There isn't much useful "work" one can do with a microwatt at "human" scale in a day. Except, as this paper shows, build a networkable wireless system camping on those microwatts.
Not meaning to be critical, rather just want to clarify that our modern-day gigawatt-scale energy grid yields an enormous 15 orders of magnitude more electrical power than the microwatt-scale "harvesting" of TV signals can. That's an enormous power spectrum, shown to have a newly useful application (batteryless mesh networking) at microwatt scale.
Not meaning to be critical, rather just want to clarify that our modern-day gigawatt-scale energy grid yields an enormous 15 orders of magnitude more electrical power than the microwatt-scale "harvesting" of TV signals can. That's an enormous power spectrum, shown to have a newly useful application (batteryless mesh networking) at microwatt scale.