As solar power becomes a larger source of electricity and power for locations, it becomes increasingly important to fully understand and predict the power output of solar modules over their entire lifetime. Traditional solar module degradation tests are done under accelerated exposure environments, where the conditions are more aggressive than an outdoor environment, with the intent of testing the lifetime performance of a module within a more reasonable time scale. While these tests are certainly important, they can be either over or inadequately aggressive; therefore it is also critical to monitor real-world,outdoor power plants degrading under actual real-world exposure conditions. A combination of the two methods provides the best rate of change (ROC) or lifetimeperformance prediction of PV power plants, with indoor exposures degrading modules in a shorter time span, and outdoor modeling giving insight into the actual degradation patterns of systems and providing a comparison, by cross-correlation, of accelerated and real-world degradation.