The most commonly used solid electrolyte around us is oxygen sensors. For example, oxygen sensor is used in automobile to measure the oxygen concentration in exhaust gas. We must adjust capacity of the air mixed with gasoline in order to make the engine wording better.
The solid electrolyte, which can flow through oxygen ions freely, separates the gas with different oxygen density. In case the solid electrolyte is heated up, the oxygen ions can move from supernal oxygen density to lower oxygen density. And this moving results in voltage- oxygen electric potential.