Keep them in a cool, dry, very dark spot. Potatoes go green when exposed to light. It’s not only sunlight that is harmful ..... all lighting does the same thing. The green is not only on the skin. The flesh inside also gets discoloured. Although only poisonous when consumed in large amounts, the potatoes won’t taste good. If you want to keep them for an extended period of time then store them in the fridge to stop them sprouting, as warmth is their trigger to shoot. Between 4 and 15 degC is ideal for lengthy storage.