Bad conversion. You say 100 microjoules is 0.001 watt*hours. But the conversion rate 3.6 billion microjoules to one watt*hour. So 100 microjoules is around 0.0000000277 watt*hours. Or 0.0277 microwatt*hours.
Tiny devices such as contact and temperature sensors or for weather measurement and automation are spreading rapidly. The power supply requires cables or batteries, which a new type of energy cell could change.