I am not familiar with batteries used in solar power systems, but I believe 12VDC output is pretty standard and OpenSprinkler DC-powered or Latch both accept 12VDC input (a few volts higher is fine, but should not be more than 15VDC).
Latch is supposed to be more power efficient as the valve stays indefinitely in one state and only draws power when you change its state (from open to close and vice versa). That said, the controller itself also consumes a certain amount of power (around 100mA to 150mA in idle state). As it uses linear regulator to drop 12VDC to internal voltage, this is a power consumption of about 12*0.1 to 12*0.15, which is 1.2 to 1.8 Watt power, which pretty small.
If you go with DC-powered OpenSprinkler, each valve when open consumes about 12VDC * 0.3A = 3.6 Watt power.