I've had a former student return with a question that I could use some help with...
In his community, a developer wants to convert an old quarry that is now a man-made lake into a power generation scheme. The developer would excavate under the quarry. Then, during the day, they'd let the water run from the "lake" down into the holding tanks underneath, in the process turning a generator and creating electricity. Then, at night they'd pump the water back up to the "lake" when the electricity was cheaper. In this way they'd generate electricity and the claim is that this is "green" electricity.
The student came to me because he remembered (yes, I did jump for joy that someone remembered something I had presented them as part of the class!) that no process could have an efficiency of 1, so his thought was that this process is not "green" as advertised. He thought that due to this loss, this process would ultimately consume more electricity than it would generate and that it was just a "shell game" for making money.
Well, my first inclination is to agree with him. However, I did tell him that he was trying to apply an efficiency concept from Thermodynamics to electricity generation. I assured him I'd do a bit of digging and get back to him. Well, I can't seem to find how I might calculate the efficiency for this process and how to determine if it is truly "green" or not -- thus being a way to make money but not be green.
Any suggestions and/or help would be appreciated,
Peter