the plant design, it can generate between fifty

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Speaker 1: and two hundred megawatts on electricity, and one megawatt is

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Speaker 1: enough power to supply around a thousand homes. So you're

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Speaker 1: talking about with one solar tower facility between fifty thousand

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Speaker 1: and two hundred tho and homes. Obviously, there are a

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Speaker 1: lot of cities that are bigger than that, and in

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Speaker 1: order to supply the electricity for those cities, you would

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Speaker 1: need multiple solar tower facilities to to do that. Uh.

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Speaker 1: And again that's another question is where would this be

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Speaker 1: most appropriate. Obviously a lot of desert towns that have

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Speaker 1: medium to small populations, this would be an amazing approach

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Speaker 1: to generating electricity, but it might not work for someplace

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Speaker 1: like New York City for multiple reasons, the population size,

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Speaker 1: the lack of land to dedicate to solar power. Obviously,

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Speaker 1: that's another issue is that if you are going to

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Speaker 1: dedicate a land to a solar tower facility, you're not

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Speaker 1: able to use that land for other stuff, at least

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Speaker 1: not easily, So that's another consideration. Obviously, you don't want

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Speaker 1: to end up going to a place where you're dedicating

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Speaker 1: land that could be otherwise used for a more productive purpose,

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Speaker 1: possibly not energy related. It might be food related, or

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Speaker 1: water or something along those lines. So a lot of

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Speaker 1: things to take into consideration. But I think it's a

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Speaker 1: very elegant approach to generating electricity in a using a

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Speaker 1: renewable resource the Sun's energy, and very low impact to

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Speaker 1: the environment. The modern salts are inert they're not dangerous. Uh.

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Speaker 1: They're obviously dangerous in their temperature. You would not want

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Speaker 1: to touch them while they're at a thousand fifty degrees fahrenheit,

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Speaker 1: but they're not dangerous to the environment. Uh. And these again,

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Speaker 1: the systems are separate. The water system and the salt

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Speaker 1: system are separate from each other. So I think it's

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Speaker 1: a really interesting approach. Now I'm curious to hear what

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Speaker 1: you guys think about the most promising energy sources for

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Speaker 1: the future. Do you really think that solar power is

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Speaker 1: going to become a major way to offset our electricity generation.

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Speaker 1: I'm pretty sure. I feel fairly confident it's never going

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Speaker 1: to be the primary way we generate electricity. I don't

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Speaker 1: think gets practical enough to be our primary but I

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Speaker 1: certainly see it as a very strong contender for a

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Speaker 1: support system, something that can offset some of our electricity needs.

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Speaker 1: But what do you think? Do you think there are

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Speaker 1: other ones that are better? Do you think wind power

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Speaker 1: is better than solar? Or maybe uh, maybe you think

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Speaker 1: hydro power is better. Maybe you think geothermal. Maybe you're

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Speaker 1: looking for that nuclear fusion approach. If that break, If

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Speaker 1: there is a breakthrough nuclear fusion, that would be an

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Speaker 1: enormous benefit to all of humanity because we would suddenly

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Speaker 1: be capable of going into an era of energy surplus,

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Speaker 1: which would be phenomenal. And I hope it happens, but

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Speaker 1: there are a lot of challenges to get out of

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Speaker 1: the way first. So maybe I'll do a full episode

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Speaker 1: about nuclear fusion in the in the future and talk

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Speaker 1: about why it's such a tricky issue. Guys, I hope

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Speaker 1: you enjoyed that classic episode of tech Stuff. I'll be

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Speaker 1: back soon recording on episodes. I can't wait to hear

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Speaker 1: from you. If you have anything you want to send

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Speaker 1: to me, maybe it's a suggestion for a future episode,

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Speaker 1: send me that via email. The addresses tech Stuff at

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Speaker 1: how stuff works dot com, drop on by our website

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Speaker 1: that's tech stuff podcast dot com, and I'll talk to

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Speaker 1: you again really soon. For more on this and thousands

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Speaker 1: of other topics, because it how stuff works. Dot com