The photovoltaic array shading model simulates the effect of structures, vegetation, or objects surrounding the array that may block the sun at different times throughout the day and year. The shading model is not designed to represent inter-array (module-to-module) shading or strategies for avoiding it such as backtracking.

The shading model uses a 24-by-12 matrix to assign a shading factor to each hour of the day for each month of the year. Each shading factor is a value between zero and one that represents the fraction the direct normal solar radiation allowed to reach the array in a given hour. A shading factor of one represents no shading. A shading factor of zero represents complete blockage of direct normal radiation from the array.

Solar Advisor assumes that shading reduces the magnitude of the direct normal component of the global radiation incident on entire array over an hour. For example, a shading factor of 0.90 for an hour when the value of the direct normal incident radiation is 200 W/m2 and the diffuse incident radiation is 10 W/m2 would result in a global incident radiation value of 0.90 × 200 W/m2 + 10 W/m2 = 190 W/m2 for that hour.

Note that for flat-plate photovoltaic arrays, solar advisor calculates the array output based on the value of the global incident radiation, which is equal to the sum of the normal and diffuse incident radiation components. For concentrating photovoltaic (CPV) arrays, on the other hand, the array output is calculated based only on the value of the direct normal incident radiation component.

Because Solar Advisor assumes that shading affects the entire array uniformly, it cannot model partial shading of the array or of individual modules within the array. The shading model does not consider factors such as string layout, location of blocking diodes, or cell layout in individual modules.

Enabling and Disabling Array Shading

Solar Advisor allows you to enable and disable array shading so that you can turn off array shading after defining a shading matrix without losing the values in the matrix.

Note. Shading factors must be enabled for Solar Advisor to use the data in the shading matrix.

Defining the Shading Factor Matrix

To define the shading factor matrix, you assign a value to each cell in the matrix. The shading factor in a cell applies to a given hour for an entire month. For example, a shading factor of 0.90 in the 6 a.m. cell for May would mean that 90% of the direct normal radiation value in the weather file for each hour beginning at 6 a.m. and ending at 7 a.m. in May would be used to calculate the global solar radiation incident on the array.

Note. The time convention for the matrix is determined by the convention used in your weather file. For example, TMY2 and TMY3 data use local standard time.

As you work with the shading factor matrix, keep the following in mind:

To define a shading factor for a single cell:

To replace the value in a cell, click the cell and type a replacement value.

To delete the value from a cell, double-click the cell and press the Delete key.

To define a single shading factor for multiple cells:

Select the cells to which you want to apply the shading factor.

Type a value between zero and one.

Press the Enter key or click Apply to selected cells.

 

 

Importing and Exporting Shading Factor Data

Solar Advisor allows you to import and export the shading factor matrix as a comma-delimited text file that contains 12 rows of 24 hourly shading factors separated by commas. The file should not have row or column headings.

To export the shading matrix as a text file, click Export.

To import a data from a comma-delimited text file, click Import