I've put together a very small series of voltaic piles to produce about 5 volts in order to run a small LED light. Through experimenting i found that the voltage does not vary much no matter the volume of electrolyte ... so why not go small.

I've used the tips of drinking straws, heat sealed at one end, to hold a small piece of tissue soaked in vinegar and water solution into which is placed a small anode made of copper and a cathode made of zinc (small nails). The potential difference created by one cell is around 0.95 Volts here in South New Zealand in winter on a dry sunny day.

 

Connecting the cells in serial series increases the voltage so i will continue to add more cells to eventually run a multiple LED torch. If it works out it could be well worth carrying a bunch of copper and zinc nails (very small) when i go bush to create a small light. I expect the cells will reach equilibrium quite fast by saturating the small tissue with resultant compounds that will increase resistance to a point where voltage is negligible. That is if the solution does not dry up first! Either way i will create a series of about 30 cells and update this page with how long it runs for.