Sandia National Laboratories (SNL) plays a leading role in the development and application of photovoltaic (PV) technology used for generating electricity. These efforts include research, development and performance modeling of crystalline silicon, thin-film, concentrating PV, and inverter technologies and working to transfer this knowledge to end-users in a way that will increase the utilization of PV systems for generating electricity. In order to support this work, SNL has been instrumental in developing computer modeling tools that can be used to design, monitor and predict PV and energy storage system performance for specific research needs. Some of these tools have been incorporated into third-party software that includes both free and commercial applications, while others have been developed and applied exclusively by researchers at SNL.