This is the newer version of NO - Normally Open DC Control SSR. It has a Constant current source that is more stable and robust.
DC-AC Solid State Relay or SSR - del30008
You could use it to control AC powered Electricals like Heaters, Motors and Fans. It can also be used to Switch ON and OFF any Equipment, Control Panel or System.
You have to choose the correct current rating and heatsink needs of Triac. This is the older version below. It has a shunt current control. This new circuit above has a regulated current source.
This is a basic output Module in control systems. It is faster than Electromagnetic relays but has some heating in the triac. Some designs with mosfets are also available. SSR with a IGBT - Insulated Gate Bipolar Transistors also can be made for large powers.