booysenc

Hi, which sonoff do you have? if you are comfortable with some hardware modifications I'll assist where you make some changes on the PCB so the output of the sonoff is not a live connection but you can use it as a dry contact (regardless the warranty will be void), sonoff has some 4ch modules that offer dry contacts out but reckon it's a bit of an overkill, unless you want to wire up additional things like lights etc.
once that is done, you can set the device to itching and give the gate a short trigger to the controller and open the gate. I personally don't like this because if there's a glitch on the sonoff my gates might open and currently there's no way to view that feedback remotely.
Another feature I asked for waaaaay back when is if there's any way to use a sonoff to show the status of an external device, like a gate, if the external signal comes in the sonoff shows on/off whatever, just some feedback

Actually now that I think of it, probably just a mini that's powered by the inverter supply and a relay that's held in by eskom supply, when it drops out you trigger the switch input on the mini, when it switches on again you toggle the switch input on the mini. Ai was hopeful our request could be heard... 

Yeah!! A topic that was discussed with sonoff a few times that will help with loadshedding is the ability to trigger if something goes offline or stays offline for say 5min or a selectable time(to prevent connectivity triggers) . This can already be done if another device switches on or off. I can then dedicate a sonoff for loadshedding monitoring