Abstract The present article deals with the working principles of regenerative wet photovoltaic cells compared to n-p-type junction dry photovoltaic cells and photo-electrochemical cathodic protection short-circuited cells from thermodynamic and electrokinetic aspects with a pedagogical motivation. Additionally, it introduces two hypothetical regenerative hydrogen/oxygen photovoltaic cells conceptually designed for the first time to our knowledge. Their working mechanisms are discussed in terms of the single shifts of the redox Fermi level to the flat band Fermi level, $$\left({E}_{\text{F},\text{ fb}}^{\text{n}}-{E}_{\text{F}}^{\text{redox}}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mrow> <mml:mtext>F</mml:mtext> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mtext>fb</mml:mtext> </mml:mrow> <mml:mtext>n</mml:mtext> </mml:msubsup> <mml:mo>-</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mrow> <mml:mtext>F</mml:mtext> </mml:mrow> <mml:mtext>redox</mml:mtext> </mml:msubsup> </mml:mfenced> </mml:math> , in the negative potential direction and $$\left({E}_{\text{F},\text{ fb}}^{\text{p}}-{E}_{\text{F}}^{\text{redox}}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mrow> <mml:mtext>F</mml:mtext> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mtext>fb</mml:mtext> </mml:mrow> <mml:mtext>p</mml:mtext> </mml:msubsup> <mml:mo>-</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mrow> <mml:mtext>F</mml:mtext> </mml:mrow> <mml:mtext>redox</mml:mtext> </mml:msubsup> </mml:mfenced> </mml:math> in the positive potential direction during illumination. These negative and positive single shifts are directly responsible for the generation of photo emf (electromotive force) and occurrence of both the negative inverse overvoltage, $${\eta }_{\text{h}}^{\text{n},\text{ l}}<0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>η</mml:mi> <mml:mrow> <mml:mtext>h</mml:mtext> </mml:mrow> <mml:mrow> <mml:mtext>n</mml:mtext> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mtext>l</mml:mtext> </mml:mrow> </mml:msubsup> <mml:mo><</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> , for photosensitized anodic oxidation by the valence band (VB) minority holes in the n-type anode and the positive inverse overvoltage, $${\eta }_{\text{e}}^{\text{p},\text{ l}}>0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>η</mml:mi> <mml:mrow> <mml:mtext>e</mml:mtext> </mml:mrow> <mml:mrow> <mml:mtext>p</mml:mtext> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mtext>l</mml:mtext> </mml:mrow> </mml:msubsup> <mml:mo>></mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> , for photosensitized cathodic reduction by the conduction band (CB) minority electrons in the p-type cathode, respectively, on the energy band diagram as well as the photocurrent I vs voltage V polarization curve. The splitting of one unique equilibrium Fermi level $${E}_{\text{F}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mtext>F</mml:mtext> </mml:msub> </mml:math> , at which chemical potentials of majority and minority carriers overlap in the dark, has been detailed between the two quasi-Fermi levels of majority and minority carriers, $$\left({nE}_{\text{F}}-{pE}_{\text{F}}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msub> <mml:mrow> <mml:mi>nE</mml:mi> </mml:mrow> <mml:mtext>F</mml:mtext> </mml:msub> <mml:mo>-</mml:mo> <mml:msub> <mml:mrow> <mml:mi>pE</mml:mi> </mml:mrow> <mml:mtext>F</mml:mtext> </mml:msub> </mml:mfenced> </mml:math> , which is a measure of the departure from thermodynamic equilibrium ( $$\left({nE}_{\text{F}}={pE}_{\text{F}}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msub> <mml:mrow> <mml:mi>nE</mml:mi> </mml:mrow> <mml:mtext>F</mml:mtext> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mrow> <mml:mi>pE</mml:mi> </mml:mrow> <mml:mtext>F</mml:mtext> </mml:msub> </mml:mfenced> </mml:math> at equilibrium), where the mass action law no longer applies. Both single shifts of the Fermi level during illumination are confirmed to be almost equal in value regarding the difference between the two quasi-Fermi levels, $$\left({nE}_{\text{F}}-{pE}_{\text{F}}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"