Essentially when you combine charging
systems they work "in parallel" -- whichever has the highest voltage output in its configuration for a given "stage" puts the most power on the bus. With wind
its a little tricky because you have to burn the power off or the unit can overspeed. With solar its not that much of a big deal - disconnected or free-floating solar panels
So the way that most people wire things up is as follows:
Solar -> MPPT
charge tracking converter/charger -> Positive and Negative charging
posts on the batteries
-> directly to the same posts.
Wind -> controller with diversion load -> charging posts
-> Some multi-stage charge controller -> charging posts
Then you try to configure them as close as possible to the same config and let 'em sort it out. Yes, its safe as none will really "backfeed" the other - they all sense the voltage at the charge point, and if its above their set threshold for the state of charge (bulk, acceptance, float) they are in, they throttle themselves back and don't contribute because contributing would require them to force additional current
through the system, and that would by definition raise the voltage further. (V = IR, after all, in a typical mostly-resistive, mostly-linear, mostly-DC system).
Now, the trick is matching the wind and solar up, as many wind units don't have multi-stage charge controllers. Blue Sky has a charge controller with MPPT
AND a diversion load, which can manage the wind input simultaneously with the solar input, and doesn't care if the solar or wind are set up for 24V and the battery
output is 12V (or v-v, I think). Its the 3024iL and there is a diversion option for it. This is the controller I've decided to buy for myself (no affiliation whatsoever with the company, I'm just doing the same research
as you right now). This would then combine the wind and solar charge points into a single
unit and has the advantage of being able to dump current
to something such as a water
heater element in good wind/sun days to give you some (probably tepid) hot water
. Alternatively you can wire the HW heater to AC, and just dump the excess energy through a dump resistor or find some other creative use for it.