Search

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 • To predict the final output of a photovoltaic (PV) system, a variety of different types of models are required, like plane-of-array (POA) transposition, module temperature, and others depending on what meteorological data is available. As the data flows through the modeling pipeline, uncertainties can arise. As these uncertainties accumulate, it...

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 • The nominal operating cell temperature (NOCT) cell temperature model is used in the PV performance modeling application SAM and takes the form: $$T_c = T_a + \frac{E_{POA}}{800} (T_{noct,adj} – 20) \left(1 - \frac{\eta_{ref}}{\tau\alpha}\right) \frac{9.5}{5.7 + 3.8 v_{w,adj}}$$ where $$T_c$$ is cell temperature (°C)$$T_a$$ is ambient temperature (°C)$$E_{POA}$$ is the irradiance...

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...

Page • Diffuse radiation from the sky dome is typically divided into several components: the isotropic component, which represents the uniform irradiance from the sky dome;the circumsolar diffuse component, which represents the forward scattering of radiation concentrated in the area immediately surrounding the sun;the horizon brightening component. Published models use different semi-empirical...

Page • These types of models are designed to predict a point (usually the maximum power point ($$P_{mp}$$) or points (e.g., $$P_{mp}$$, $$V_{oc}$$, and $$I_{sc}$$) on the IV curve as a function of environmental variables (e.g., irradiance, cell temperature, and spectral content, for example).

Page • This example uses May 18th, 2014 irradiance data collected at Sandia National Laboratories in Livermore, CA to demonstrate use of the wavelet variability model (WVM). Contents load datadefine variablesrun WVMplot the WVM results load data This file contains two vectors: “GHI” which is the GHI measurements, and “dt” which is...

Page • Precipitation is typically measured using a tipping-bucket rain gauge.  It is usually a cylinder with a known base area that allows precipitation to enter and is directed to a funnel where it fills a very small and sensitive bucket that pivots like a see-saw in such a way that when...

Page • PVPMC published/presented the following in FY22-24: Journal articles A. Livera, G. Paphitis, M. Theristis, J. Lopez-Lorente, G. Makrides, G. E. Georghiou, “Photovoltaic system health-state architecture for data-driven failure detection,” Solar, 2(1), pp.81-98, 2022. https://doi.org/10.3390/solar2010006 https://www.osti.gov/biblio/1855530S. Lindig, M. Theristis, D. Moser, “Best practices for photovoltaic performance loss rate calculations,” Progress in...

Page • Degradation rate (RD) or performance loss rate (PLR) is defined as the decrease of PV power output over time. Although seemingly simple, the estimation of this metric is not trivial when it comes to real operating conditions due to several factors that can influence its calculation. As such, the question...

Page • Field deployment of PV Lifetime systems are located at: Sandia National Laboratories in Albuquerque, New MexicoNational Renewable Energy Laboratory in Golden, ColoradoFlorida Solar Energy Center, University of Central Florida, Cocoa, Florida Most systems are connected to a Pordis 140A String-Level IV Tracer, which automatically collects string IV curves triggered by irradiance...

Page • List of Modules Fielded SiteManufacturerModelCell Technology# of modulesInstallation DateStatusNMTrina SolarTSM-PD05.08 260Wpoly-Si48June 2016NMJinko SolarJKM260P-60 260 Wpoly-Si48June 2016NMCanadian SolarCS6K-270P 270Wpoly-Si48October 2017NMCanadian SolarCS6K-275M 275Wmono-Si48October 2017NNHanwha Q-CellsQ.Plus BFR-G4.1 280Wpoly-Si PERC48October 2017NMHanwha Q-CellsQ.Peak BLK G4.1 300Wmono-Si PERC48October 2017NMPanasonicVBHN325SA16HIT Mono48June 2018NMLGLG320N1K-A5 320W LG NeON2N-PERT Si48June 2018NMMission SolarMSE300SQ5Tmono-Si PERC48May 2019NMItek EnergyIT-360-SE72mono-Si PERC50March 2020NMSolariaPowerXT-400R-PMmono-Si, shingled24October 2021NMLGLG400Q1C-A6mono n-type IBC24October...