430-Meter-deep lake supplies electricity

The invention is considered the fourth pillar of the energy revolution. The principle seems ingenious: a kind of piston is moved up and down in a house – similar to an engine – displacing water that flows through a turbine and generates electricity. If solar energy is used to power the piston, the result will be something like a "perpetuum mobile."
This system was invented by wunsiedel professor matthias popp, who teaches energy technology at the georg simon ohm technical university in nurnberg. 13 students at the technical university of nurnberg pondered how coarse the patented invention had to be to be able to supply a city the size of forchheim completely with energy. They presented their results at an "energy conference" at the forchheim public utility company. Students of the faculty of mechanical and process engineering worked out a study on how an entire area can be supplied with regenerative energies. The focus was on the stulpmembrane storage system, which according to professor popp is a key component for the energy turnaround.

Enormous dimensions

Given the energy requirements of the city of forchheim, the dimensions of such a plant were enormous. A 430-meter-deep hole had to be dug and concreted for the 130-meter-diameter storage tank. In the middle of this water-filled basin, a piston, which is first cut free and then enclosed, is raised and lowered. "Motor pumps, like those used in pumped storage power plants, lift the piston. When the piston is lowered again, it displaces the water beneath it. The resulting current drives a turbine that generates energy", explains professor popp.
To ensure frictionless movement, the piston must be sealed with an obturator diaphragm. The students calculated that a storage facility of the size described could generate roughly 26 megawatts of electricity, more than half the annual consumption of the forchheim population, including the businesses located here.
The reservoir presented in the study had a capacity of 6.5 million cubic meters of water, which corresponds to the average water consumption of all households in nurnberg in half a year. At the lowest point of the crater, the water had a temperature of 95 degrees celsius. Which means that the environment of the store would heat up over time.

Innovation is crucial

"This loss of energy will not affect the kilowatt-hours generated, because they were generated by hydroelectric power", explains reinhold postler, technical director of forchheim's public utility company. Moreover, at some point – the students calculated a period of about 50 years – the environment would be saturated with warmth, so that the heat loss could be reduced from an initial 60 percent to about 20 percent.
Dreams of the future? "I could already imagine that at least a model project of such a stulpmembrane storage tank would be built", states reinhold postler. However, high demand funds were necessary. After all, the students estimated the financial requirements for this project at 200 million euros. Apart from whether such a plant will be realized, postler wants to further intensify the cooperation with the students of the technical university of nurnberg. He is convinced: "your projects serve to advance social developments."

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