How to use anodic and cathodic overpotentials to calculate electrolytic energy efficiency?

I am trying to calculate the energy efficiency for $$\ce{CO2}$$ reduction to formate, coupled to water oxidation based on literature data.

$$\ce{CO2 + 2e- + 2H+ -> HCOOH}$$ $$\ce{H2O -> 2H+ + 1/2O2 + 2e-}$$

I hope someone can help me to understand how to combine the information that is presented in the papers so I can calculate an overall energy efficiency of the reaction.

E.g. things that are given:

• cathodic overpotential
• anodic overpotential

The energy efficiency should eventually be equivalent to $$\mathrm{EE = \frac{Combustion\;energy\;of\;Formate}{Invested\;electrical\;energy}}$$