
Arizona solar plant achieves six hours after sun goes down - bromagosa
http://phys.org/news/2013-10-arizona-solar-hours-sun.html
======
antr
I worked on this CSP project back in 2009 when it was still on paper. It's
really exciting to see forecasts/estimates/hypothesis that do work out i.e.
store heat energy to serve peak hours when the sun isn't shinning. More
importantly, and what I really look forward to, is that this carbon-free
technology is to a large extent "validated" meaning that this kind of projects
are now less risky, more viable and financeable. Hopefully this will push down
the price of CSP + storage, which will make it more attractive to both utility
incumbents and new entrants/energy startups.

~~~
ndonnellan
I'm curious, what are you doing now? Still in CSP? The projects I worked on
haven't yet come to light (ha), which is a bit disappointing.

~~~
antr
I'm now doing the startup thing, but not in the energy space.

~~~
ndonnellan
Ditto, xP. Although, I imagine in 5-10 years solar will be a big player in
energy, so I'm trying to stay current. Just gotta make it through the next
5-10 years.

------
Lagged2Death
I've been puzzled for some time: Is anyone / why isn't anyone working on more
flexible and responsive coal and nuclear plants? Instead of storing renewable
energy, it would be more efficient, less complex, and less capital-intensive
(one would think) to consume the renewable energy immediately and make up the
difference between supply and demand with flexible traditionally-fueled
plants.

I'm sure there's a good reason. I just don't know what it is.

~~~
DougWebb
By flexible, do you mean "able to ramp up to meet demand and ramp down when
not needed"?

Any power plant that uses steam turbines is going to have a long ramp-up time
to boil a huge quantity of water needed to produce the steam. Nuclear plants
do this, and I imagine most/all coal plants do as well. Hydroelectric plants
don't need to because the falling water drives the turbines directly.

The first thing I thought of when I read the article is that this power plant
can't be very efficient. It's using steam turbines, but six hours after sunset
there isn't enough heat to keep the turbines going. That means they need to
reheat every morning. It seems like it would have been better for them to
include a coal plant for nighttime operations to keep the steam boilers hot
and keep the turbines going all night. That would be flexible, because the
coal burners could start up quickly to keep the already-hot water boiling.
(Can't use nuclear this way because you can't really turn a nuclear reactor on
and off.)

I'm totally guessing here, but I suspect they didn't include an alternate
nighttime operations fuel because this is a "100%-Green" project that either
wouldn't have gotten funding if there was a coal plant involved or it was just
intended as a demonstration of the solar capability and didn't need to be
practically efficient.

~~~
tracker1
There's also a given that 6hrs after sunset there isn't a need for as much
power... most of the population is asleep, lights off, TVs off, etc. There are
other traditional power plants (Hydro and Nuclear) in AZ that provide overflow
service for off hours. It actually takes a combination of plants to offer the
best load distribution.

In parts of AZ there are serious brown outs and rolling blackouts in the
summers as A/C kicks in everywhere, which is probably the biggest draw.

I'm opposed to coal altogether for pollution reasons alone. It's bad enough
between the cars and airport traffic, don't need more.

~~~
nearengine
Do you have any kind of source on that? I've lived in Arizona all my life, and
the only rolling brownouts I've experienced and heard about have been in
California. Who I believe already buy _surplus_ power from AZ.

~~~
tracker1
I lived in Prescott Valley, and several years in a row saw brown/blackouts in
mid-summer. Also saw them a number of times in the Peoria & I-17 area in phx
(closer to cactus)

~~~
nearengine
I've seen outages lasting a couple hours from components like transformers
breaking, but that's a different issue from the grid itself not producing
enough power to meet demand. Can't speak for Prescott Valley though.

Interestingly, the only article on a Phoenix area blackout due to high load I
was able to source happened in the winter... probably caught SRP totally off
guard:

[http://www.azfamily.com/news/local/Rolling-blackouts-
sparked...](http://www.azfamily.com/news/local/Rolling-blackouts-sparked-by-
cold-weather-in-Arizona-115117204.html)

------
TheCraiggers
I find it interesting that we're still using water to transfer the energy. Has
there been much research into finding better ways to create electricity than
stream => turbine? Is there anything interesting happening in this area?

It just seems to me that the process of turning water to steam to impart
kinetic energy to a turbine is incredibly wasteful, and all we seem to be
researching are fancier turbines. I would love to be shown otherwise.

~~~
comicjk
It is not all that wasteful; the water is recondensed from the steam so that
when you boil it again it is already quite hot. This process is 1/2 to 2/3 as
efficient as the theoretical maximum efficiency of any possible device, (hot
temp - cold temp)/(hot temp). The difference is mostly materials science - we
don't have any materials strong enough and heat-resistant enough to operate
the cycle at thousands of degrees. But people are certainly working on it.
There is more in universities and in labs than is dreamed of on Hacker News.

------
sergiosgc
Is this a big deal? Molten salt plants have achieved almost a day with no sun.
Example: [http://www.torresolenergy.com/TORRESOL/gemasolar-
plant/en](http://www.torresolenergy.com/TORRESOL/gemasolar-plant/en)

~~~
cinquemb
I think it is a bigger deal for people who haven't been following CSP tech
these past couple of years.

------
d4nt
This is a big deal, one of the key benefits of Coal/Gas/Oil power stations is
their ability to provide frequency response (where the power output is
adjusted to keep the AC as close to 50 Hz as possible) or to participate in a
balancing mechanism (where generators place bids on providing minute by minute
changes to their power output). Until now the only thing a solar/wind/nuclear
generator could do was turn their generators on or off. That severally limits
the proportion of renewables you can reasonably have on your grid[1]. But this
technology looks like it'll give a renewable generator a way of dynamically
adjusting their output to match demand.

[1] You do get controlled generation with biomass, but the efficiency is
terrible and you need that land to grow food, so it'll (hopefully) only ever
be a niche technology.

~~~
maxerickson
Biomass generally means wood or agricultural waste/residue. Tree plantations
probably use some land suitable for farming, but not all that much.

Most biomass generation occurs at plants that have other operations involving
wood, so even much of the wood burned is byproduct.

I agree that massive expansion of biomass generation would impact agricultural
land.

~~~
Cthulhu_
> I agree that massive expansion of biomass generation would impact
> agricultural land.

It would; just look at the amount of farmland currently used to produce plants
used for the production of biofuels. It's a big impact on the food production
capacity of the world, and it's mainly used to mix with regular oil-based
fuels so that the oil/gas companies adhere to government standards, tax
reductions and customer goodwill, whilst the biofuel producers get government
grants and fundings and more tax deductions.

Of course, that's (iirc) first-generation biofuel, second/third generation (or
grade) biofuel uses biowaste (shells, green stuff, animal waste, stuff that
would otherwise be processed into compost or fertilizer).

source: my memory

------
zackmorris
3 square miles is 7.77 square km. Just over 1 kW of sunlight falls per square
meter, so I will round up and say that there are 8 GW falling on the plant
total.

 _So 280 MW of production is 3.5% efficient of peak irradiance._

BUT average irradiance is smaller than peak:

[http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook...](http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/)

It looks like 5 kWh/m2 for Arizona, so that's 38.85 GW per day irradiance on
7.77 sq km. Assuming the plant can put out its maximum capacity for the 18
hours it runs each day, that's 280 times 18 = 5 GW per day.

 _So it 's operating at almost 13% efficiency of average irradiance._

That is very good, considering that they are able to store heat much more
cheaply and environmentally friendly than storing electricity in batteries.

The most important thing of all is that it doesn't have to wait for
innovations in photovoltaics. Anyone can buy land, set up parabolic mirrors,
and tinker with forgotten heat engines like Stirling cycle engines or Tesla
turbine engines that easily achieve 30, 40, 50% efficiency and approach the
Carnot limit. Conversion of motion to electricity is a solved problem at 95%
efficiency.

Oh and these plants can be supplemented by biomass, say biodiesel from algae
or fuel pellets made of hemp. If that's too granola for the fossil fuel
industry, they can also use natural gas.

In fact if you study this long enough, you find that there are only two real
hurdles: energy storage and connection to the grid (made difficult because of
resistance from established utilities). Generation turns out to be relatively
inexpensive because there's a sea of free energy all around us. To put it in
perspective, Grand Coulee dam puts out less power than the irradiance falling
on the solar plant. It's just more efficient at converting the motion of
falling water to electricity:

[http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p...](http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations)

It puts out 6.8 times 24 = 163 GW/day. That's 33 of these solar plants. So
every 100 sq miles (260 sq km) of desert is equal to the 324 sq km of area
flooded by Grand Coulee.

Solar thermal is the hydroelectric of the future and uses less land, which
will only improve going forward. IMHO this will someday dwarf wind and nearly
eliminate intermittency issues.

~~~
cataflam
> (...) that's 280 times 18 = 5 GW per day. (...) > (...) It puts out 6.8
> times 24 = 163 GW/day. (...)

GW (GigaWatt) is already energy over time (Joules per second), you don't
multiply it by the number of hours a day (why hours, why not seconds or
anything else for example). Unless you're counting multiple plants you're
adding, but that's not the case here.

edit after finishing this post: actually, you seem to be using W(att) for both
W (watt, a unit of power) and Wh (Watt-hour, a unit of energy), which, besides
being wrong, leads to confusion. Your post is very coherent under this new
light.

So this :

> It looks like 5 kWh/m2 for Arizona, so that's 38.85 GW per day irradiance on
> 7.77 sq km. Assuming the plant can put out its maximum capacity for the 18
> hours it runs each day, that's 280 times 18 = 5 GW per day.

Actually becomes :

5 kWh/m² _/ day_ -> 5/24 kW/m² (since there are 24 hours a day and a kWh is
the energy of 1 kW power over 1 hour), so 7.77 x 1000000 x 1000 x 5 / 24 Watt
= about 1.6 GW for 7.77 km².

And assuming the plant can run at 280 MW for 18 hours per day, its average
power output is 280 x 18 / 24 = 210 MW.

~~~
zackmorris
Unfortunately I'm unable to edit my post now because it's too old. For anyone
finding this, cataflam is partially right, I had some typos but the math is
the same. I stand by using total power output per day to calculate
efficiencies. cataflam's right that over a 24 hour period, you could say the
average output would be 210 MW. Here is the corrected version:

\---

3 square miles is 7.77 square km. Just over 1 kW of sunlight falls per square
meter, so I will round up and say that there are 8 GW falling on the plant
total. 280 MW over 8 GW = 0.035.

 _So 280 MW of production is 3.5% efficient of peak irradiance._

BUT average irradiance is smaller than peak:

[http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p...](http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations)

It looks like 5 kWh per m2 per day for Arizona, so that's 5 kWh per m2 times
7,700,000 sq m = 38.85 GWh per day irradiance on 7.77 sq km. Assuming the
plant can put out its maximum capacity for the 18 hours it runs each day,
that's 280 MW times 18 hrs = 5 GWh per day. 5 GWh over 38.85 GWh = 0.1287.

 _So it 's operating at almost 13% efficiency of average irradiance._

That is very good, considering that they are able to store heat much more
cheaply and environmentally friendly than storing electricity in batteries.

The most important thing of all is that it doesn't have to wait for
innovations in photovoltaics. Anyone can buy land, set up parabolic mirrors,
and tinker with forgotten heat engines like Stirling cycle engines or Tesla
turbine engines that easily achieve 30, 40, 50% efficiency and approach the
Carnot limit. Conversion of rotational motion from a turbine to electricity
with a generator is a solved problem at 95% efficiency.

Oh and these plants can be supplemented by biomass, say biodiesel from algae
or fuel pellets made of hemp. If that's too granola for the fossil fuel
industry, they can also use natural gas.

In fact if you study this long enough, you find that there are only two real
hurdles: energy storage and connection to the grid (made difficult because of
resistance from established utilities). Generation turns out to be relatively
inexpensive because there's a sea of free energy all around us. To put it in
perspective, Grand Coulee dam puts out less power than the irradiance falling
on the solar plant. It's just more efficient at converting the motion of
falling water to electricity:

[http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p...](http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations)

It puts out 6.8 GW times 24 hrs = 163 GWh/day. That's 33 of these solar
plants. So every 100 sq miles (260 sq km) of desert is equal to the 324 sq km
of area flooded by Grand Coulee.

Solar thermal is the hydroelectric of the future and uses less land, which
will only improve going forward. IMHO this will someday dwarf wind and nearly
eliminate intermittency issues.

------
jwcacces
So, does it take 6 hours to heat up in the morning?

~~~
phaemon
No. To be honest, I was a bit baffled by your question: why would you think
that it would take the same time to heat as to cool?

It will heat depending on how quickly you can get energy to it, and it will
cool depending on how quickly you can remove energy from it. Have you never
seen an electric heater or oven and noticed they heat quickly and take a while
to cool down? Or rapidly cooled something by putting it in iced water or a
freezer?

~~~
mpyne
> I was a bit baffled by your question:

There's nothing to be baffled about, it's a fair question. You even provided
the answer: "It will heat depending on how quickly you can get energy to it,
and it will cool depending on how quickly you can remove energy from it."

On the other hand, there's no "electric heater" here to use to heat up the
liquid used to absorb solar heat (not to mention ice or freezers...); it's the
sun or nothing. Given that the sun doesn't give us peak solar flux until the
midday it's entirely possible that solar energy production in the first few
hours of the day would only keep up with instantaneous energy needs instead of
having enough of an excess to reheat the heat storage fluid for energy
production later that night.

Whether this is actually an issue or not depends on the numbers, but it's not
a baffling question at all and there's no reason to be so condescending about
it.

~~~
phaemon
It's baffling to me because it makes no sense based on everyday experience to
think that things have a set amount of time that they heat up or cool down.
Why would anyone think that?

If you think my comment was condescending, stop reading it in a condescending
tone.

------
pkulak
I assume this is a molten salt plant? If so, I didn't think that was a new
thing because I've heard about it plenty before now. Is this the largest
solar-thermal plant doing this? The first?

~~~
phorese
_" In addition to creating steam, the heat transfer fluid is used to heat
molten salt in tanks adjacent to the steam boilers. The thermal energy storage
system includes six pairs of hot and cold tanks with a capacity of 125,000
metric tons of salt, and the molten salt is kept at a minimum temperature of
530 degrees Fahrenheit."_

(link at bottom of OP's article)

------
quarterto
That headline feels like they accidentally a word.

------
jzwinck
The aerial photograph at the top of TFA looks a whole lot like SimCity[1].
Awesome.

[1] One of the old versions, not the 2013 one nobody plays.

~~~
_mulder_
"not the 2013 one nobody plays"

Haha, so true. But ironically on the 2013 one you can actually build a massive
solar farm that will look just like that.

