I want to use the pi to analyze the moisture of my plants and decide to water or not. I want it set up in the garden. There is no power supply, so the pi will need to run on batteries.
The plan is that the Pi starts every hour, takes measurements, decide if watering is needed and sends logs to my home server via WiFi.
a) How much sense does it make to just have the Pi on all the time, but idle, and then wake up and sleep later?
b) Does it make sense to, alternatively, create secondary circuity with a timer that turns the pi on/off? How complex would it be? Would this approach save lots of energy?
c) What duration can I expect for the batteries under these circumstances?
d) What about adding a solar cell to reload the batteries? I already have some solar lamps around that grab sunlight and power small leds at night.
EDIT: A friend of mine proposed to have the battery + solar cell and something like this: https://de.hama.com/bilder/00121/abb/00121949abb.jpg. The idea is to hack the remote control and let the server-pi controls it. Then, use the outlet as a switch between the battery and the pi. Every hour the server-pi starts the outlet for 5 minutes. What about this ? Definitely cheaper than arduino+Wifi