Check out http://jrse.aip.org/jrsebh/v2/i3/p033103_s1 for the abstract. They say its cheaper than a AA battery and can be used to power a low-power LED light. I have not dug into the numbers to see if the cost claims are right. It would seem that with the low power that one gets from each cell you will need a lot of potatoes; the authors say they need 5.
My dad is visiting us from India and is sitting across from me. He tells me that 5 potatoes in India costs Rupees 15 (~30 cents). He tells me that a AA battery is either a bit cheaper or comparable! And I still need to buy some zinc and copper (and a pot to boil the potatoes, and spend some money heating it)
I get the impression that this is sort of a cute press release of something we already know and I wonder if it solves anything. I have to boil the potato and so need energy; I gain a means of making electricity, but I lose food to do that. And we really need someone from countries in the developing world to tell us if the cost numbers are what my dad tells me they are in India.
Anyway... could not resist.