To be clear, the potato is not, in and of itself, an energy source. What the potato does is simply help conduct electricity by acting as what’s called a salt-bridge between the the two metals, allowing the electron current to move freely across the wire to create electricity. Numerous fruits rich in electrolytes like bananas and strawberries can also form this chemical reaction. They're basically nature’s version of battery acid.
"Potatoes were chosen because of their availability all over including the tropics and sub-tropics," Rabinowitch told the Science and Development Network. They are the world's fourth most abundant food crop."
But besides being rich in phosphoric acid, spuds are ideal in that they're composed of sturdy starch tissue, can be stored for months and won’t attract insects the way, say strawberries, would. Additionally, boiling the potato breaks down the resistance inherent in the dense flesh so that electrons can flow more freely, which significantly bumps up the overall electrical output. Cutting the potato up into four or five pieces, they researchers found, made it even more efficient.