Hi,
P.S. at the start. This may sound negative towards you and others. I don't mean it that way at all. I'm frustrated with it.
I'm trying to do the same thing, and in a simple way
The 12v zener uses, by definition, 12v. So if something on the other side of it needs 12v to turn on, the supply must be 24. 12vz + 12v(min turn on v) = 24v. A 12v zener and resistor fed 13v, the resistor only has 1v (13-12=1).
We got some almost good results with a 9v zener and a 5v relay (puting power to a 12v relay). Inconsistent operation.
You can get 13.7 or 13.8v zeners if thats somehow the magic number.
My problem has been the second it turns on, the load drops the battery V, which turns it off. The batteryV recovers, and it turns back on. The IC people would call it unstable occillation. They would also recommend a shoe box full of IC's to eaisly fix the problem. I'm sure it will work, but I'm lazy. I'd rather think about it for a year, then build something with 2 or 3 parts. Works for me.
Could you be thinking about it from the wrong perspective? What 'simple load' are you trying to turn on (what plugged into the inverter)? These guys have a lot of experience on running specific things. If its a water heater element, just get a 24v (not 12v because a 24v can handle and use the extra power if its extra windy) element and run it direct. If the genny is only making 1w at 6v, it still gets used, instead of waiting for the wind to get high enough for 12v. Just a simple example, probably not realistic.
Need more info. Post how if you get it to work without us.
G-