Off-grid Solar with DC Backup
I'm not positive from your question, but I think you might be over-engineering a typical solar setup.  All you have to do is connect the solar panels through your charge controller to the batteries.  Then run your DC equipment straight off the batteries.  The DC equipment will draw from the batteries as priority, but as soon as they start to drop in voltage, the charge controller will kick on and allow the solar panels to charge them -- which means that you will effectively be pulling the net power from the solar panels so long as their is power available from them.

The only reason you might try to skip the batteries is if you wanted to minimize the load you put on them, but honestly, you should just get a good quality desulfator to put on your batteries and then you'll never have a problem with keeping them in the equation.

As a side note, what a lot of people don't realize is that your solar panels could supply 36 volts to charge the batteries and the batteries will automatically act as a "soak" for the power, which results in 24 volts (if that's what your bank is rated at) available to any appliances you connect.  Some engineers argue with this because its not mathematical enough for their minds, but in practice, it works perfectly.  Real practice > the model.

To further back my point, most commercial setups will claim you need diodes in your system to prevent reverse current leaking back through your panels when they aren't doing anything.  Try measuring the reverse leak current and you will laugh your butt off.  It's tiny.  The diodes are overkill in a lot of systems.  Keep it simple.