Solar Energy (Photovolatics)
Aim/Objective: Solar photovoltaic (PV) power is becoming a viable investment in Alaska and other northern latitudes due to decreasing costs, low maintenance needs, and unique performance characteristics. This project analyzes the accuracy of solar PV production modeling performed with Typical Meteorological Year (TMY) solar irradiance data in Alaska. Due to Alaska’s northern latitudes, most satellite-based irradiance data sets that are available to the rest of the continental United States cannot be reliably used to predict solar PV system outputs. Installers and developers continue to use TMY data to estimate system outputs for planning and decision making. This project systematically quantifies how well outputs are modeled relative to measured values for 25 solar PV installations across Alaska using PVWatts with input TMY irradiance data.
Methods: Measured solar PV system production for 25 solar PV systems was compared on a monthly basis to modeled production using PVWatts. Production was measured using reported energy production from system inverters. Modeled outputs from PVWatts were generated using both TMY2 and TMY3 irradiance data sets. Installations ranged in size from 2.6 kW – 18.0 kW. While these systems are small for the rest of the United States, systems larger than 100 kW were only installed for the first time in Alaska in 2018 and were not included in this study.
Results: PVWatts outputs sourced from TMY3 irradiance data corresponded most closely to measured energy outputs for the selected solar PV installations. Further comparisons indicated PVWatts outputs had significant monthly variations in model accuracy. Modeled outputs for the months of November through February were over 100% greater than measured outputs. Modeled outputs for the months of April through September were within 10% of measured values excluding the August TMY3 modeled output (13%).
Conclusion: The effort to improve performance modeling for Alaska solar PV systems continues, and these results have been further validated by new larger installations that have been installed in 2018. Further analysis to compare NASA POWER satellite solar irradiance data to measured solar irradiance data and solar PV system production is ongoing. This effort will eventually lead to an improved solar irradiance data set that will reduce system production uncertainty with respect to solar PV system modeling and design.