Its interesting they have gone with Solar panels. Most post boxes are built over the top of power cables that run under the street likely right next to them but

Its interesting they have gone with Solar panels. Most post boxes are built over the top of power cables that run under the street likely right next to them but its a testiment to the cost and difficulty of getting them connected that solar cells integrated into the top of the box is cheaper and easier. Looks to me like they are using ~43 cells of the 60mm x 90mm variety. They are about 0.6W peak so about 26W of peak output but its never at the right angle. You get about 1000 hours of that in the UK over a year with a good angle, so about 26Kwh a year of energy but I suspect they get half that. At typical UK rates that is about £3.5 a year. Its certainly enough to run a raspberry pi zero and something else, on average they have about 1.5W but during the winter it only be about 0.3W available, which a zero can do at idle so long as the scanner doesn't add much on average. If they have done a completely custom embedded system then potentially pressing that button wakes and powers the device for a period of time or until its finished the scan, connected to 4G and then sent the details, which would save a tonne of power and allow them to do a lot of parcels off a modest battery. Interesting engineering problem where going deeper with more custom hardware and software pays off a lot in reduced power consumption and a basic raspberry pi zero is going to waste a lot of energy and be marginal in the winter.