It's not useless. There are not that few IOT style applications where one could extract significant energy from e.g. atmospheric temperature cycling during the

It's not useless. There are not that few IOT style applications where one could extract significant energy from e.g. atmospheric temperature cycling during the day relative to a thermal mass. This would not require sunshine, only that the temperature over the day changes about 10K between minimum and maximum. Or with a large enough thermal mass it could use this cycling over multiple days, which might be more reliable. It also has the great benefit of not requiring something fragile exposed to the sun. This makes the feasible reliability potentially much higher, depending on how good this thermoelectric generator lives.