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Page • Data from Annex 1 of the IEA PVPS Task 13 report entitled: Climatic Rating of Photovoltaic Modules: Different Technologies for Various Operating Conditions (30120 downloads ) The data set consists of two parts: 1. Module performance data Pmax, Isc, and Voc matrixTemperature coefficient α, β and δSpectral response curveAngular loss...

Page • Bill Marion from NREL developed a correction method that improves the ability of PVWatts to represent the nonlinear behavior at low irradiance, which is evident in x-Si module performance (Marion, 2008). Figure from Marion (2010) presentation: “Overview of the PV Module Model in PVWatts” Marion found that the error could...

Page • Unless the PV array is mounted on a two-axis tracker, the incident angle for the direct component of the solar radiation will not be normal except for a few rare instances, depending on the orientation.  When the angle of incidence is greater than zero, there are optical losses due to...

Page • Before a PV Lifetime system is installed all the modules are characterized indoors on a flash simulator at standard test conditions (STC).  Every year afterwards a sample of modules are removed from the arrays and re-characterized.  All this data will eventually be made available. Guidelines for determining the relationship between...

Page • Inverter saturation, commonly referred to as “clipping”, occurs when the DC power from the PV array exceeds the maximum input level for the inverter.  In response to this condition, the inverter typically adjusts DC voltage to reduce the DC power.  This is done by increasing voltage above the MPP voltage,...

Page • Weather and irradiance data are used as input to PV performance models.  These data are directly measured, derived from measured data, or simulated using a stochastic model. Irradiance is to power as insolation is to energy.  Or in other words: Irradiance is an instantaneous measurement of solar power over some area.  The units of irradiance are watts per...

Page • The isotropic sky diffuse model is the simplest of the POA sky diffuse models and forms the foundation upon which more accurate models build.  The isotropic sky diffuse model assumes that the diffuse radiation from the sky dome is uniform across the sky.  The POA sky diffuse irradiance ($$E_{d,iso}$$) is...

Page • Gantner Instruments  (Juergen Sutterlueti, https://www.gantner-instruments.com/applications/energy/pv-testing-solutions-weather-prospecting/) and Steve Ransome (www.steveransome.com), using outdoor IV measurements on a wide variety of module technologies have developed a PV module performance model based on defining loss factors that affect the shape of the IV curve.  Details of this model can be found on publications listed on Ransome’s website.

Page • Grid connected inverters must be able to reliably detect a loss of grid condition and rapidly disconnect from the grid system.  This behavior prevents the formation of an unintentional island (a stand-alone power system with its own generation and loads operating in balance).  Current standards (e.g., IEEE 1547 and IEC...

Page • A series of papers by Martin and Ruiz (2001; 2002; 2004) describe the optical reflectance loss for PV modules and model the effect of these losses on annual energy. Martin and Ruiz (2001) establish that the angular losses (AL) of a PV modules are a function of the solar incident...

Page • Each PV device (e.g., cell, module, string) in operation will have a maximum power point ($$I_{mp}$$ and $$V_{mp}$$) for the ambient operating conditions of incident irradiance and device temperature. Even at the same irradiance and temperature, seemingly identical devices will not have the same maximum power point because of small manufacturing differences....

Page • The objective of performance modeling is to predict the expected output of a solar system given 1) the system design, and 2) the environment in which it is operating, including the solar resource.  A performance model is actually a collection of submodels, which calculate different quantities needed for determining output...

Page • This modeling guide is a series of pages that describe the PV performance modeling process from defining weather, irradiance, and module and system design inputs to models used to calculate irradiance on the plane of the array, module temperature, IV curves, and system output power. The navigation menu guides you...

Page • Measuring or predicting module temperature is the first step in estimating cell temperature, which is needed predict the module IV curve.  Module temperature depends on a number of factors, including air temperature, irradiance, wind speed, and module materials.  Most models are steady-state and therefore appropriate for time steps of about...

Page • Similar to the Performance Ratio, the ratio of the power (DC or AC) to the DC STC power rating compared to the irradiance divided by the reference irradiance gives the normalized efficiency, $$\eta_N$$ [1]: $$\eta {_{N}}=\frac{P/P_{STC}}{E_{POA}/E_{ref}}$$ where P is the measured power, $$P_{STC}$$ is the STC rated power, $$E_{POA}$$ is the plane of array irradiance, and $$E_{ref}$$ is...

Page • Some inverters will automatically decrease their efficiency under conditions of elevated temperature.  This behavior is meant to protect the device from conditions that might lead to component failures.  There is currently no standard test procedure to characterize this behavior for inverters.  In the future, inverter performance characterization should include information...

Page • Sandia is building an outdoor bifacial PV performance test bed in Albuquerque, NM to collect data to be analyzed and shared with the community. This data will be used to develop predictive performance models that can eventually be included in commercial applications. Based on a review of literature on this...

Page • While the sky diffuse model presented up to this point separated the isotropic, circumsolar, and horizon components explicitly, Perez developed a more complex model that relies on a set of empirical coefficients for each term. The basic form of the model is: $$E_{d}=DHI\times \left[ \left( 1-F_{1} \right) \left( \frac{1+\cos \left...

Page • The performance index is the ratio of measured energy from a PV system to the predicted energy using a PV performance model.  Unlike with the performance ratio, the performance index very close to 1 for a well functioning PV system and should not vary by season due to temperature variations....

Page • The daily AC performance ratio ($$PR_{AC}$$) is defined in IEC 61724 as: $$PR_{AC}=\frac{Y_{fAC}}{Yr}$$ , where: $$Y_{fAC}$$ is ths the AC system yield defined as the measured AC energy produced by the PV system in the day (kilowatt hours per day) divided by the rated power of the PV system.  The definition of this...

Page • The physical model for the incident angle modifier is based on Snell’s and Bougher’s laws, and was published by De Soto et al. (2006).  Our presentation here includes correction to a few errors present in that paper.  The first step is to calculate the angle of refraction ($$\theta_r$$) using Snell’s law. $$\theta_{r}=\arcsin...

Page • Decomposition models are used to estimate DNI from measured GHI. The following three simple fitted models were developed from hourly average observations of GHI, DNI, and DHI. These models are based on the clearness index $$k_t$$ and the diffuse fraction $$k_d$$. $$k_t=\frac{GHI}{E_a \cos(Z)}$$, where $$E_a$$ is extraterrestrial irradiance on a plane normal...

Page • In this step the irradiance data is transposed to the plane of the array.  The sub-models included in this step include various array tracking algorithms, estimates for the reflectivity of the ground (albedo),  and models to calculate the diffuse irradiance on the array from the sky. The calculation of the...

Page • The plane of array (POA) beam component of irradiance is calculated by adjusting the direct normal irradiance $$(DNI)$$ by the angle of incidence ($$AOI$$) in the following manner: $$E_b=DNI\times\cos\left(AOI\right)$$. Content contributed by Sandia National Laboratories

Page • Irradiance on a tilted surface that is reflected off the ground, $$E_g$$ , is calculated as a function of the irradiance on the ground, usually assumed to be $$GHI$$, the reflectivity of the ground surface, known as albedo, and the tilt angle of the surface, $$\theta_{T},{surf}$$ : $$E_{g}=GHI\times albedo\times\frac{\left(1-\cos\left(\theta_{T},{surf}\right)\right)}{2}$$ The model for ground reflected irradiance $$E_g$$ develops from the following...