It's a pretty cool concept hey.
My current feeling on this is that all energy is free and the only questions which need to be asked are as follows:
1 - How much energy has been used to create the device?
2 - How much energy can the device produce during its lifetime?
3 - If the answer to 1 is less than 2, the device is useful.
It was this subject which led me to electroculture for the last few months. And I must say, am very excited to see the results this summer!
All the best to you :)