Is there a clear explanation of Packing Factor (an option in the solar Array page)?

For the PV component-based models, SAM uses the packing factor on the Array page to calculate the number of acres of land required for the project. When you specify a non-zero land cost in $/acres on the System Costs page, SAM uses the number of acres to calculate the land-related costs, which contribute to the total indirect cost. For a rooftop system, an appropriate value for land area would be zero.

Best regards,
Paul.

SAM calculates the total land area by multiplying the packing factor by the total module area and converting it to acres. The calculation is explained in the Help topic for the Array page.

For example, the default Photovoltaics, Commercial case has a total module area of 1477.87 m2 and a packing factor of 2.5 (from the Array page). SAM shows the land area in acres as a calculated value on the Array page and the PV System Costs page: Total land area = 1477.87 m2 x 2.5 / 4,047 m2/acre = 0.91 acres.

The packing factor only affects the results of your simulation if you specify either land or land preparation cost in $/acres on the PV System Costs page. In the default case, both of these variables are zero, so the packing factor does not affect the results.

The packing factor is designed to be used for large, ground-mounted systems where land area-related costs are a factor.

If land-related costs are important for your analysis, you may want to research the relationship between total module area and land area for different installed systems to get a sense of what value to use for your analysis.

Unfortunately, the term "packing factor" is also sometimes used to describe the density of solar cells in a PV module, which is a different use of the term than in SAM.

Best regards,
Paul.