ES2: “batteries not included.” - How little is enough for real energy autonomy?

Much has been said about energy scavenging and much has also been said about low power circuitry**. It's a bit analogous to Woody Allen's movie Annie Hall *. But the go al of energy autonomy depends on both sides of the equation. The aim of this evening session is to present the theoretical and practical issues from both sides, add in some system-level techniques, and then follow up with debate on the issues relating to getting realistic energy autonomy. How much do you have to generate? How much are you allowed to consume? Can anyone agree?