Yeah, solar for charging batteries to then run solenoids, absolutely feasible - but most solenoids are either Normally Open or Normally Closed, and need constant power when holding them in the other position. For relatively low-flow situations these are non-starters, as you usually want to have a circuit open for an hour or more.
There are switching solenoids that only draw power as you change state. Downside, they don't fail safe. They're also more expensive, and AFAICT you can't use standard (NC / NO) controllers with them. To complicate matters, switching solenoids usually want a certain amount of pressure (about twice what I'm working with).
It's an area that's slowly getting better served by cheap fab places out of China. You can already get A$20 'residential' grade 13mm single line water controllers that are mostly reliable, but their valve comes down to about a 1mm hole, so big impact on flow rate, and highly susceptible to debris.
There are switching solenoids that only draw power as you change state. Downside, they don't fail safe. They're also more expensive, and AFAICT you can't use standard (NC / NO) controllers with them. To complicate matters, switching solenoids usually want a certain amount of pressure (about twice what I'm working with).
It's an area that's slowly getting better served by cheap fab places out of China. You can already get A$20 'residential' grade 13mm single line water controllers that are mostly reliable, but their valve comes down to about a 1mm hole, so big impact on flow rate, and highly susceptible to debris.