I have at times had engineering students come by with requests for ways to measure various kinds of electric fields. I know the earth has an electric field of the order of 100 Volts/meter, but how do you measure it?

Here is a cute way to measure such fields. It is a MOSFET in series with an LED and nine volt battery. The base of the transistor is open and sticking out like an antenna. Changes in the local electric field drive electrons in and out of the base to change the current through the LED. It is very sensitive and can demonstrate the change of electric field with height.

Energy is available from the earth field.  Look up atmospheric motors on the web.

E-Field Detector