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Comment by qwerta | Hacker News Reader

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.

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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.

Yeah, the way the article is worded further down strongly suggests that they are using the aluminium as an energy source:

"Using the production process as a virtual battery is “an interesting option” for the industry, said Marian Klobasa, who heads the demand response and smart grids unit at Germany’s Fraunhofer Institute for System and Innovation Research ISI, an applied science researcher. If the volatility of the power market increases, Klobasa said by phone from Karlsruhe, “then it may make commercial sense and be economically worthwhile.”

Trimet’s Hauck estimates the full costs 70 euros to 150 euros to store one megawatt-hour based on 1,000 hours of use per year. That would make supply competitive at some periods of peak demand during the winter."

Aluminium plants in the UK already do demand shedding at time of peak load on the UK power grid - I'm sure German plants do much the same thing.

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.

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.

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...

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

Thanks, this clarifies what they actually meant.

Is it possible they could be able to use their pools as an electrolytic capacitor?

They are melting aluminum oxide, which is used as the insulator in electrolytic capacitors, and the extracted aluminum pools at the bottom apparently.

If they are able to maintain the oxide layer at suitable thickness, do they not basically have a capacitor?

Hmm, theres at least this quote:

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

I know nothing about battery chemistry, does that make any sense?

Yes. It's the same tech they use in things like hearing aid batteries [1]. The metal oxidizes, which can be harnessed to create an electrical current.

[1] http://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery

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