the voltage output and resistance of a potato
The open cell voltage, Voc for the boiled potato with Zn/Cu plates is 760mV due to Reduction 


Zn+ 2H+ → Zn++ +  H2  


Extra Info

For any battery curve with a voltage, V vs current, I you can compute ;
- the slope or Effective Series Resistance, ΔV/ΔI=ESR[Ω]
- maximum power transfer (MPT) for pulse load (~50% Voc) for load ~ ESR
- maximum mWh or mAh vs load R usually for load >>ESR    

Here the author plotted R load [kΩ] vs the inverse of current [1/mA]

In terms of energy cost mWh/$ which is more convenient than J/$, this can be extracted from the same curve of μWh/cm² vs mVolt by computing the ESR of the boiled potato. From P=V²/R estimate data values from plot into a spreadsheet.


Then consider what is the optimum load from R=V²/P using the  plots [mV²]/ [μWh/cm²] 


Using a spreadsheet I am sure you can work out the optimal load R for a given area and thickness of boiled spuds and make arrays to match the desired load for V=IR= Voc-I*ESR.





This may be good for 3rd world tropical countries that can grow potatoes cheaply AND it's bio-friendly.