Effective irradiance is total plane of array (POA) irradiance adjusted for angle of incidence losses, soiling, and spectral mismatch. In a general sense it can be thought of as the irradiance that is “available” to the PV array for power conversion. In the context of the Sandia PV Array Performance Model (SAPM), effective irradiance ()…

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## Spectral Response

PV devices are characterized by their response to light in a reference spectrum.  When a device is tested in a lab or outdoors, the spectrum of the light source may not be the same as that of the reference spectrum.  The effect of this difference on performance is typically quantified by a spectral mismatch factor.…

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## Single Diode Equivalent Circuit Models

Equivalent circuit models define the entire I-V curve of a cell, module, or array as a continuous function for a given set of operating conditions. One basic equivalent circuit model in common use is the single diode model, which is derived from physical principles (e.g., ) and represented by the following circuit for a single…

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## Point-value models

These types of models are designed to predict a point (usually the maximum power point () or points (e.g.,  ,  , and  ) on the IV curve as a function of environmental variables (e.g., irradiance, cell temperature, and spectral content, for example).

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## Sandia PV Array Performance Model

The Sandia PV Array Performance Model (SAPM) defines five points on the IV curve.  These points are shown in the figure below. The SAPM defines the primary points (, , , and ) with the following equations:            (eq. 1)              (eq. 2)             (eq. 3)               (eq. 4)   Functions: is…

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## Cell Temperature

Cell temperature is required to calculate the IV curve of the module.  Cell temperature is affected by the incident irradiance, weather conditions (such as air temperature and wind speed), and module construction and material properties.

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## Module Temperature

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 30 minutes or more.  Sandia…

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## Sandia Cell Temperature Model

The Sandia cell temperature model estimates cell temperature from module temperature, , plane of array irradiance, , and a temperature difference parameter, . This difference parameter defines the temperature difference between the module and cell temperature. The model form is: , where is a reference irradiance (1000 W/). Content contributed by Sandia National Laboratories  …

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## Sandia Module Temperature Model

Sandia proposes the following model to estimate module temperature, :  = Solar irradiance incident on the module (POA) (W/m^2)  = Ambient air temperature (°C)  = Wind speed (m/s) a and b are parameters that depend on the module construction and materials as well as on the mounting configuration of the module.  The table below lists…

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## Shading, Soiling, and Reflection Losses

Here, irradiance incident on the array (calculated in the previous step) is further reduced by shading, soiling, and reflection losses.  Various modeling approaches have been developed to account for these reductions.  They will be examined in detail in the following sections.

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