How about using the piezoelectric effect to drive an electrical potential difference in a specialized organelle that works like a chloroplast - but runs on the AC power generated through vibrations set up by the storm, and mechanically delivered through cellular structures to piezoelectric crystals incorporated into the cells responsible for energy generation?
Cells incorporate quartz or tourmaline, mechanically situated to deliver vibration from the larger structure that the cell is in, to the material. Networks of wire-like conductors, produced by bacterial colonies which have coevolved with the plant life, and produce conductive plates - natural reference here.
Suppose two variants of the bacteria exist, and they attack one another if they get too close, which prevents short circuits. There would be evolutionary pressure to enforce this, because the bacteria would otherwise kill their host.
Now you have fairly high voltage between two sets of biological, actually conductive wires. These wires bind to opposite ends of a specialized cellular organelle - and implement something akin to whatever the heck these people are doing to utilize electricity directly to generate ATP. Think, a chloroplast that works with the electric potential difference instead of light.
And more standard plant biology follows.