An alternative solution appears to be to get a Zigbee Fingerbot with “ToolPack”, attach the Fingerbot to a rocker switch, and connect the rocker switch inline with the solar DC power cord, all in a waterproof project box.
There are a good number of Zigbee relays out there, but they all assume a steady power supply and are not designed for battery operation.
This is the same issue as a battery powered light: listening constantly for the next “on“ command for the network tends to use too much battery life, so you just aren’t likely to find these.
Battery powered devices are usually ones which initiate a network message, like sensors, and can control how often they report in, thus extending battery life.
Anything where the messages are more typically coming from the hub to the end device have to be continually listening for that message, so they just aren’t as likely to be battery powered.
This was discussed In detail about a year ago, and nothing has really changed since then:
The exception is obviously locks, but that’s a whole separate discussion, and as you probably know, they tend to use at least four AA batteries. So the larger size of a lock makes this more practical. This is also covered in detail in the thread linked above.