I reported last week that Germany, leading the world in switching to a renewable economy, is getting swamped by a deluge of new energy, owing to the success of its Feed In Tariff policy.
What to do with this rather interesting problem? Repurposing old coal mines to store that excess juice is one solution.
From Cleantechnica:
In an interesting marriage of clean and dirty tech, Deutsche Welle is reporting that the state government of Lower Saxony in Germany is looking into repurposing old abandoned coal mines inside the Harz mountains as pumped storage for wind power.
The idea has attracted approval not only from environmentalists in the region, who like the invisibility of the storage, but also from former coal miners, who like the idea of the disused coal mines being put to good use as a kind of “green battery” for wind power.
“The tradition of mining is so great in the Harz region, that they want to see the mines back in use again, so there are practically no critics of the project,” noted Marko Schmidt, an engineer for Lower Saxony’s Energy Research Center, who came up with the concept.
This acceptance is surprising to someone who has lived for so long in America, where green energy has to do battle, for different reasons, with both sides. Perhaps this pragmatic approach (when coupled with its uncomplicated embrace of green energy) is responsible for Germany’s economic growth.
Variations on ideas for pumped storage are surfacing now that the world needs to integrate intermittent wind power with the grid, but Schmidt’s innovative idea would be the world’s first use of an abandoned coal mine for this purpose.
Traditional pumped storage uses gravity to harness wind power. Water is pumped up a hill to a reservoir by wind power when it is available, typically at night, so that it can be released downhill when it is needed, using gravity to drive the turbines to make electricity.
In this case, the pumped water would be stored inside the mountaintop, rather than on it, in a reservoir, but it would still be high enough so that gravity could be used at the bottom to drive turbines when it is released. This would be a contained loop system, so the water does not contaminate rivers at the bottom.
Schmidt estimates that a pilot plant could be built in Bad Grund within the next three to five years for between 170 and 200 million euros, that would be large enough to provide up to 400 MW of storage capacity at a time, enough to power 40,000 households for a day.
Each typical windy night could be “time shifted” to power the following day’s daytime needs in this way, one day at a time. Schmidt also believes that there are up to 100 other sites in Germany that could be similarly utilized, simply by adapting the no longer used infrastructure of the fossil age.
Source: Clean Technica (http://s.tt/12GXc)
How much height differential can they get with coal mines in mountains? That height differential is crucial the efficiency and economics of the system. I did some research on this, and it’s obvious from the site that they are proposing to use a height differential within the mine. In other words, the high storage will be the upper levels of the mine, and the low storage will be in the lower levels of the mine. I couldn’t find any of the technical information on the mine, so I’m left to wonder about a number of possible problems. The most important of these are 1) how much height differential can they get? and 2) how much water can they store in one reservoir? Pumped storage requires a LOT of water: the Taum Sauk pump storage reservoir, for example, has 5 million cubic meters of storage. If we model (quite simplistically) a mine as a set of shafts roughly 3 meters high by 3 meters wide, then we’d need 500 km of such shafts to get that much storage — at BOTH upper and lower levels.
I also wonder about water leakage and filtration. If they just use the existing galleries without any lining, they could easily lose a lot of water, especially if the water pressure opens up new channels. I would also expect the water to get a lot of sediment mixed into it, at least in the first year.
Anyway, this is certainly a fascinating idea, but I myself see no problem with conventional open-air pumped storage. What’s so objectionable about a reservoir?
some people don’t like the visual impact of a reservoir, and in a crowded country like Germany, space is at a premium, so using existing sites makes sense. Here in Michigan, we have a pumped storage facility on Lake Michigan, and we’re glad to have it, but probably won’t build more, because the dune habitat is so precious. More likely we will use existing space from abandoned salt mines and other caverns that are abundantly available due to local geology – with some already in use for natural gas storage – to create compressed air storage facilities, as are currently being planned in other parts of the country.
For the love of Newton. Is you are going to write about energy, cleantechnica, learn the difference between energy and power.
“400MW of storage capacity”
It’s really important.
*if, obviously
I can understand why people get so readily confused about the figure of merit for pumped storage facilities, because it really is a combination of both total energy content and maximum power output. The more important figure is the maximum power output, because that indicates the size of the peaking power plant that is obviated by the pumped storage facility. However, if the generators are sized improperly relative to the total energy storage, the maximum power output is meaningless, because the storage could be exhausted in a time too short to be useful.
Fortunately, it’s safe to assume that the designers aren’t idiots, and so have sized the facility to provided several hours of peak power. For this reason, the maximum power rating is the most useful figure of merit. And its dimension is a little too tricky for most people to understand:
“400 MW of peak power capacity”