Aron P. Dobos

Validation of multiple tools for flat plate photovoltaic modeling against measured data

In this validation study, comprehensive analysis is performed on nine photovoltaic systems for which NREL could obtain detailed performance data and specifications, including three utility-scale systems and six commercial-scale systems. Multiple photovoltaic performance modeling tools were used to model these nine systems, and the error of each tool was analyzed compared to quality-controlled measured performance data. This study shows that, excluding identified outliers, all tools achieve annual errors within ±8% and hourly root mean squared errors less than 7% for all systems. Finally, the acceptability of this range of annual error is discussed with regard to irradiance data uncertainty and the use of default loss assumptions, and two avenues are proposed to reduce photovoltaic modeling error.

System Advisor Model: Flat Plate Photovoltaic Performance Modeling Validation Report

The System Advisor Model (SAM) is a free software tool that performs detailed analysis of both system performance and system financing for a variety of renewable energy technologies. This report provides detailed validation of the SAM flat plate photovoltaic performance model by comparing SAM-modeled PV system generation data to actual measured production data for nine PV systems ranging from 75 kW to greater than 25 MW in size. The results show strong agreement between SAM predictions and field data, with annualized prediction error below 3% for all fixed tilt cases and below 8% for all one axis tracked cases. The analysis concludes that snow cover and system outages are the primary sources of disagreement, and other deviations resulting from seasonal biases in the irradiation models and one axis tracking issues are discussed in detail.

Economic competitiveness of U.S. utility-scale photovoltaics systems in 2015: Regional cost modeling of installed cost (

Utility-scale photovoltaics (PV) system growth is largely driven by the economic metrics of total installed costs and levelized cost of electricity (LCOE), which differ by region. This study details regional cost factors, including environment (wind speed and snow loads), labor costs, material costs, sales taxes, and permitting costs using a new system-level bottom-up cost modeling approach. We use this model to identify regional all-in PV installed costs for fixed-tilt and one-axis tracker systems in the United States with consideration of union and non-union labor costs in 2015. LCOEs using those regional installed costs are then modeled and spatially presented. Finally, we assess the cost reduction opportunities of increasing module conversion efficiencies on PV system costs in order to indicate the possible economic impacts of module technology advancements and help future research and development (R&D) effects in the context of U.S. SunShot targets.

/W) and LCOE (

Accurate modeling of a photovoltaic modules current-voltage characteristic is essential to predicting the generated power at any operating condition. This paper presents an approach to improve prediction accuracy of current single diode models by leveraging test data collected according to the IEC-61853 standard. Modified auxiliary diode model equations are proposed, along with a procedure to automatically calculate the additional model parameters from test data. The extended single diode model indicates potential to reduce average maximum power point prediction error across a wide temperature and irradiance range by about 75 % relative to the baseline five parameter model.

/kWh)

This paper describes a straightforward methodology for modeling photovoltaic arrays comprised of variously configured sub-arrays connected to a single inverter. Particularly in rooftop applications, PV arrays must be installed within the constraints of various roof slopes and geometries. This reality calls into question the typical modeling assumption that each panel operates at its maximum power point, even when shading effects are ignored. A series of scenarios are presented with a variety of array orientations, string configurations, and temperature effects. Each scenario is modeled in detail using industry standard modeling tools, and the operation characteristics and DC losses due to sub-array layout mismatch are presented. Typical losses resulting from sub-optimal relative alignment of fixed array layouts are on the order of a one percent or less on an annual basis, suggesting that sub-array orientation in the absence of shading is not a major factor in small to medium scale system energy yield.

Procedure for applying IEC-61853 test data to a single diode model

The use of the term “availability” to describe a photovoltaic (PV) system and power plant has been fraught with confusion for many years. A term that is meant to describe equipment operational status is often omitted, misapplied or inaccurately combined with PV performance metrics due to attempts to measure performance and reliability through the lens of traditional power plant language. This paper discusses three areas where current research in standards, contract language and performance modeling is improving the way availability is used with regards to photovoltaic systems and power plants.