The 24V part means that is what it takes to turn them on. Hence your swithces are hooked up to 24V there for it will turn them on. However, if you have low batteries, a bad battery or just using the shit out of them then u will have a drop in voltage and the solenoids wont work properly. That is why it is better to use 12V solenoids so if there is a drop in volts then they should still work properly.
This is the way Pat Burke explained it to me about 2 years ago so if I am wrong please correct me.