I was reading the wiki article on Piezoelectricity and this effect is either really odd or I'm missing something obvious here (I know wikipedia is not the best source but I'm feeling lazy). The article states that a Piezoelectric material will produce a voltage in response to mechanical stress. So looking at the picture there it looks like simply applying pressure to something will produce a voltage that I can run an electric load on. If that is true then we can just put one of these under a mountain and humanity's energy needs are taken care of forever!? Something about that just doesn't make sense. Do they mean that the increase in pressure produces a voltage but after that pressure is done increasing the voltage drops again? So dropping a mountain on one of these would make a lot of energy obviously lol.