A day like every other in the XIX century, Michael Faraday noted how an electrical conductor near a magnetic field was generating voltage. He discovered one of the most transcendental methods to produce electricity.
It was 1831, the first working and portable electricity generator. After it, others thought similar mechanisms like turning a magnet with a crank. As easy as that, a little device attached to a bike produces enough electricity for turning on a light-bulb.
Those pioneer dynamos had a little issue because they didn't generate energy most of the time, only when the poles of the magnet passed near the conductor with the well-known effect called electromagnetic induction. The next state of the art was to wire the conductor through a circumference, therefore the magnet could induce more current. This model was used industrially.
Producing electricity frequently involves two simple elements like a magnet and a conductor, or also a piezoelectric element and a shock; even a lemon and a piece of conductor. Semiconductors and Sun are another clear suggestion to produce voltage. All these elements were there for million years and for that, with this knowledge anyone could surprise our ancestors taking a time machine!