A few days ago, I was at a park near Paine Field (Everett) - and there was what I'm reasonably sure was an electric airplane doing circuits. It was basically shaped like a sailplane (long, thin high aspect ratio wings) but was nearly silent - no motor noise, just a drone like whirring noise from the prop.
I know there is at least one aircraft company working on battery powered aircraft headquartered at Paine Field - I wonder if was watching a test...