I know this has been discussed a little already, but I am coming at this from a farming perspective, not a gardening one. We have a 25 acre organic vegetable farm, and we have about 5 acres per year on drip irrigation. The water is supplied through a 2" mainline, then to 1.5" drip header, which supplies 1/2" drip tape. Drip can only handle limited pressure (12 psi), so there are multiple zones and each one has a pressure reducing valve between the mainline and the drip header.
What would be extremely useful is a remote controlled valve for the drip header. It could be after the pressure reducer, but it should not interfere with flow, which a 3/4 inch solenoid might. But I think 24v and 2amps should be enough. The onboard power could not do it.
I imagine a box with a 12v ATV battery, a voltage doubler, the pinnocio, and a small solar panel, and some relays. This would wire to the solenoid, which would turn on the irrigation when needed.
I could also provide weather station functionality if so desired. There's lots of other areas this would be very useful, like in the greenhouse, cold room monitoring. 24v is adequate to do all sorts of stuff on the farm, including rolling up greenhouse curtains, opening louvres, turning on and off electric fencing, etc. . .
I just don't know how to wire it or make it. I'm not sure how big a solar panel would be required, and I don't know how to program pinnocio, yet. Anyone willing to help out, please let me know!