GEOTHERMAL: The 'invisible renewable' struggles with slow U.S. growth Julia Pyper, E&E reporter Published: Wednesday, April 23, 2014 Geothermal energy is sometimes referred to as the "invisible renewable." Please subscribe to ClimateWire to read the full story. Username: Password: Forgot your access codes? Recover them. Not a subscriber? Sign up for a trial. Ready to subscribe? Click here.