
A $3B Plan to Turn Hoover Dam into a Giant Battery - kpozin
https://www.nytimes.com/interactive/2018/07/24/business/energy-environment/hoover-dam-renewable-energy.html
======
OliverJones
There's a pumped-water electricity storage facility near where I live, called
Northfield Mountain. It entered service in 1972 and has been in use since
then.

When electricity demand is low, the grid operator uses the excess to pump
water uphill. When electrity use is high, the water flows back down into the
Connecticut River. Horthfield Mountain can deliver just over a gigawatt of
energy for eight hours with the generators running at full bore.

It was originally built as a complement to the (now-decomissioned) Vermont
Yankee nuclear power plant. That plant generated 0.6 gigawatts continuously,
and functioned most efficienty if it wasn't ramped up and down to meet
instantaneous demand. So, the storage facility provided a way to vary the
power output from the grid.

The Times piece contained these words:

...utility-scale lithium-ion batteries cost 26 cents a kilowatt-hour, compared
with 15 cents for a pumped-storage hydroelectric project. The typical
household pays about 12.5 cents a kilowatt-hour for electricity.

It's a little misleading. The 26 cents and 15 cents figures are for capital
expenditure to build storage capacity, which can then be used over and over
(for 45 years in Northfield Mountain's case). The 12.5 cents is for a kilowatt
hour consumed.

Also, I fear the 12.5 number represents lazy journalism. The current
residential rate in Los Angeles is 17.8 cents/kWh, and in New York City (home
of the Times) it's 21.0 cents/kWh. Rates vary a LOT geographically.

I hope journalists can learn to understand energy economics better, because
they are a way for the rest of us to learn about them. And learn about them we
must when fossil fuel use diminishes.

~~~
nimos
26/15 is the estimated cost per kwh. Really there is a huge variance,
especially for pumped storage because because of highly variable capital cost.

Capital costs are in the 100s-1000s dollars for kw of pumped storage.[0]

[0][http://large.stanford.edu/courses/2014/ph240/galvan-
lopez2/](http://large.stanford.edu/courses/2014/ph240/galvan-lopez2/)

~~~
ddeck
Similarly for the batteries. If lithium-ion could be had for $0.26/kWh then a
Tesla Model S battery would be $26.

As it stands, Tesla batteries are estimated to be around the $100/kWh level
for individual cells and projected to fall below $100/kWh at the pack level in
a couple of years [1].

[1] [https://cleantechnica.com/2018/06/09/100-kwh-tesla-
battery-c...](https://cleantechnica.com/2018/06/09/100-kwh-tesla-battery-
cells-this-year-100-kwh-tesla-battery-packs-in-2020/)

------
jcranmer
The elephant in the room that I'm surprised wasn't mentioned is that there's
no spare water in the Colorado. The Colorado River Compact allocated more than
100% of the current flow of the Colorado River to the different states (and a
separate agreement adds up Mexico as well too), and it's at the point where a
"good" winter snowpack means that the water level doesn't fall instead of
providing meaningful recharge. The snow in 2016-2017 meant a return to 2014's
low, but 2014 itself saw a miserable 20-foot fall in lake levels that there's
no prospect for reversing. So where will the water to pump into the lake come
from?

~~~
londons_explore
The water is pumped from lower down the river to higher up the river.

No water is lost in the process - you can still use that same water for
feeding almond trees or whatever you guys like to use it for.

~~~
lstodd
First, the water is lost - because evaporation over the large area of the
reservoir only increases with its area, which increases with its level

Second, the scheme decreases flow, and that means level of the downstream.
This means negative effects on ecosystems downstream.

Third, large hydroelectric dams require subordinate downstream reservoirs to
tackle exactly the second problem - keep the downstream flow of the system (of
the two+ dams) at least at some acceptable level to hide the variations in the
main dam's outflow which are due to daily/weekly/monthly/yearly fluctuations
in inflow and power requirements.

Fourth - hydroelectric turbines require some amount of backpressure to
operate. If the backpressure (that is the level of water downstream of the
dam) gets too low, they can't operate unless risking damage. (that's actually
the original reason behind the subordinate downstream dams)

So the project just does not make any sense. Where are they going to get the
water?

~~~
hyperpape
> “the scheme decreases flow”

Can you spell this out in more detail? I would have thought that in the near
future, it would just time shift flow from daytime (when solar production is
high) to nighttime, but perhaps my mental model is over simplified?

~~~
lstodd
The most obvious explanation is that for an unit of power (not energy, mind)
one has to spend a unit of flow (which is unit of volume per unit of time)
falling over a unit of height (which the dam is for).

Now if you pump that unit of flow back up, total downstream loses that same
unit of flow.

Second order effect is that when you pump water back up into the reservoir, it
is evaporating at an increased rate.

Determining the evoparation increase is not trivial, since the reservoir
surface area increases much faster than linear compared to its level at the
dam. If they didn't, the dam would've been that much higher, because
evaporative losses of the future reservoir are a major factor in the design of
the dam.

~~~
hyperpape
I'm only asking about the first order effect (your second point, not your
first). My question was: if you're letting that water back out every night,
don't you get the unit of flow back then? It's delayed by up to 12 hours, but
is that a really big effect?

~~~
lstodd
You have to keep enough water somewhere downstream of the dam for the night so
that you have something to pump up during the day. If you don't, there's
either not enough water to pump up, or severe level fluctuations. If you do,
it requires another dam, evapo losses, etc, etc.

------
delinka
Nit: Lake Mead is the battery. Hoover's generators are extracting power from
that "battery" constantly.

The plan from TFA: Take water that's already passed through the generators at
Hoover and, using solar and wind power, pump it back upstream into Mead to be
processed again. This gives us the ability to supplement hydro with solar and
wind. I guess if this is more efficient than other batteries, it's not a
completely crazy idea. It does, however, have potential negative impact on
downstream ecosystems.

Also: I assume that we don't extract 100% of the available potential from the
dammed water: how much water flows past generators (instead of through them)
and how does that change when upstream water supply changes? How much of a
decrease in this "loss" can we get from this solar/wind plan?

~~~
ridgeguy
At Hoover Dam, 100% of the river flows through the turbines with no bypass.
The dam was originally built for flood control. Power generation is driven by
downstream water demands. [1]

[1]
[https://en.wikipedia.org/wiki/Hoover_Dam#Operation](https://en.wikipedia.org/wiki/Hoover_Dam#Operation)

"The entire flow of the Colorado River passes through the turbines."

~~~
Someone
But it isn’t 100% efficient in converting potential energy into electricity.
Even if the generators were 100% efficient, resistance in the pipes leading to
the turbines slow down the water, not all the water hits the turbine blades,
the water that does doesn’t transfer all its energy (the water would have to
have zero speed after the turbine to do that, and the turbines would have to
be at the bottom water level)

~~~
ridgeguy
Understood.

I took the OP's "how much water flows past generators" to address whether all
the dam's outflow goes through the turbines or whether some is diverted around
them.

The former is the case. The latter only happens when spillways are in use,
which is rare.

------
lucasjans
The political challenges sound immense. The last paragraph in the article sums
it up nicely.

> "The hurdles are minimal and the negotiations simple, as long as everybody
> agrees with Nevada"

Besides the Hoover Dam/Lake Mead, what other large scale energy storage
opportunities exist in the United States?

~~~
mabbo
This might sound insane, but the great lakes might work, with a joint Canada-
US plan. Raising one of them by a foot would be all you'd need because their
area is so huge.

If you're willing to look outside the US, a wild but interesting mega project
might be to try to do the same thing with the South Aral Sea. Pump water all
the way from the Caspian. The North Aral is cut off by a dam/dyke and the
south Aral barely exists anymore, causing major economic harm. Fill it with
salt water and salt water fish to revive the fishing economy while using it as
a giant battery.

~~~
gpm
Niagara falls (Erie -> Ontario) is already a huge hydro eletric power
generator with variable flow. Instead of storing water though they decide how
much water to allow over the falls for tourists. More during the day, less at
night.

Thinking about the terrain, it would probably be relatively easy to setup a
dam somewhere that acted as a battery, downstream is basically already a giant
bowl... I suspect the tourist industry would complain though.

~~~
ulfw
They create more electricity at night when less electricity is generally
consumed? Odd. But interesting.

~~~
londons_explore
They want niagara falls to look great for tourists.

When nobody is looking at night, it pretty much stops.

~~~
Scoundreller
Not only that, but so much water gets diverted during the night that the
tourist ships could not operate.

Reducing water flow helps to preserve the falls too. The water has
substantially changed their shape, even over a time period of 2-300 years:
[https://www.marriottonthefalls.com/blog/2015/02/06/rate-
eros...](https://www.marriottonthefalls.com/blog/2015/02/06/rate-erosion-
niagara-falls)

During the Post-Great Big Blackout period, the Falls power generation ran with
night-time levels of diversion during the day-time. The tourist boats that go
near the falls got furloughed.

------
rkuska
There was an episode on planet money about this.
[https://www.npr.org/sections/money/2018/06/15/620298266/epis...](https://www.npr.org/sections/money/2018/06/15/620298266/episode-848-the-
world-s-biggest-battery)

------
progfix
Pump storage plants are used all over the world for decades, that they are
more efficient than Lithium batteries should surprise no one.

~~~
phkahler
When there is a dam already producing electricity, you just reduce the flow
through the dam rather than pumping the water back uphill. That is by far the
most efficient way to handle excess generation from other sources in this
case. This is a politically driven proposal whose implementation will be a
boon to private producers at the expense of taxpayers.

~~~
redwood
Those generators and flow valves likely cannot respond quick enough to the
momentary power surges

~~~
snowwindwaves
A hydro turbine on a dam with no penstocks can probably go from 0-100% in 5 to
10 seconds.

The limit is pressure waves in the water conveyance system due to changes in
flow through the turbine. If the water conveyance system is only the width of
the dam and encased in concrete it is going to have minimal transients
compared to a 7km long steel or HDPE penstock on which the time from 0-100% is
more like 2 minutes

------
envoked
After moving to the Columbia Gorge I became fascinated with the dams and
energy production on the Columbia. Over the last 75ish years the whole river
has been turned into a battery through a series of dams and reservoirs. The
scale is astonishing - Grand Coulee itself produces ~6800 megawatts (about 3x
of Hoover Dam).

For those interested [A River Lost: The Life and Death of the
Columbia]([https://www.amazon.com/River-Lost-Life-Death-
Columbia/dp/039...](https://www.amazon.com/River-Lost-Life-Death-
Columbia/dp/0393316904)) is a great book documenting the creation and long
term implications (from cheap electricity for the Manhattan Project, to
agriculture, to the collapse of the Salmon population) of the project.

------
pwagland
Despite that this was submitted four hours earlier than
[https://news.ycombinator.com/item?id=17637437](https://news.ycombinator.com/item?id=17637437)
, that one has more comments, at least at the moment.

------
simonswords82
Duplicate of this
[https://news.ycombinator.com/item?id=17637437](https://news.ycombinator.com/item?id=17637437)

------
thezilch
NPR's Planet Money recently had a good story about alternatives to traditional
batteries in "#848 The World's Biggest Battery"
[https://www.npr.org/templates/transcript/transcript.php?stor...](https://www.npr.org/templates/transcript/transcript.php?storyId=620288114)

------
booleanbetrayal
The Bath County Pumped Storage Station has been doing a similar thing since
'85 and can be characterized as the largest battery in the world.

[https://en.m.wikipedia.org/wiki/Bath_County_Pumped_Storage_S...](https://en.m.wikipedia.org/wiki/Bath_County_Pumped_Storage_Station)

------
microtheo
A similar project has been on construction in Europe
[https://de.m.wikipedia.org/wiki/Nant_de_Drance](https://de.m.wikipedia.org/wiki/Nant_de_Drance)
Cost of $2B. I had the chance to visit the caverne where the turbines will be,
really amazing engineering!

~~~
rurban
Pump storages are already all over Europe for decades. The most famous one
being Kaprun/Austria, built by the Nazis in the 30ies. They are all over the
Alps, as the green party lets them.

Those pump storages provide the very expensive peek electricity all over
Europe, needed for the spikes in the morning and noon.

Nevada probably didn't need it back then, Hoover Dam was built for flood
protection, and since then the levels are too low to work efficiently as pump
storage. But since peek energy is in high demand they think it over.

------
IloveHN84
Looks like the real version of Fallout universe imagined by Bethesda

~~~
ksdale
Many of the Fallout games are indeed set in the western half of the US :)

~~~
lfowles
And specifically Hoover Dam appears in New Vegas.

~~~
HNNewer
yeah an the quest focuses on activate energy from Hoover Dam :)

------
hn_throwaway_99
The article says the desired pumping station would be located 20 miles
downstream from the dam. Why would it need to be so far?

~~~
progfix
My guess is to get an economically height difference to the dam.

~~~
phire
No, any extra height to pump water up compared to the height of the dam is
just wasted power. They wouldn't do that without a good reason.

My understanding is you can't just stick an inlet on the river, otherwise you
could only pump water up when the dam was running (defeating the point). You
need to build some kind of reservoir.

Additionally, with hydropower it's not enough to build a dam above your
generators. You also need to get rid of the water exiting your generators fast
enough. If there is any restiction on the outflow, the back pressure will
decrease the generation capacity.

My guess is the distance is needed to meet these requirements. Enough space to
let the water slow down, then enough space to build a reservoir.

~~~
progfix
Why would it be wasted power? Height difference = stored potential power. I
was talking about that maybe 20 miles downstream the pump-size/-energy
consumption to stored power is more efficent.

~~~
phire
Because the height difference that matters is the difference between the water
level in the lake and the turbines.

If your pumping station inlet is 20m below the turbines, then any energy used
pumping water upto the height of the turbines is wasted, because it can't be
recovered when the water comes back down.

------
phkahler
This seems incredibly stupid. If you use excess electricity to pump water
backward at the dam, you may as well just shut off the flow through the dam
instead. That would be more efficient and cost nothing to implement.

If we're talking about so much excess capacity that the dam would be closed
AND water pumped back up, that would be interesting. But wouldn't the river go
dry? It's not like there's a lake below the dam for that.

This whole thing seems more political than practical. I'm guessing the private
producers will somehow get a financial benefit from this at the expense of the
taxpayer.

~~~
maxerickson
It depends an awful lot on the lag between demand and excess supply. It might
use the noon sun to pump water that was used to meet morning demand.

~~~
phkahler
>>It depends an awful lot on the lag between demand and excess supply. It
might use the noon sun to pump water that was used to meet morning demand.

You could just shut off the dam at noon instead. Then run it full tilt in the
morning.

~~~
UncleEntity
They can't just "shut off the dam at noon" because of all the downstream
users, a dry river bed isn't much of a tourist attraction.

~~~
Dylan16807
A pump causes the exact same problem, except a few miles downstream.

