A thermopile or powerpile generates:

A thermopile or powerpile generates hundreds of millivolts due to its design, which consists of multiple thermocouples connected in series. This configuration allows it to convert heat energy into electrical energy efficiently. When a temperature difference is applied across the junctions of the thermocouples, each junction produces a small voltage. By connecting several of these junctions together, the total voltage output is significantly increased, often reaching ranges in the hundreds of millivolts.

This high output is essential for various applications where a reliable power source is needed, such as in gas appliances for ignition systems. This ability to generate a substantial voltage makes thermopiles ideal for powering devices that require a stable energy supply without needing external power sources.