Researchers have constructed a photovoltaic cell that harvests energy from the environment during the day and night, making use of the heat leaking from Earth back into space. At night, solar cells radiate and lose heat to the sky, reaching temperatures a few degrees below the ambient air. The device under development uses a thermoelectric module to generate voltage and current from the temperature gradient between the cell and the air. The setup is inexpensive and, in principle, could be incorporated within existing solar cells.
