Modeling Photovoltaic System Reliability and Performance Using GoldSim
Steven Miller (firstname.lastname@example.org), Joshua Stein, and Jennifer Granata, Sandia National Laboratories
A photovoltaic (PV) system can range in size from a tiny system consisting of a single PV module (commonly called a solar panel) connected to a battery to perform a simple function (such as operating a vehicle gate opener or an overhead parking lot light) to home or business roof top systems to very large utility systems consisting of thousands of modules and dozens of inverters. The PV modules convert the sun's energy to DC electricity, and the inverters convert that DC electricity to AC electricity. A PV system can include many other components as well, including transformers, AC and DC disconnect switches, combiner boxes, and trackers to allow the modules to follow the arc of sun across the sky.
Accurately predicting the performance of photovoltaic PV systems can be a challenging undertaking, but a necessary one in order to assess the financial viability of a PV system. PV system energy production can be affected by numerous factors including the choice of location, component technology, and system design. While these modeling factors are generally considered by most PV performance models, other factors are typically not, including: 1) solar resource variability, 2) degradation due to environmental conditions (humidity, temperature swings, UV exposure, wind, salt spray, rodent damage, etc.), 3) component reliability (failure rates of inverters, modules, trackers, etc.), and 4) operations and maintenance (O&M) strategies.
We at Sandia National Laboratories are using GoldSim software to develop an analytical, scenario-based predictive modeling tool that can be used to help owners, operators, risk managers, and financiers simulate planned PV projects to avoid costly system weaknesses prior to development. Sandia is developing the Photovoltaic Reliability and Performance Model (PV-RPM) with industry partners on behalf of the Solar Energy Technologies Program of the U.S. Department of Energy (DOE).
What is PV-RPM?
Figure 1 shows a conceptual flow diagram for PV-RPM. PV-RPM calculates hourly simulated plant life cycle data including energy production and component availability. System availability—a fraction of the time that the system is available to supply energy—is calculated as a function of time.The PV-RPM allows the user to define a PV system (inverters, modules, tracking, etc.) and select or input weather data, and the model will calculate the performance of the system (kilowatt-hour output of the system) using the SNL Photovoltaic Array Performance Model  and the SNL Performance model for Grid Connected Photovoltaic Inverters . These performance predictions are actually a prediction for an idealized case where the PV system does not experience component failures or degradation, electrical grid outages, or any other type of disruption.
The PV-RPM that we are developing is intended to address more “real world” situations by coupling the performance model with a reliability model so that inverters, PV modules, combiner boxes, etc. can experience failures and be repaired (or left unrepaired). The model can also include other effects, such as PV module output degradation over time or disruptions such as electrical grid outages. Thus, the GoldSim Reliability Module is used to probabilistically model the reliability of the PV system components over the lifetime of the system.
A financial model is currently under development that will calculate cash flow based on such inputs as the initial capital cost of the PV system, monthly debt financing payments, O&M costs, failed component repair or replacement costs, and the revenue generated by the theoretical sale of the produced energy.
Click here to download the GoldSim Player PV-RPM demonstration model from Sandia's web site. Note that the GoldSim Player software is required to run the model and is not included with the PV-RPM model files. You can get the GoldSim Player from the Download section of our web site.
 King, D. L., Boyson, W. E., & Kratochvill, J. A. (2004), “Photovoltaic Array Performance Model,” Sandia Report Number: SAND2004-3535. Albuquerque: Sandia National Laboratories.
 King, D. L., Gonzalez, S., Galbraith, G. M., & Boyson, W. E. (2007), “Performance Model for Grid-Connected Photovoltaic Inverters,” Sandia Report Number: SAND2007-5036. Albuquerque: Sandia National Laboratories.
ACKNOWLEDGMENT: Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
© 2012 GoldSim Technology Group LLC.