Massachusetts Institute of Technology researchers can now predict how much energy solar cells will produce at any location worldwide. Surprisingly, they identified that two types of solar cells (silicon and cadmium telluride) can vary in energy output by 5% or more in tropical regions, where most of the emerging solar cell markets are located. This gap occurs because solar energy can shift depending on local temperature and water in the atmosphere. Their work, appearing December 13 in the journal Joule and developed into an open-source tool, emphasizes that solar products may behave differently depending on their environment.