I have been looking at cheap garden solar lights for power. These things are amazing value. For 3 swedish crowns you get a small solar cell, a 2/3AAA 60mAh battery, an led and a housing. A couple of those should be enough to open and close a valve once a day or so.

For a valve I have discarded all solenoid valves, partly because they use a lot of power and some of them seem to rely on water pressure and water free from particles. And to be honest I dont really understand exactly how they work and what to look for. I have found a motorized ball valve on eBay for approx 120 swedish crowns. I have decided to use this since I understand how it works and there is a big, nice hole for water and particles to go through. The downside is that I will need an H-bridge to open and close the valve and more components mean more money. Did I mention that I am a cheap bastard? :-)

For the brains of the project I will be using a pic microcontroller since they are cheap, can be in low power modes (drawing less current than I can measure) and I frequently use them in my hobby projects. The particulat controller that will be used for this project will be a pic16f886. The reason for this is that it is relatively cheap and I have experimented with low power modes on that mcu earlier and I'd like to reuse the code I wrote.