
A solar power researcher discusses the “duck curve” he helped discover - curtis
https://www.vox.com/energy-and-environment/2018/3/20/17128478/solar-duck-curve-nrel-researcher
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chis
_David Roberts

When you curtail the coal plant, though, you still have the fuel. You’re not
wasting it.

Paul Denholm

But what fraction of the LCOE [levelized cost of energy] of a mine-mouth coal
plant is the fuel? It’s a small fraction. The cost of the plant is the major
component of the LCOE, so when I curtail generation from that coal plant, I’m
losing the opportunity to recover the cost of investing in that really
expensive asset._

I never considered that running a coal plant below capacity is the same as
dumping solar panel energy, economically speaking.

~~~
Retric
Yea, this is vastly better than most discussions of the topic.

Talking about seasonal storage is kind of silly costs are low enough that you
can build say 20% more solar and wind than you need on average and they are
still cheaper than gas/nuclear/coal. On top of that hydropower is very
dispatchable which acts a lot like seasonal energy storage because you are
storing months worth of river flow.

~~~
jaggederest
I'm just thinking of fun ways to build businesses around dispatchable, quick-
ramping energy sinks that could serve in lieu of curtailment.

Obviously energy intensive businesses like aluminum smelting, chemical
production, etc, but also things like refrigeration units running slightly
more midday to produce chilled water and then idling until ~10pm, battery
backups at datacenters being half way drained and then refilled off-peak, etc.

~~~
nate_meurer
This is a significant element of DR (demand response). Domestic waters are
another attractive target, and there some pilot programs around the U.S.
fleshing out the details.

~~~
nate_meurer
Sorry, that should read "domestic water heaters"

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brandmeyer
> We’re just going to need the right intelligence in the system, sending the
> right economic signals [i.e., charging varying rates throughout the day,
> more when power is expensive, less when it is cheaper].

Hell. Yes.

Most of the deregulated markets already have a futures market price scheduled
in 15 minute intervals that clears 24 hours in advance. Expose end customers
to that day-ahead market and we can get all kinds of flexibility.

~~~
sounds
I am cautiously optimistic that varying rate schedules will help.

It is unfortunately true that most residential users will not pay enough
attention to either curtailing their own use or -- and I think this is the big
one -- shenanigans by the electric utility.

If the result is an effective rate hike, residential users will oppose it.
It's not even that hard to get residential users to love it, but it seems no
one is interested in solving that problem.

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hyperpallium
funfact: the sun is just as bright at dawn and dusk as midday (though, lateral
atmosphere blocks more UV-B). The dip in the duck's back is because the angle
of incidence changes.

Facing solar panels towards the sun throughout the day, to maintain the angle
of incidence at the same as midday (i.e. 0°) flattens and lengthens the demand
curve.

This sun-tracking is important, not to maximize power output, but for this
effect on the demand curve, reducing storage and grid need.

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eksu
They should do dynamic pricing throughout the day and then there would be a
market for users to use smart devices to schedule load, when to charge
batteries vs when to discharge batteries, etc.

~~~
tantalor
Pump all the water up hill.

~~~
HankB99
I wonder if that was a tongue in cheek comment or if you knew this is already
done.
[https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power...](https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power_Plant)

~~~
maxander
My goodness- built in the sixties, stores several GWh, and has 70% efficiency.
Enough of those would solve the curtailment problem altogether.

Not sure how a technology that relies on the availability of titanic
quantities of fresh water is going to play out in California, though. :(

~~~
jaggederest
It doesn't need to be fresh, you could dam a certain bay and put
generator/pumps in the wall. Pump a cubic mile of water back and forth as
needed, and you get tidal generation for free, too.

~~~
milesvp
Tidal generation using dams is a _very_ bad idea. You're taking energy from
and releasing energy to the system at times when it's most detrimental to the
inertia of the system. Basically you're stealing inertia from the rotation if
the earth, which would be ok, except you're amplifying the effects because of
timing. You can think of it like swinging in a swing. The way you build up a
huge amount of momentum is by shifting your weight at the peaks and troughs of
the arc.

~~~
jaggederest
All hydropower does this, and changes the rotation of the earth. I believe the
stated value was speeding the rotation up a few milliseconds per day due to
the fact that so much water is held in the northern hemisphere in reservoirs.

The ultimate result is that the moon falls towards the earth a couple
micrometers and everything is fine.

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neverdark
For anyone interested in this topic, I’d highly recommend checking out some of
the papers by Denholm. His papers are usually quite approachable, but very
thorough and well written.

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csense
I'm disappointed he didn't say anything about the frequency stabilization
issue.

A system based mostly around turbines has the inertia of thousands, maybe
millions of tons of spinning metal across the entire grid, which buffers
enough energy for control systems (for example controlling how much fuel to
inject) to respond to sudden demand changes while maintaining stability.

If everything's solid-state solar, following demand is harder.

~~~
ghouse
The term of art is "frequency response" for "stabilization." This is the
system's ability to respond to shocks. Though, the need for frequency response
is driven primarily by very large "traditional" power plants. For example, in
WECC, the single largest contingency is the loss of a 4GW large nuclear
complex. So, should the cost of maintaining this frequency response be borne
by the system, or by that specific contingency? Smaller power plants, and
smaller transmission lines have smaller contingencies.

Following demand is a different function called frequency regulation.
Regulating frequency down (curtailing output) is easy for solid-state
inverters (including solar), though regulating up (increasing output) is, as
you note, more difficult for generation (but very easy for load).

------
ZeroGravitas
The headline and intro have much more drama than the interview with the
expert.

------
ghouse
For those interested in seeing the California "duck curve" in real time, the
CAISO publishes it here:
[http://www.caiso.com/TodaysOutlook/Pages/default.aspx](http://www.caiso.com/TodaysOutlook/Pages/default.aspx)

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dchichkov
Strange. I'm looking at major California provider plans -
[https://www.pge.com/en_US/residential/rate-plans/how-
rates-w...](https://www.pge.com/en_US/residential/rate-plans/how-rates-
work/find-my-best-rate-plan.page)

And the peak time (and pricing) is 3 p.m. to 8 p.m. PG&E recommends to "shift
usage to the least expensive hours: before 3 p.m. and after 8 p.m. every day".

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Jedd
I wonder why solar thermal isn't considered as a partial solution -- in terms
of providing power well after sunset, and thereby flattening out that evening
peak.

~~~
ghouse
It is considered a partial solution. There are large solar thermal power
plants that can store heat in the form of molten salt, and then later using
that heat to flash water to steam to spin a turbine.

However, this is, in most scenarios today, more expensive than simply spinning
up a combustion turbine to provide power well after sunset.

~~~
stergios
Areva Solar sells thermal power plants where the working fluids are oil and
water. A challenge with solar thermal is the lower working temperature and
pressure, and the inability to drive traditional size power turbines
efficiently.

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keebEz
For new technologies, adoption curves can vary wildly, and for different
reasons. When it comes to clean tech, PV and wind specifically, the adoption
is dominated by sunsetting investments over a long horizon.

Other types of tech have much faster adoption cycles due to the lower cost of
substitution. For each peak-hour kWh from PV comes at an increased cost of
non-peak-hour kWh from non-PV (whether storage or generation).

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kumarvvr
I hope we can find an efficient way to store solar energy. That will solve
many problems with solar power generation.

Lithium ion batteries can only do so much. On a global scale, they are too
small to have a meaningful impact.

~~~
ghouse
They already have a meaningful impact today in the eastern US. In the PJM RTO,
batteries (and fly wheels) perform frequency regulation (discussed elsewhere
in these comments).

~~~
dragontamer
Frequency regulation is measured in minutes of storage though, not hours.
LiIon / Flywheels are great to store minutes of energy cheaply. In effect,
LiIon / Flywheels are hundreds-of-MW-hrs size at best.

But unfortunately, the sun disappears for hours. A bigger solution is needed.
Pumped hydro works for sure, but even at GW-hr scale (and yes, there are
pumped-hydro plants at GW-hr size), its not going to be enough.

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legohead
Do most solar installations not include batteries?

~~~
ghouse
No, most do not. This is true for both utility projects and retail (behind the
meter) projects. However, with the falling cost of batteries, and shifting
price signals in the market, this is beginning to change -- in Germany, the
US, and Australia primarily.

Utilities in the US have been changing their rates (tariffs) to decease the
cost of energy (kWh), but increase the cost of demand (kW) as a way to
(dissuade solar adoption / align cost of service -- depending on your
perspective). But within increased demand charges, this permits batteries to
offer more value than shifting the time of use of energy.

~~~
francisofascii
Utilities are also increasing customer changes while keeping kWh charges low.

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nthompson
Isn't this problem caused by fix axis solar? If all solar panels were on
trackers, wouldn't the curve change form and partially mitigate the problem?

~~~
wtallis
Better tracking of the sun won't significantly increase production at noon,
but could help with mid-morning and mid-afternoon production. But that only
makes the duck curve steeper, and the existing infrastructure needs a smoother
curve.

~~~
nthompson
I imagine both steeper and flatter. The flatter curve seems to be easier to
handle within my naive mental model of how utilities work.

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nrook
I dunno, this so-called expert sounds like a quack.

