In 1839, Alexandre Edmond Becquerel discovered the photovoltaic effect, which explained that electricity could be generated from sunlight by shining light on an electrode submerged in a conductive solution. However, solar cells remained very inefficient until later research and development, and were mainly used for measuring light. The first solar house, built in 1939 at MIT, used seasonal thermal energy storage to provide year-round heating from solar power. Fossil fuels like coal, oil and natural gas also originate from ancient sunlight.