The article doesn't say, but I assume that it's currently in the microvolts.

The harvesting stuff I looked at a few years back for a project were like that. They stored and inverted the voltage for a quick transmission burst, and then went back to harvesting again for the next transmission.

It's microwatts, but it's there.

Well, yes, but you have to start somewhere.

It is useful for other things. You can harvest and store that energy for burst-type sensors that are in remove places. It's what energy harvesting devices do now, save they actually require some other electrical field to work. This could be placed in areas that have no other electrical service.