
Crescent Dunes, a utility-scale solar power plant in the Nevada desert - prostoalex
http://time.com/4291347/crescent-dunes-solar-power-plant/?xid=time_socialflow_twitter
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rgbrenner
"All night" isn't quite true. It has 10 hours of storage. And if you want full
capacity, you have to start tapping into that in the evening.

Also what's cool about this plant, is that it doesn't use natural gas in the
morning to heat up the molten salt (like other plants). The salt never cools
completely during the lifetime of the plant.

Expensive though.. on a 25 year contract at 13.5 cents per kwh. That'll be
renegotiated after the 25 years at a much lower rate. Utilities pay higher
prices for new plants (gas, oil, etc) to pay off the cost of building it.
After that, it drops to a more reasonable price.

[https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr...](https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project)

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honkhonkpants
Doesn't "hours of storage" necessarily imply a rate of discharge? If you don't
take any steam off it, doesn't it last more than 10 hours? It seems like they
should just state the storage in terms of extractable energy stored.

And why sodium? It does not have a spectacular specific heat. Is it just
convenient due to its high boiling point?

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rgbrenner
Yes.. they do state the storage in terms of energy. When plants state hours,
it's at full capacity. So 110MW capacity x 10 = 1.1 GWH of storage. Of course
it will operate longer if you use less than full capacity.

Molten salt is used because it's liquid at atmospheric pressure, is low-cost,
its operating temperatures are compatible with the most efficient steam
turbines, and it is non-flammable and nontoxic.

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ChuckMcM
Its great these things are coming online, they have issues when the mirrors
get out of alignment. From lighting the lower parts of the tower on fire [1]
to blinding pilots flying nearby [2].

[1] [http://www.latimes.com/local/lanow/la-me-ln-solar-plant-
fire...](http://www.latimes.com/local/lanow/la-me-ln-solar-plant-
fire-20160520-snap-story.html)

[2] [http://www.geek.com/news/worlds-largest-solar-power-plant-
is...](http://www.geek.com/news/worlds-largest-solar-power-plant-is-forcing-
pilots-to-fly-blind-1588349/)

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tomp
This is really two things in one - a solar plant, and an energy storage
system. Couldn't we decouple them? I.e. when electricity is cheap (Germany
during the day can dip to zero), heat up the salt, and discharge it at night
(actually, in the evening, when electricity is most expensive).

Also, I wonder how it compares to big batteries?

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jws
This is not a photoelectric plant. It is a sunlight concentrator to heat salt
which stores energy which is eventually used to drive a steam turbine and turn
a generator. All one thing.

You could use molten salt to store electricity on its own, but I think the
efficiency would make it undesirable. A steam turbine is something like 50%
efficient and is probably the least efficient part of the system, so it just
gets worse from there. For comparison, lead acid batteries are above 70%
efficient.

~~~
ams6110
But if electricity is free during the day (I guess because of oversupply from
wind and/or solar?) who cares about a 50% loss?

I wonder if using the heat directly e.g. with a Stirling engine/generator
would be any more efficient?

Lead acid batteries are an environmental nightmare compared to molten salt.

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Tharkun
Electricity wouldn't be free during the day if you wasted 50% of it.

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markokrajnc
In Spain already since May 2011:
[https://en.wikipedia.org/wiki/Gemasolar_Thermosolar_Plant](https://en.wikipedia.org/wiki/Gemasolar_Thermosolar_Plant)

~~~
neolefty
No doubt they learned a lot from Gemasolar. The article describes Crescent
Dunes as the first "utility scale" plant. The wikipedia page is a bit more
quantitative, listing its capacity at 125 MW, vs Gemasolar's 20MW:

[https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr...](https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project)

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bane
I've started to become more and more convinced that the longer term view of
the power grid is that it may no longer supply an assumed base-load. Instead
every electronic device will end up having some measure of chargeable battery
backup along with the building/facility the device is in. Over a day the
batteries will soak up power and charge and at night they'll power the
devices.

Current thinking about power grids is that power generation is cheaper at
night because people are using it less. But in a solar powered system, power
generation during the day is essentially free, it's the capture devices (and
storage devices) that cost anything.

This notion helps the power companies share and distribute the storage costs
while making the direct users of the power responsible for sizing their
storage costs.

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MawNicker
I'm sure they researched this but square panels seem suboptimal. I wonder if
manufacturing made that determination. It seems like circular or hexagonal
panels would better utilize the space. That or just grid aligned square
panels. Maybe the space efficiency doesn't matter that much? Each
configuration captures the entirety of indirect sunlight. The little bit extra
you'd get from direct sunlight is likely insignificant compared to overall
performance.

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pdonis
I don't think the panels are the limiting factor. Remember this isn't a
photoelectric plant; the sunlight isn't being converted directly into
electricity. All the panels are doing is reflecting sunlight to the central
tower, where it heats up molten salt. The limiting factor for power generation
is probably the heat capacity of the salt, not the amount of sunlight the
panels can reflect.

Also, the panels don't look like flat squares to me; they look curved, so that
they concentrate the sunlight they reflect.

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jdeibele
[http://www.wired.com/2016/05/huge-solar-plant-caught-fire-
th...](http://www.wired.com/2016/05/huge-solar-plant-caught-fire-thats-least-
problems/) has a decent summary of the problems with this type of solar.

I was surprised that the Ivanpah fire wasn't mentioned in the Time article but
then it seemed pretty rah-rah.

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RangerScience
I drove by this plant to/from Further Future. The concentration of light
around the central towers was so intense, it was visible - a light, glowing
cloud (clearly in the "shape" of the reflected light) surrounding the central
tower.

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london888
If transmitting power was more efficient we could just have solar in the lit
time zones powering those in the dark.

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neolefty
Exactly. With our current techniques -- high-voltage or superconducting lines
-- as I understand it, it's more expensive to transmit than to generate
"locally" (within a few hundred miles?). I'd be curious to see the tradeoff
(1) researched better and (2) visualized quantitatively.

~~~
niftich
Sorry I don't have exact numbers for you, but there do exist some very long
HVDC lines [1]. The longest as of writing is in Brazil at 2385 km. There is a
fairly long one in the US at 1360 km between the Columbia River Gorge and the
Los Angeles basin [2].

But given that the solar terminator moves at about cos(latitude) * 1668 km / h
(so slower towards the poles), even at a generous mid-Europe latitude of 45° N
it'd be moving at 1180 km / h, giving you only a 2-hour window to make use of
such a scheme with the HDVC lengths we have now. But hours before sunset,
you're probably not at peak solar production anyway.

[1] [http://www.power-technology.com/features/featurethe-
worlds-l...](http://www.power-technology.com/features/featurethe-worlds-
longest-power-transmission-lines-4167964/)

[2] [http://new.abb.com/systems/hvdc/references/pacific-
intertie](http://new.abb.com/systems/hvdc/references/pacific-intertie)

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london888
I think there's one being built in Israel too?

