Intro
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Have you ever heard of the Archimedes' Death Ray? It's an
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ancient Greek myth that dates back to 212 BC and tells a story
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of how Archimedes used bronze shields to concentrate the sun's
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rays to set fire to invading Roman ships. This ancient idea
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has evolved into modern day concentrated solar power, CSP,
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where instead of using shields to concentrate the sun’s light,
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we use mirrors. And instead of setting ships on fire, we use
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the heat to drive a steam generator. But does CSP make
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sense in the modern era, or should it stay ancient history?
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In this video, I'm going talk about how CSP works and the
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different technology options. We’re going to look at how it is
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different from solar photovoltaics, with or without
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batteries, plus I'll explain why I think CSP's time to shine
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might have arrived. I’m Rosie Barnes, welcome to Engineering
History of Concentrated Solar Power
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with Rosie. Concentrated Solar Power, or CSP, is surely the
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coolest-looking renewable energy technology. So cool, in fact
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that it was used by the villain in a Bond film, The Man with the
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Golden Gun in 1974. So here I am telling you that the cool
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futuristic technology that's going to help solve our energy
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crisis is the same cool futuristic technology that was
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going to solve the oil crisis back in the 1970s. Okay, so it
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looks futuristic, but it's not new now. And it wasn't even new
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when that Bond villain was blowing stuff up with his solar
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laser 50 years ago. That story that I mentioned at the start,
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that Archimedes was concentrating the sun to set
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Roman ships on fire more than 2000 years ago. Well, most
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people assume that story was a myth. But in 1973, a Greek
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scientist demonstrated how mirrors can be used to reflect
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and concentrate light onto an object at a distance of 60
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meters away, causing it to catch by within minutes. His
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experiment showed us that this ancient tale may not have been
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just a legend after all. In more modern time, CSP's first
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documented use was in 1866, when Augustin Mouchout used parabolic
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troughs to heat water and produce steam to run the first
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solar steam engine. And then in Egypt in 1912, CSP was used to
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power steam pumps to irrigate vast areas of the desert. The
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first operational concentrated solar power plant was a one
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megawatt system built in Italy in 1968. Then the oil crisis
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happened and caused a flurry of activity to develop alternative
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energy technologies, including CSP. As a result of this by
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1982, there was a 10 megawatt demonstration project in the
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United States, which was incrementally developed up to
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about 350 megawatts by the late 80s. The oil crisis had ended by
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that time, so it was a bit of a dead end for a while in the US,
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at least. In the early 2000s, there was a lot of CSP action in
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Spain, and by 2010, there were 34 CSP plants worldwide,
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totaling 880 megawatts. Fast forward to today there is over
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five gigawatts worldwide spread mostly between Spain and the US,
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but with China and other countries starting to catch up.
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So there is a lot of growth in fits and spurts but nothing like
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the rollout of other renewable energy technologies, solar PV
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and wind, which also started small in the 80s and 90s. But
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now each nearly 200 times the installed capacity of CSP. So
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since CSP has been around so long, Surely it would already be
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a mainstream energy source if it was ever going to be? or maybe
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not. I think until now, CSP has been a technology ahead of its
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time, but that might be about to change. To explain why I think
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that let's start with how it works and the different
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technology options available. Concentrated solar power works
The Different Types of CSP Systems
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by concentrating and capturing the thermal energy from the sun
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into a focal point. It's pretty similar to a kid using a
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magnifying glass to concentrate sunlight to burn a hole in a
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piece of paper. This concentrated heat can be used to
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heat a fluid such as molten salt which can be stored for hours or
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days. The heat is used to create steam to power a steam
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generator, which is the same kind of generator used in a
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traditional thermal power plant like coal, conventional gas or
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nuclear. There are three main ways that you can concentrate
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the sun's heat using either a tower, a couple of variations of
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a trough design or a dish. The tower design, also known as a
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power tower or central receiver, has a receiver on top of a tower
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that's surrounded by hundreds of heliostats, which are small
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individual Sun-tracking mirrors that reflect the sunlight onto a
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single point at the top of the tower. This concentrated light
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heats up the receiver which contains a heat absorbing
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material such as molten salt. The heated molten salt then
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travels to storage tanks below the receiver. Instead of
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concentrating at a single point on a tower. You can also
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concentrate in a line using the trough method, also known as a
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linear receiver. The trough mechanism is curved in a
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parabolic shape and tracks east to west following the sun. It
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focuses the sunlight to a line which contains heat transfer
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fluid blowing down that linear receiver. There's also a
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variation, the Fresnel aka linear trough, which instead of
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a mirrored trough uses mirrors and facets that move
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individually and focus everything onto a long thin
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receiver. In this case, the receiver doesn't need to move
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since the mirrors move instead, the advantage is that the whole
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thing is on the ground, so you need less supporting structure.
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And because the receiver doesn't need to move, it's easier to
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deal with the heating fluid and you could potentially directly
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heat molten salt instead of the thermal oil that's typically
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used in the trough designs. And finally there are dishes. They
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use parabolic mirrors to focus sunlight onto our receiver, the
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mirrors and receiver can move in two axes, so the entire area is
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always facing straight at the Sun. This makes them more
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efficient than the other options. With a tower, in the
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morning in the afternoon, the sun's glancing off it at a quite
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a low angle and so the projected area of the mirror to the sun is
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quite small relative to its area, and the troughs track east
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or west but when the sun's low in the sky in winter, the whole
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trough is seeing an oblique angle so it's energy capture is
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compromised too. The dish is the most efficient method and it
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was popular early on, but they've pretty much vanished
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commercially, mostly because it's more complex than the other
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methods. Because the receiver moves with the dish to follow
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the sun, the pipe that transports your hot fluid has to
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move too, so you've got to move liquid hot stuff through axes of
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rotation, or you can avoid that by generating electricity at the
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receiver, but then you lose the major advantage of CSP, which is
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its storage capability. So those are the main technology
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options for CSP. And like in so many other technologies that I
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cover on this channel, there's a trade off here between
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efficiency and complexity. Most of the installed CSP plants use
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a trough design, but the companies that are most
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aggressively expanding these days are tending more towards
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the tower design. If you're interested in learning more
Thanks to Brilliant for sponsoring this video!
6:12
about the special parabolic mirrors used to reflect the
6:15
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6:19
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6:40
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6:52
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CSP vs PV
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Because CSP generates electricity from the sun, it's
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tempting to consider it as a direct alternative to solar
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photovoltaics (PV) and in the early days for both technologies
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around the 90s. That was pretty much how it was treated.
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Northern Europe with more cloudy weather unsuitable for CSP did
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photovoltaics and Spain with clearer skies did CSP without
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any storage at first. Until about 2010, PV and CSP were
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fighting it out on cost per kilowatt hour, then the cost of
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energy from PV dropped much faster. This was due to its
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steep cost reduction curve helped by the fact that it was
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largely northern European countries pushing hard on
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renewables rollout in the 2000s and 2010s. And that kind of
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brings us to today where energy from PV costs less than half
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what it does from CSP. I don't think anyone expects this trend
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to reverse. So CSP has simply lost the battle to be the
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dominant solar power technology. But that isn't the right battle
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for CSP to even be in. PV provides very cheap power when
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the sun is shining. But only when the sun is shining. In the
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early days of the energy transition when there wasn't
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much solar power in the grid. That was all that was needed.
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The grid could soak up whatever amount of solar whenever it was
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generated, and everyone just wanted as many renewable
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kilowatt hours as possible for as cheap a price as possible. PV
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did that amazingly well. So well, that by now some grids
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like Australia's is starting to have significant solar
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penetration enough to be really affecting the way the
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electricity grid operates and negative prices and curtailment
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of renewables during very sunny days have become really common.
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CSP won't cause problems like this, because in addition to
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generating power, it can store it And this fact provides three
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benefits when used in today's grid. One, you can provide power
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after the sun sets and two, you can take advantage of higher
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electricity prices so the value is greater. Meaning it's not as
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relevant that the cost from energy from CSP is higher than
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from PV. So that's great and all but obviously, CSP isn't the
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only form of storage for renewable energy. Battery
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storage has come a long way since the early days of solar
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versus CSP. And surely we can simply add a lithium ion battery
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to a PV system to get the best of both worlds: cheap energy
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generation from PV and cheap energy storage from batteries.
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Does CSP lose again? maybe not. And that's because of benefit
What about CSP vs PV + Battery?
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number three, that the cost of energy from CSP actually gets
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cheaper as storage duration increases, which is the opposite
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of what happens with a PV plus battery system. There's a few
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reasons why first, having storage means that you don't
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need to use the energy right when it's generated. So in the
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middle of a sunny day, when the grid is totally saturated with
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solar power, and some of it is being curtailed, you're able to
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store your energy for later and so, avoid curtailment. Second,
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because CSP includes an expensive steam turbine, adding
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storage capacity means that you can run that turbine much closer
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to full capacity, 24/7 If you want to size it that way. CSP is
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an expensive way to convert sunlight to electricity, but
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it's very cheap storage. In contrast, PV panels plus a
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battery, are very cheap conversion of sunlight to
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electricity, but expensive storage. So if you only want one
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hour storage, it's great. But as you increase the storage
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duration to six or 12 hours say, then the battery gets more and
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more expensive. And CSP then becomes a cheaper option. At
CSP as Long Duration Storage
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long durations, its cost is on par with pumped hydro, which is
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my other favorite long duration energy storage, especially when
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it's off river pumped hydro, which you can check out in this
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video. Above all, CSP is a generator with storage so you
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can rely on it. It shouldn't be competing against solar PV, it
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should be competing against traditional coal and gas
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turbines. And that's why I think CSP's time to shine is coming up
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soon. Coal is exiting the grid around the world, whether
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because of government action, or as cheaper renewables destroy
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their business case. The latter is what's happening here in
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Australia, where 1/3 of coal power plants have already
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announced they'll close by 2030. And more announcements are
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expected to take that up to about two thirds closed by the
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end of this decade. Coal contributed nearly 60% of
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Australia's electricity last year and two thirds of that is
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not going to be available in less than a decade. To replace
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it, we will need hours of storage, longer than what
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lithium ion batteries can provide cheaply. But can CSP
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really supply electricity that we will be able to rely on? It's
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still based on solar power after all, and even though we can be
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reasonably sure that the sun will rise every single day,
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sometimes it's cloudy, and CSP needs fairly clear skies to work
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well, plus the energy is stored as hate and we all know that hot
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things cool down so that energy will be gradually lost if we try
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to store it for days, weeks or months at a time. Actually,
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neither of these issues are as big a deal as you might think.
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If the CSP is located appropriately, there are lots of
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desert locations where skies are clear nearly all of the time.
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And when they're not that's forecastable. What will be
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needed in a fully renewable electricity grid will be firm
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dispatchable capacity, meaning it's always available when you
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need it, it doesn't mean 24/7 constant electricity generation
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because demand isn't constant 24/7. And also because solar and
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wind power provide much cheaper energy when it's available. So
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we'll use those when we can and we mainly just want to fill in
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the gaps when it's not very windy or sunny. But you do need
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power to be always available. Gas turbines traditionally fill
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that role, they mostly sit idle and then every evening or
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whenever price goes up, you fire them up, but they're far from
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24/7 constant generation, and crucially, the times they're
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needed are mostly known quite far in advance. So if in the
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future, we've replaced most of our gas generation with CSP, if
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the weather forecast says there are sunny or windy days coming
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up the CSP plant might generate all night every night and a bit
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in the morning. But if we see a shortfall coming up in a few
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days, and also see that cloudy skies above the CSP plant are
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forecasted on those same days, well, we'll just make sure it
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remains charged up. So you'd reserve your output for just the
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early evenings when it's most needed. The thermal storage only
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loses about 1% of its energy per day. So you can easily ride
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through several cloudy days like that. And in the locations where
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these systems are going, that's the longest that you'll need to.
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If you put 15 hours plus storage on a CSP plant, it can actually
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have very close to the same firming value as a gas turbine,
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it's almost always going to be there when you need it. And I
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know that people in the comments are gonna latch on to that word,
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"almost"... almost always available isn't good enough for
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the grid overall. But the last tiny little bit of reliability,
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and we're talking fractions of 1% here, the last little bit
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will be filled with something more expensive, like hydrogen,
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or even fossil gas would be fine, since it's practically
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never used, and therefore creates practically no
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emissions. And remember that all of our generators are only at
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best, "almost" always available, coal, gas, nuclear, whatever,
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they all have unexpected shutdowns that need to be
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planned for. Like I mentioned before pumped hydro systems with
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15 hour storage can do much the same thing at the same cost of
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CSP. So we could end up with pumped hydro in the mountains
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and CSP in the deserts to keep the lights on once all the coal
The Scale of CSP Systems
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has closed. To replace coal power plants, we're going to
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need large scale solutions, our CSP plant needs to be quite big
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to be cost effective, largely because it uses steam turbines,
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and they're much more efficient when they're bigger. I mean, no
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one makes a one megawatt coal fired power plant anymore. And
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for the same reasons you wouldn't make a one megawatt CSP
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plant, you're looking at 50 megawatts and upwards. So that
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sounds big, and it is big compared to a single PV panel.
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But if you think about the size of a coal power plant,
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Australia's largest, Eraring power station, which is going to
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retire in 2025, is 2.8 gigawatts. So to replace that,
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with CSP, even if you're building 100 megawatt units say,
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you'll still need to build 28 of them. So can it be done? Given
So why isn’t CSP more popular?
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that CSP has been around for ages and yet seems remained a
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kind of fringe technology, you might assume that previous
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experiences have been bad. Otherwise, wouldn't we see a
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whole lot more CSP plants around the world. In fact, some of the
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plants in California that were built in the 80s are still
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running after 40 years so it's not that. It's just that until
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coal power plants actually start closing in large numbers. We
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don't yet need the type of generation and storage that CSP
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provides. But coal plants are closing soon and CSP or whatever
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long duration storage technology you prefer. These don't just
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spring up overnight. The day a coal power plant closes, it
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takes around three years to build a CSP plant. So a little
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forward planning would be beneficial if we want a smooth
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transition away from coal. There are movements in the right
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direction, country Just like China, Morocco and others have
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started installing a lot of CSP. And here in Australia, we're
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finally starting to talk about a mechanism to incentivize long
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duration storage in a similar way to how renewable energy
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certificates have been incentivizing renewable
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generation for years now. So expect big things from CSP in
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the next few years. And I'll be following closely to see how it
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plays out. I got a lot of generous help from Dr. Keith
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Lovegrove for this video. Keith taught me thermodynamics at uni
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about 20 years ago and has been working on CSP for even longer
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than that. He's agreed to be a guest expert on a live stream on
15:33
CSP technology that's coming up in about a week. So if you've
15:36
got questions or ideas, please write them in the comments or
15:40
even better join us live. As always big thanks to the
Outro
15:43
Engineering with Rosie Patreon team, whose support is a reason
15:46
why I'm able to get paid help researching and editing these
15:48
videos. If you'd like to join the team, there's a link in the
15:51
description. Thanks for watching and I'll see you in the next
15:54
video.
