The figures you supplied suggested the impedance of the solar panel is 5R and the current difference when a diode is replaced by a Schottkey diode, will be 8%.
But a solar panel does not work as you have suggested. When a normal power diode is replaced by a schottkey diode, the voltage across the load decreases by about 0.3v and this will cause a higher current to flow. The solar panel will not be able to deliver this current and consequently the voltage produced by the solar panel will also reduce and the current will remain almost exactly the same as before.
In other words, as I said, it does not mater if you use a power diode or Schottkey diode as the "reverse current" protection.