Bill Gates and gravel batteries...
Something you likely didn't know and wouldn't guess is that Mary Lee and I are environmental wackos. Our home is a Touchstone/Energy Star home with a HERS raing of 52--geothermal with an ERV and all that.
The first two cars we bought were diesel VW Rabbits. The summer of 1979, one pulled a trailer weighing 1,950 pounds from Madison to Boulder. If I'd touched the brakes we would have crashed. Used third gear the whole way at 55 MPH and averaged 37 MPG!
Anyhow, here's a fascinating video...of the latest idea in energy storage now being funded by Bill Gates. (TB)