Here is a WiFi based solar powered camera, for closer to home.
Here is what I think you are looking for, which will do wifi or 4G (they mention you need to specify the country you are in to make sure they send you a unit that works)
With either one, with WIFI enabled you should be able to set up some decent antennas at each end and get the target range you need as long as you have direct line of sight, but the second type seems more to be what your boss is asking for, what with 4G capability. Good luck.
Ebay search for solar camera 4g
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