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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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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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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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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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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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 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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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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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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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 increased reflections from the module…

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