This doesn't seem right. Anyone who has been in a cattle barn knows the kind of heat that cows give off. The energy demand for the sensors should be very small.

This doesn't seem right. Anyone who has been in a cattle barn knows the kind of heat that cows give off. The energy demand for the sensors should be very small. 20% efficiency for the solar cells might be true on paper, but not in practice - diet, orientation, even needing 4x the solar cells because you cant guarantee the cells will always face up (collar rotates).