EDIT: They also talk about a conversion rate of 90%, so this makes me think there needs to be a mechanism to generate current.
Anyway the biggest problem of German grid are not really peak hours, but transporting energy from north where turbines are to industrial south.
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.
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:
"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.
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?
"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?