How to calculate power output in piezoelectric material?

Hi,

I want to use piezoelectric material to harvest compression energy, i need to calculate the power output but i can't find enough information on the web to figure it out...

First, I want to learn how to calculate the power output of piezoelectric material using d33 and g33 data.

Second, what kind of piezoelectric material should i buy to get the most power at low frequency under a stress of 0,5 kN for the price.

Third, how piezo cable perform vs ceramics, because it would be a lot easier to install them in my device.

Thank you all for your responses!