

Molten Aluminum Lakes Offer Power Storage for German Wind Farms - sveme
http://www.bloomberg.com/news/2014-11-27/molten-aluminum-lakes-offer-power-storage-for-german-wind-farms.html

======
ThePhysicist
The article is really misleading: If I understand correctly, what Trimet will
do is to REDUCE its power consumption on demand in order to reduce the stress
on the power grid at times when there's not enough energy available for
everyone. Since Trimet alone consumes about 0.7 % of Germany's energy
production, adapting its energy consumption can help a lot to stabilize the
power grid. Here's an article that makes this a bit more clear:

[http://www.renewablesinternational.net/german-aluminum-
firm-...](http://www.renewablesinternational.net/german-aluminum-firm-rescues-
grid-twice/150/407/82143/)

The general term for this is "demand response":
[https://en.wikipedia.org/wiki/Demand_response](https://en.wikipedia.org/wiki/Demand_response)

The author of the Bloomberg article seems to think that they will use the
Aluminium as a battery, releasing energy back to the grid, which to my
understanding is not at all what they are planning to do (or even possible,
for that matter).

BTW, a Businessweek article seems to get this wrong as well:
[http://www.businessweek.com/articles/2014-11-26/germanys-
tri...](http://www.businessweek.com/articles/2014-11-26/germanys-trimet-
aluminium-turns-smelting-tanks-into-batteries)

~~~
sveme
It's really a badly written article about an interesting topic - and I'm not
sure what the real story is. Considering the graphic:
[http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_...](http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_630.jpg)
it looks like they are indeed releasing energy back to the grid.

Additional article: [http://www.aluinfo.de/index.php/gda-news-en/items/trimet-
dev...](http://www.aluinfo.de/index.php/gda-news-en/items/trimet-develops-
virtual-electricity-storage.html)

It looks more like they are adapting the process to handle energy
fluctuations. The current process most likely requires a steady current and
they are adapting the process to ramp up during times of cheap energy and
throttle it during times of expensive energy. Still no battery, more like a
balancer, adaptively throttling energy consumption.

 __Edit __

More information from a paper abstract [1]:

High Frequency Power Modulation - TRIMET Smelters Provide Primary Control
Power for Stabilizing the Frequency in the Electricity Grid

Scope The strong growth of renewable energy in Germany leads to high prices
fluctuations, varying with the availability of these energy resources. To deal
with this situation, TRIMET is using the tool “power modulation” since 2008 to
compensate these strong price effects. Simultaneously the strong growth of
renewable energy sources leads to a need of primary regulation energy for
stabilizing the electricity grid at 50 Hz. In this context, TRIMET is the
first electricity consumer world wide, which provides primary regulation
energy by modulating a consumer. Traditionally this source of energy is only
provided by power plants or energy storage plants, e.g. pumped energy storage
or stationery batteries.

[http://www.programmaster.org/PM/PM.nsf/ApprovedAbstracts/281...](http://www.programmaster.org/PM/PM.nsf/ApprovedAbstracts/281A8D0A5E4E0F0085257A48004DD9DA?OpenDocument)

Now were getting closer to the real thing.

Edit II [2]:

TRIMET Aluminium SE is developing a process that can turn electro- lytic
furnaces for the production of primary aluminum in collabora- tion with
conventional power plants into energy storage reservoirs for renewable energy.
Aluminum has a high energy density. This makes its production energy-intensive
and aluminum smelters re- cipients of base-load electricity. Excess energy is
stored in the light metal. The principle behind the new process is the grid-
commutated operation of the production equipment. To ensure this, the
electrolysis cells are modified so that their output can be increased or
reduced for several hours, as needed. The ope- rating point is selected in
such a way that the output can be raised or lowered by more than 25 percent
for hours. This makes it possible to provide enormous storage capacity. Using
this method, TRIMET aluminum smelters could provide outputs of up to 130
megawatts with future capacities of up to 6,000 megawatt hours. This
corresponds to the daily energy consumption of two million people.

The “virtual battery” relies on the improved flexibility of aluminum elec-
trolysis. With this method, TRIMET is revolutionizing the basic principle of a
manufacturing process that has existed for more than 120 years. An
electrolytic furnace is similar to a water container whose walls are made of
ice. To ensure that the tank does not melt, the ambient temperature must be
kept very low. But it must not reach a temperature that is too cold, or the
water in the tank will freeze. Similarly, the temperature of the electrolytic
furnace must be harmonized in order to stabilize the fur- nace walls under
fluctuating power supply levels. The process developed by TRIMET regulates
this balance through the clever use of exhaust heat, a form of thermal
insulation that can be adjusted in an innovative way.

The process offers significant advantages over other storage systems. At 85
percent, the efficiency factor of the aluminum storage reservoir approaches
that of pump storage reservoirs, far higher than those of compressed-air or
hydrogen storage reservoirs. what’s more, the system does not require new
power lines, since it is integrated into the existing high-voltage grid.

[2] [http://www.trimet.de/fileadmin/pdf/trimet-at-a-
glance-2013.p...](http://www.trimet.de/fileadmin/pdf/trimet-at-a-
glance-2013.pdf)

~~~
vilda
Nope, they don't release energy as such, just "resell" it. They buy and
consume energy when it's cheap, then they sell it at higher price by not using
it.

That's why they call it "virtual".

------
Mithaldu
The original german presentation of this is here:

[http://www.innovationsforum-energiewende.de/wp-
content/uploa...](http://www.innovationsforum-energiewende.de/wp-
content/uploads/2013/11/Thomas-Flesch-Trimet.pdf)

To put this in simple terms:

Normally the plant runs at a constant rate of energy consumption, due to
restrictions in how the production process works.

This means sometimes there will be a deficit of available electricity, other
times there will be a surplus.

They plan to change their production process such that they can:

1\. soak up the surplus usefully when it is present

and

2\. "give back" energy to the grid by reducing their own consumption when
there is a deficit

They never feed back any energy, they just make it so more energy is available
on the grid by reducing their own consumption.

The difficult part here is that there is a certain engineering effort
necessary to make this possible in the first place without disrupting the
production process.

~~~
jpfr
Some years ago Germany "deregulated" its energy sector. The energy providers
are buying and selling electricity on exchange markets where prices change
with supply and demand.

Today, industrial clients are changing to dynamic pricing schemes instead of
fixed price-per-kWh contracts with a supplier. That means they also schedule
their consumption to profit from low prices when supply is high and demand
low.

In the future, big industrial clients could take an even more active role on
the energy markets and directly trade capacity without an energy supplier as
intermediary. Germany invests a lot in the grid infrastructure to enable more
flexibility and decentralized energy sources without risking black outs. They
have to do so, as it was politically decided to phase out all nuclear power
plants after Fukushima happened. But it's not easy since nuclear plants
provide a very stable "supply base" whereas the rising renewables are more
volatile.

------
dredmorbius
This is _NOT_ an energy storage system.

It's a demand-dispatch system.

Think of it this way: in a conventional fuel-driven grid, your _generation_
(supply) is dispatchable. If you need more electrical generation, you can
crank up your coal, oil, gas, or nuclear-fueled generators (or hydro capacity)
to meet that demand. Since demand is largely predictable based on known
parameters (weather, day of week, season), even slow-to-cycle generation
(e.g., coal and nuclear) can offer pretty good demand-matching, with the
difference made up by other options. Gas and hydro can respond to load shifts
in seconds to minutes, vs. hours for the others.

Under a largely renewables scenario, your generation is _not_ dispatchable.
Your options are:

⚫ Retain some dispatchable capacity: hydro (conventional or pumped storage),
biofuels, synfuels, geothermal, nuclear, conventional fossil fuels.

⚫ Utilize storage. Batteries, thermal energy storage, banked capacity (e.g.,
excess heating or cooling utilized later), pumped hydro, compressed air energy
storage (CAES), flywheels, capacitors, electricity-to-fuel. All have
limitations, most are cost-prohibitive.

⚫ Load shifting. This generally goes by the terms "demand response" or "demand
side management". Effectively it's the inverse of the present model: rather
than shift supply to meet demand, you're shifting demand to meet (an
inelastic) supply. Typically this involves large industrial uses and
customers.

Tino Andeson's reporting here is horrible. It's sadly all too commonplace in
general coverage of energy issues.

~~~
bryanlarsen
It's a horrible article, but it certainly does imply that it is an energy
storage system.

"The electrodes, in tandem with the liquid metal that settles to the bottom of
the tank and the oxygen above, form an enormous battery."

"Trimet can soak power from the grid when energy is cheap. It can then resell
the power when demand is at its peak."

My guess: they usually just load shift in response to prices, but when prices
get exceptionally high they resell, and the author mixes the two up.

~~~
dredmorbius
Problem is that there's different information available in different places
which confirm either argument.

The Trimet annual report / brochure linked elsewhere in this discussion makes
clear that this is only demand-side management / load shifting.

The diagram linked elsewhere ... here:
[http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_...](http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_630.jpg)
... shows what could well be a metal-air battery.

It's a fucking disaster of reportage.

------
qwerta
Article is bit misleading. They do not 'store' energy in the same way as
battery, they never pump electricity back to grid. They just adjust their
consumption to use cheap energy.

> By varying the rate at which the metal is produced, the plant will be able
> to adjust the power consumption of the 290-megawatt smelter up and down by
> about 25 percent. Trimet can soak power from the grid when energy is cheap.
> It can then resell the power when demand is at its peak. The company can
> temporarily reduce its power consumption by slowing the electrolysis,
> cutting the energy drain.

~~~
danmaz74
The article isn't clear at all, but they say "It can then resell the power
when demand is at its peak." I wonder if they didn't understand the thing, or
if they missed some very important information about getting energy back from
the aluminium.

EDIT: They also talk about a conversion rate of 90%, so this makes me think
there needs to be a mechanism to generate current.

~~~
qwerta
I think they have contract obligation to take some energy, so they just resell
it.

Anyway the biggest problem of German grid are not really peak hours, but
transporting energy from north where turbines are to industrial south.

~~~
ajuc
I don't know how it works in Germany precisely, but in Poland there's a system
where big energy users can publish "demand reduction offers" and network
operator buys these offers as needed to balance the network.

The basic rule is - those, who unbalances the network pays those that balances
it back for the troubles, so there's huge incentive to predict your power
requirements and transfer requirements precisely. I guess Germany with their
solar cells and wind turbines have a lot of problems with that.

There are a few whole markets set up with energy, transfer capacities,
reduction (or increases) offers by both plants and users, and it works quite
nicely.

I worked on a system for bulk energy trading and it was very intersting to see
how it works behind the scenes.

BTW demand reduction is actually BETTER than storing and returning energy.
Demand reduction of 100 MW frees more than 100 MW (heating loses), and lets
other people use the wires in that time.

~~~
twic
It's similar in the UK - large users can join the "frequency service", where
they respond to demand-induced drops in frequency by disconnecting their
loads, and get a discount for doing so:

[http://en.wikipedia.org/wiki/Control_of_the_National_Grid_%2...](http://en.wikipedia.org/wiki/Control_of_the_National_Grid_%28Great_Britain%29)

Another, unrelated, slightly bonkers UK power supply innovation is the ability
for energy companies to remotely control their customers' supplies using
secret signals embedded in Radio 4:

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

------
tinco
This is nice for soaking up and making good use of peaks, but it does nothing
for the lows, the aluminium can't give back the electricity, so you'd still
need coal plants to complement the wind/solar farms when they're down.

That said, even if we could reduce the need for coal plants that would be a
huge win of course.

~~~
audunw
> but it does nothing for the lows, the aluminium can't give back the
> electricity

Actually, it seems they might be doing precisely that. See the information in
the other comments. It's hard to say for sure, even the primary sources seem
fuzzy. But this graphic seems to indicate that they are indeed extracting
electric energy from the molten aluminum:
[http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_...](http://images.bwbx.io/cms/2014-11-26/tech_aluminumgraphic49_630.jpg)

This presentation also shows the energy arrow pointing from the aluminum plant
to the consumer: [http://www.innovationsforum-energiewende.de/wp-
content/uploa...](http://www.innovationsforum-energiewende.de/wp-
content/uploads/2013/11/Thomas-Flesch-Trimet.pdf)

The most confusing thing about all of this is that they say that they only
adjust their own power consumption by +/\- 25%, which seems to contradict the
statement that they're giving energy back. But as far as I can understand,
this +/-25% is the long term average. Of course they need to consume a
positive net amount of energy during the day to keep the plant running.

But it seems that they are able to pump energy back into the grid for a short
amount of time, which would be during the hours when solar/wind power is at a
minimum.

~~~
graycat
Maybe they are just _giving back_ the energy to the grid in two respects, (1)
energy they contracted for today they do not consume but sell back to the grid
and (2) the energy was to come via the grid to them but, in not consuming that
energy, the energy flows to homes, etc. instead and, thus, at least is
_redirected_ in the grud or, if you will, flows _from_ the aluminum plant _to_
the homes. At one point, they do say _virtual_.

The _losses_ involved are from some somewhat inefficient use of the grid and,
there, losses flowing the energy through the grid.

------
Sanddancer
My first thought when I read the headline was that a German firm had gone
through to find a new substance for use in molten salt storage [1]. Reading
through it, I was a bit disappointed that there doesn't seem to be any sort of
waste heat recovery in place here, which is making me curious. Given that the
molten aluminum needs cooled and shaped into ingots to be distributed to
manufacturers, I'm curious if there is any sort of waste heat recovery system
in place, and/or a system to pump that heat into any sort of a District
Heating [2] sort of system. All that heating in the system has to go
somewhere, and given the sizes of the smelting halls, it seems like it would
be profitable to set some sort of system up.

[1]
[http://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_s...](http://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_salt_technology)

[2]
[http://en.wikipedia.org/wiki/District_heating](http://en.wikipedia.org/wiki/District_heating)

~~~
dredmorbius
The fact that a metal-air battery is a thing, and that aluminum is actually
one of the best anodes for use in them, only confuses the matter further.

[http://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery](http://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery)

------
venomsnake
Here is a billion dollar question: If we mix aluminum with mercury will we be
able to use it as a real battery with high enough efficiency?

Or to get real freaky: thermite -> Fe + Al2O3 + electricity, Then we break
down corundum to al + o?

~~~
dredmorbius
No need to mix it with mercury. An aluminium-air battery is a thing. And among
the best anodes for metal-air batteries is aluminium.

------
graycat
But, could molten aluminum or other metal be used for energy storage?

So, when the sun is shining and/or the wind is blowing, use the resulting
electric power to heat the metal by, say, just simple resistance heating.

Then when want to draw energy from the molten metal, just have some tubes made
of metal with a higher melting temperature carry water to be converted to
steam to turn steam turbines and generate power.

Since I doubt I'm nearly the first to think of such a thing, I have to guess
that the detailed engineering and costing makes it not worthwhile.

~~~
dredmorbius
Yes.

You've got two options. One is the straight thermal route, the other is to run
the aluminum oxidation process forward and backward, in which the aluminium is
the cathode and oxygen from the air the anode. It's just like any other
battery in that you're creating an electric potential difference and current
flow directly.

~~~
graycat
I wondered if it was necessary to boil water

~~~
dredmorbius
It's not necessary, but it's a good route.

You could run a Stirling-cycle engine off a hot and cold end without a phase-
change working fluid. But gas turbines are very efficient (and simple), and
work best when working with the very high-level pressure gradient presented
either by combustion (as with a jet engine) or live steam (with a pressure
drop in the condensed state) as with a steam turbine.

You could substitute other volatile working fluids, but water is cheap,
abundant, and provides useful work at temperatures typically attainable in
systems -- 100 - 1000 C (typically in the 200 C - 500 C range).

