What is the ampere of a piezo material
Piceramic recommends the E821 module for collecting energy with your piezo patch.

The datasheet for the E821 says it provides pulses of 100 millwatts that are 80 milliseconds long.  It has to save up energy over time to get enough energy for each pulse.

Assuming you need 3.3V, then 100 milliwatts means you get 30 milliamperes of current for 80 milliseconds from the converter module.  How often you get those pulses depends on how much your patch is flexed.

That ought to let you know if you can do anything useful with your piezo patch.