Controlling 32 solenoid valves from a single BeagleBone Black
There are many ways to control higher-powered/higher-voltage devices with MCU GPIO pins.  Your suggestion to use SSRs could work but these are somewhat expensive and not really needed here.
The most common way of driving loads such as your solenoids is via a simple circuit such as this:



simulate this circuit &ndash; Schematic created using CircuitLab
Pick appropriate values of the R and NPN transistor so that you can optimally drive the relay coil.