The innovation here isn't the generation of ridiculously small micro-currents from raindrops (we've seen that before) but the use of expensive carbon fiber materials (that don't rust) to do it.

> In experiments, a single 92-microliter raindrop generated up to 60 volts and several microamperes of current. When four generators were connected in series, 144 LED bulbs lit up instantaneously.

"Instantaneously" in this instance meaning "for a fraction of a second" -- specifically, the time between the drop hitting and it bouncing/reforming into a bead. Probably (back of the envelope) for on the order of 0.1 seconds.