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First clarify where this leakage current will be flowing.  You seem to think that some parts of the solar panel will generate a small current thru the rebar into the ground, but where is the closed loop?

The polarity also matters.  Current flowing one direction from steel to dirty water causes corrosion, but the opposite polarity actually provides some protection.  I don't remember which direction is which.  This is something for you to look up.

Note that galvanized steel exploits this directional phenomenon.  Galvanizing steel means coating it with a thin layer of an anode material, usually zinc.  If there is a break in the zinc coating the zinc and steel form a battery such that the current flows to protect the steel.  This does cause the zinc to be eventually consumed.

Oil platforms in the ocean are usually made of steel, and are protected from corrosion by zinc anodes placed around the structure.  The current from the zinc, steel, and seawater battery protects the steel.  The zinc anodes are slowly consumed by the process, and are periodically replaced.