
24-Hour Solar Energy: Molten Salt Makes It Possible - pmoriarty
https://insideclimatenews.org/news/16012018/csp-concentrated-solar-molten-salt-storage-24-hour-renewable-energy-crescent-dunes-nevada
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acidburnNSA
Peripherally related: molten salt thermal energy storage is also something the
nuclear industry has been considering using to help improve load-following
economics of nuclear in a heavily variable renewable world. The idea is the
nuke would run 24/7 at constant power but the load of the plant would be
swapped from the thermal storage tank (in the day while solar is providing all
the electricity) to the grid. Meanwhile, the load of the solar thermal system
would be turned off during the day and turn on at night. This effectively
doubles the power capacity of the nuclear plant to help fill in the duck curve
as the sun sets.

Doesn't help with seasonal renewable variability, but for day-to-day, it's
pretty slick. The cool thing over TFA is that now it can work in many more
geographic areas (e.g. where solar thermal doesn't make as much sense due to
low intensity sunlight and there's more solar PV).

Conventional nukes aren't great at going to these temperatures so this is
mostly a thing "advanced" reactor people talk about.

e.g.:
[https://inldigitallibrary.inl.gov/sites/sti/sti/6339782.pdf](https://inldigitallibrary.inl.gov/sites/sti/sti/6339782.pdf)

Of course then there are molten salt cooled/fueled reactors, which is
different from energy storage, making this topic even more confusing.

~~~
ambicapter
> Conventional nukes aren't great at going to these temperatures so this is
> mostly a thing "advanced" reactor people talk about.

Are the temperatures too high or too low?

~~~
Analemma_
Too low - water-cooled reactors are designed to bring the water in the
secondary cooling system to _just_ above the boiling point, because anything
beyond that is wasted energy (the temperature of the steam doesn't really
matter as far as driving turbines). So retrofitting a molten-salt system onto
these reactors isn't very efficient and you would ideally want a new reactor
design intended for that from the beginning.

~~~
SECProto
> (the temperature of the steam doesn't really matter as far as driving
> turbines)

This goes against everything I seem to remember from thermodynamics -
superheated steam is exactly what is used for driving turbines, with saturated
steam as the cold side outlet of the turbine. It's what makes district heating
useful - there is still heat energy left in the saturated steam, too low grade
for driving turbines, but still useful for heating apartments etc

~~~
mcguire
What's your turbine pressure? Steam at 700°F is apparently 3000psi, which is
the highest temperature/pressure I can find.

Edit: Best Q/A thread I've seen recently:
[https://www.researchgate.net/post/At_what_temperature_water_...](https://www.researchgate.net/post/At_what_temperature_water_will_decompose_to_Oxygen_and_Hydrogen)

" _We need this value to be more specific numerical form to utilize in design
of high temperature and high pressure steam boilers and turbines working at
300 bars._ "

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anon1253
These types of systems are generally not competitive with PV for electricity,
since they require a lot of concentrated solar energy thus limiting the
options for deployment. However, they are great for generating heat. And with
heat you can trivially desalinate water. Since trees can be a nice carbon
sink, I've often wondered if this type of scheme might make sense:

\- Plant heliostat molten salt reactors in desert coastal areas (the
concentrated solar kind)

\- Use generated heat to desalinate water (e.g. Multi-stage flash
distillation)

\- Use desalinated water to provide irrigation

\- Plant (potentially GMO'ed) trees and other bootstrapping organisms to
"green" the desert

\- Rinse repeat.

The net effect is that you can potentially turn large swaths of desert into
forests, with minimal external energy requirements (and potentially build an
agricultural community around them, more or less self contained in terms of
water/energy)

~~~
XaspR8d
Tangent - is there a systems reason (aside from the "base ecological ethics"
of wanting to preserve biodiversity and not eradicate any unique ecosystems)
why humans would _not_ want to get rid of deserts?

Obviously having more arable or at least livable land is useful to human
society, but I generally assume that messing with _any_ large scale climates
or biomes has adverse effects. I'm not yet aware of what that would be for
deserts though. I suppose they have fairly high albedo, unlike most land
formations that can exist in lower latitudes.

(To be clear my own views aren't necessarily so utilitarian and I like
deserts. Just curious about a rational geoengineering civilization might do.)

~~~
jerf
Some deserts are quite natural. It doesn't matter what you do to them short of
knocking down the mountains upwind of them, they're going to be deserts.

Some are not.

I consult my mental image of deserts and I observe that the Sahara is almost
devoid of life, whereas the deserts of the American Southwest are rich and
diverse despite their lack of substantial rainfall. (The latter I've also
visited and spent some time in. I've never been to the Sahara to know if
that's correct.) If my mental image is accurate, fixing the unnatural, almost
entirely uninhabited desert would be nothing but a win. "Fixing" the natural
kind would be relatively destructive of an existing ecosystem.

(Then you get into the question of "how do you valuate and compare two
different ecosystems?". I've thrown that gauntlet a couple of times and I
don't think I've even seen anyone _engage_ with that question properly in a
non-knee-jerk way. The heuristics people have been taught to use about
environmentalism do not admit of that question even existing.)

~~~
toss1
Also note that some deserts are variable, and human activity can tip the
balance [1].

especially considering the global carbon balance, it seems that tipping some
parts of the desert back to forest would be a net plus. Humans are already
doing massive uncontrolled experiments with bad results, it may help some to
do some deliberate experiments with good foundations with the goal of creating
good results?

[1] [https://www.smithsonianmag.com/science-nature/what-really-
tu...](https://www.smithsonianmag.com/science-nature/what-really-turned-
sahara-desert-green-oasis-wasteland-180962668/)

------
fphhotchips
Sadly, the South Australian plant fell over financially:
[https://premier.sa.gov.au/news/statement-regarding-
solarrese...](https://premier.sa.gov.au/news/statement-regarding-solarreserve)

[https://www.abc.net.au/news/2019-04-05/solar-thermal-
plant-w...](https://www.abc.net.au/news/2019-04-05/solar-thermal-plant-will-
not-go-ahead-in-port-augusta/10973948)

Given that the company website is refusing connections, I think it's likely
dead, which is sad too.

~~~
iagovar
Acciona also sold its assets in Australia to some other companies. It seems
that CSP is no easy business. There are still a few in Spain though.

~~~
taneq
CSP was very competitive 10 years ago before the bottom fell out of the solar
panel market. Solar panels and batteries are now so ridiculously cheap that
it's kind of silly not to just use battery backed PV solar.

~~~
Gibbon1
I went and did a simple cost analysis and CSP is a dead end. A selling point
is that it can store energy as molten salt. But when you run the numbers it's
cheaper to heat the salt with PV solar energy.

The problem is PV silicon wafers have gotten so cheap that rest of the systems
costs are dominating. The difference in costs between a mirror and a PV panel
isn't large. Then add the mechanicals to focus the mirror and the mirror costs
more.

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pfdietz
Concentrated solar (thermal or PV) has not kept up with ordinary
unconcentrated PV. And it doesn't work with diffused sunlight, which the
latter collects just fine.

~~~
mcv
Would it make sense to use ordinary PV cells and use that energy to heat
molten salt to use during the night? Or are there too many efficiency losses
there?

~~~
ZeroGravitas
There's a variety of storage ideas that just use any excess electricity e.g.
Google X's Malta

[https://www.maltainc.com/our-solution](https://www.maltainc.com/our-solution)

There's various prototypes in testing but at least for short term storage I
think lithium batteries continual price drop is leading the pack.

~~~
entropicdrifter
Unfortunately lithium is becoming increasingly difficult to obtain at scale.
If graphite becomes commercially viable, that might be a good step up since
Carbon is freaking everywhere.

~~~
pfdietz
Lithium reserves are more than 100x annual global production. Estimate lithium
resources are something like 600x annual global production. There is no
shortage of lithium, although there are temporary bottlenecks as capacity
ramps up.

------
LoveDeathRobots
"The Crescent Dunes Solar Energy Project .. substantially missed its intended
power production over its four-year lifespan by only achieving about 20% of
its capacity on an annual basis"

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

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adrianN
This is pretty old technology. Right now it's cheaper to build normal PV and
rely on e.g. gas peakers. Eventually we'll want to deploy this, unless
batteries become a lot cheaper.

~~~
Jweb_Guru
Okay. Gas peakers are not a sustainable alternative to renewables, so we're
going to need solutions that cost more.

~~~
adrianN
I suggest we keep building normal PV and wind power until balancing the grid
actually becomes a problem and then switch to more expensive technology. Gas
peakers can actually be sustainable if you feed them with gas from power-to-
gas plants btw. That's a convenient but expensive way for storing large
amounts of power.

~~~
Jweb_Guru
That's not remotely practical and you know it. Let's not pretend that burning
gas is a sustainable approach to power generation, regardless of how it's
generated. I also don't really understand how you think we're going to
suddenly flip a switch when "balancing the grid becomes a problem" if there
are no alternative plant designs that people have actually constructed in
large enough quantities to learn how to do it cheaply. In practice, if new
nations onboarding with solar energy _also_ add gas plants, we use more gas
faster and contribute more to global warming. To me, it's pretty indefensible
not to look at alternatives because they're more expensive.

~~~
kragen
Accusing someone of secretly agreeing with your point of view despite
pretending to believe the opposite does not amount to assuming good faith. Do
you think you could rephrase your comment in a less insulting way?

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vondur
There is one of these on the Nevada-California border outside of Las Vegas. I
know they have had issues with the plant, such as the valley it's located gets
foggy, which lowers the output. What's bad is the concentrated sun rays have
been killing birds from what I've heard. Not sure of any easy way to dissuade
birds from coming near it. It does look really cool off Interstate 15.

------
reallydontask
It would be pretty ironic if we got to the point of too cheap to meter with
renewable based electricity.

I realise that this is unlikely to happen but given the way prices are falling
...

~~~
gwbas1c
> too cheap to meter

I like to joke that electricity is already too cheap to meter; just look at
all the free places to plug in a phone or laptop!

IMO: Energy will never be "too cheap to meter," because someone will always
come up with a way to consume lots of cheap energy.

~~~
throw0101a
> _IMO: Energy will never be "too cheap to meter," because someone will always
> come up with a way to consume lots of cheap energy._

Jevons paradox:

> _Economists have observed that consumers tend to travel more when their cars
> are more fuel efficient, causing a 'rebound' in the demand for fuel.[10] An
> increase in the efficiency with which a resource (e.g. fuel) is used, causes
> a decrease in the cost of using that resource when measured in terms of what
> it can achieve (e.g. travel). Generally speaking, a decrease in the cost (or
> price) of a good or service will increase the quantity demanded (the law of
> demand). With a lower cost for travel, consumers will travel more,
> increasing the demand for fuel. This increase in demand is known as the
> rebound effect, and it may or may not be large enough to offset the original
> drop in fuel use from the increased efficiency. The Jevons paradox occurs
> when the rebound effect is greater than 100%, exceeding the original
> efficiency gains.[5]_

* [https://en.wikipedia.org/wiki/Jevons_paradox](https://en.wikipedia.org/wiki/Jevons_paradox)

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ReptileMan
Any reason we cannot melt the salt the conventional way while using excess
electricity from renewables?

~~~
asdfman123
You mean melting the salt using electricity with excess capacity?

I'm not an expert but I'm guessing we don't do this because the process of
converting heat back to electricity is pretty inefficient. I think I saw
someone say you only capture 1/3rd of the energy when you do that.

However, if you're already starting with heat and need to convert it to
electricity, you can just store it for later conversion.

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mikece
The article mentions that the solar plant produces 110MW, which I presume is
the __thermal __energy captured. On average converting thermal to electric is
about 1 /3 efficient so this two-mile-wide field of mirrors, all of which
require electric motors, maintenance, and regular cleaning for actual
operation, will produce maybe 40MW of electricity? How many megawatts would be
generated if all of those mirrors had PV panels installed instead?

~~~
mixmax
In the daytime - probably more.

In the nighttime - zero.

that is one of the primary points of the system; You can generate molten salt
when the sun is out, and genereate the electricity via a steam turbine
whenever you want.

This gives you the possibility to use this technology as a buffer.

~~~
entropicdrifter
Perhaps a hybrid system would be the best compromise: use PV panels to capture
electricity, but keep some salt molten using a combination of electrical
heating and solar energy redirected off the panels' protective coatings, then
at night you can supplement your batteries with the far longer lasting molten
salt.

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hawkesnest
Missing [2018] tag

