
In Pictures: The World’s Largest Solar Thermal Power Plant - olalonde
http://www.technologyreview.com/energy/40460/?p1=A1
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anusinha
Basic thermodynamics: converting heat into work is inefficient. A photovoltaic
can go straight from the energy of the photons (admittedly restricted to a
particular band that they were designed for) with less loss.

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leoedin
That's a slightly glossed over interpretation of thermodynamics. Perhaps
photovoltaics have a higher theoretical efficiency than a thermal cycle plant,
but in practice they don't. Thermal cycle power plants are the mainstay of our
power generation - nuclear, coal, gas, geothermal - all those power sources
make use of a steam based heat to work cycle. We've got 100 years of
experience in developing thermal cycle power. Peak photovoltaic efficiency is
currently ~20%, while most affordable cells are closer to 10-15%. A simple
cycle thermal plant might have an efficiency of 30-40%. It'll be some time
before photovoltaics are more efficient for a given area of collecting space.

Cost is a different question. Photovoltaics have fallen dramatically in cost
recently. As the space taken up by a solar plant isn't really an issue (the
collecting area could take up 10 times more space without really impacting
anything), the winner in solar energy will be the cheapest option per kWh.

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sinsear
I can't help myself to think of "Fallout: New Vegas".. you know, a massive
solar-power plant near Last Vegas with mirrors "aiming" for a huge tower.. :D.
Other than that, really interesting read :)

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redwood
Very cool stuff. I have to say I'm very impressed to see a project like this
actually getting off the ground. After working for a few years in California's
energy regulatory sphere you can become very cynical about the ability to
build much of anything, especially when environmental impact statement
proceedings can be used by NIMBY (or any other) concerns to stonewall just
about any project for just about any reason, if they've got money.

Looks like Brightsource found the right location where there aren't too many
folks worried about the development, and whether or not solar thermal will
indeed become a growth industry they've at least set a precedent for this kind
of work (and regulatory process) in the 21st century, which is an important
development.

I hope Brightsource's decision not to go public was only a good rational
choice rather than a sign of a company going under.

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glabifrons
Most impressive... I wonder how it looks from the air.

It's 74 times as powerful as this one I spotted while flying into Albuquerque
several years back.
[http://maps.google.com/?ll=34.962827,-106.509635&spn=0.0...](http://maps.google.com/?ll=34.962827,-106.509635&spn=0.00386,0.003911&t=h&z=18)
I'm pretty sure that is this one: <http://energy.sandia.gov/?page_id=1267>

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thrownaway2424
I love the juxtaposition of this facility with the absurd desert golf resort.
A good contrast of America's disastrous 20th century with a glimmer of hope
for the future.

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mparlane
Does anyone know the long (really long?) term effects of turning sun energy in
to electrical? I refuse to beleive it has a zero impact. We take heat energy
away from the ground, so the ground gets cooler right ? And over a long period
the ground is no longer heated the same as it use to, so that cools the top
crust, which would cool the crust below etc. Thoughts? (I am nowhere near
qualified to ask these questions)

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underwater
The amount of energy extracted is minuscule. Digging coal an uranium out of
the ground aren't side effect free either.

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borism
Indeed. The geological effects of mining are much more serious than solar
energy, which are not zero still (you need mining to produce solar
panels/mirrors).

Most side effects are focused on local biosphere I'd guess.

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trothamel
I wish that, when quoting the maximum output of a power plant, news articles
would also quote the capacity factor - basically, the percent of the maximum
output that a plant achieves long-term.

This plant is likely to have around a 40% capacity factor, which is much
better than the 20% or so photovoltaic solar achieves, but it's much lower
than the 85-90% that baseload plants achieve.

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mchannon
Capacity factor is location- and weather-dependent, and not always known for
certain with a new technology (or in this case a known technology this much
larger).

Concentrated solar thermal also allows for storage, making the capacity factor
percentage adjustable, and allowing for on-peak optimization, which would have
a lower capacity factor but a significantly higher benefit to the power
company.

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makmanalp
Does anyone know how they handle the problem of the mirrors tarnishing and
getting dirty over time?

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edj
Don't know about tarnishing, but for cleaning they most likely use water.

From an article on solar thermal plants in the Middle East [1]:

 _But harsh desert conditions in parts of the MENA region generate large
amounts of airborne dust which collects on the solar panels used in CSP
systems, reducing their efficiency. They need regular cleaning, which consumes
large amounts of water._

1: [http://m.scidev.net/en/climate-change-and-
energy/renewable-e...](http://m.scidev.net/en/climate-change-and-
energy/renewable-energy/news/abu-dhabi-bets-on-anti-dust-solar-panels.html)

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robertp
I went past the construction site on my way to vegas last week. It looks like
all 3 towers are at the full height.

It looks really crazy from the highway with the large towers and circles
below.

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yumraj
Personally, I think this is the most ridiculous concept. I have not seen the
math but in order to achieve any meaningful scale it needs to be huge, but on
the flip side the farther you get from the center the efficiency reduces
drastically.

Moreover, this is a dusty desert, what are their plans for cleaning those
mirrors, at such a huge scale. The only guy who will make money in this is the
one with that contract.

The inventor had tried this earlier, I believe in Israel, but that had failed.

Oh well, with federal loan guarantees that it has, we have another Solyndra on
our hands.

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redwood
You an see an early version of one of these in Barstow, if that's what you're
thinking of. There is a functional one in Spain as well
(<http://en.wikipedia.org/wiki/PS10_solar_power_tower>)

Anyway you may be right that the tower concept isn't going to last long, but
the troughs have been shown to last decades (see Victorville, California) and
obviously they have the same issue of dust... so there must be a known
solution for that engineering challenge.

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thangalin
Possibly hydro- and oleophobic mirrors plus elbow grease.

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truebosko
Clean energy in a vast open space that will be ripe for greenery and natural
wildlife as soon as the construction crews are out of there.

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buo
What I'd like to know is, what is the temperature at the tower, where all
beams converge?

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mchannon
They probably keep it at under 1000 degrees by circulating a molten salt at
whatever rate is necessary to carry away the heat.

No matter what the target is made out of, without that circulation to withdraw
heat, it wouldn't get much hotter before it vaporized and there was no target.
No doubt it'd be possible to get a much higher temperature if that was the
goal.

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glabifrons
Maybe, if you mean Celsius. Salt melts at 1474F (801C), so it'd have to be
kept above that or it'd crystallize.

I've always wondered what they do if the conditions don't provide a high
enough temperature... seems they'd have to drain it entirely of it's salt
before it solidifies, or they'd never be able to get it restarted. That is,
unless they have some form of heater all the way through the plumbing to melt
the salt so it'll flow.

I first read about using salt this way back in (Popular Science? in) the
early/mid-'80s with a parabolic reflector heating the salt to be pumped to a
Stirling engine. They didn't address that question then either.

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mchannon
I referred to "a molten salt", which in practice is never sodium chloride;
probably because its melting point is higher than some superior alternatives.

Molten salt is used for two reasons.

It is the best real-world conductor of heat you will find. If you heat a
miles-long pipe of molten salt on one end, that heat will make its way to a
temperature rise on the other end in surprisingly rapid fashion. But this is
only true when it is molten. Naturally, if molten salt encounters its solid
salt, the solid melts pretty easily to expand the volume of molten salt.

Molten salt stores quite a bit of energy in its phase change, and of course as
a salt solidifies, it becomes more dense. This means the top salt (at the
collector) will always be the slowest to solidify.

Not sure where all this worry about "freezing to death" comes from. The salt's
effectiveness comes from its conduction, not its flow.

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ivarious
Makes me wonder if crop circles were the remnants of some sort of solar
energy-tapping constructions.

