Rackability: A sophisticated measure of utility-scale site viability - Solar Power World

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By SPW | February 10, 2021

PVSketch Mega from PVComplete computes total rackable area and provides the numerical m² computation together with a visual depiction of the rackable area on both the site plan and topographic map.

By Olivia McShea, head of sales and marketing, PVComplete

When considering the viability of a utility-scale tracker or fixed-tilt project site, there are many factors that inform site selection. But until now, it’s been difficult to quickly determine, with precision, exactly how much of the land is “rackable.” In other words, there hasn’t been a means to compute the percentage of total land area on which mounting systems can actually be installed.

Utility-scale project developers can now take advantage of an important new early-stage site assessment tool to achieve a reliable rackability measure. Today’s most sophisticated utility-scale solar design software is able to compute a site’s rackability with only three basic project inputs, including:

Site plan obstructions

First, identify those areas on which, irrespective of terrain, racking isn’t desired or can’t be installed, including building footprints, treelines, roads and unsuitable land such as a marsh or wetland. Using utility-scale solar design software, it is possible to draw obstructed areas within the site boundary to be subtracted from the total site area. Traditionally, the only way to account for the impact of obstructions on usable site area has been to eyeball physical obstructions and approximate them in a layout. Now, software can compute an accurate quantitative measure before any layout is created.

Slope thresholds — East/West and North/South

Advanced solar software takes into account priorities related to both East/West and North/South slope thresholds when computing rackable area. Understanding where a site requires no grading or other alterations to accommodate racking is vital to assessing project costs and site capacity upfront.

Slope threshold choices can support project goals. When trying to maximize system size, E/W slope thresholds may be higher in order to fit more modules. For systems that prioritize system production, designers may choose to limit the E/W slope threshold to ensure there is no excessive row-on-row shading.

Additionally, the preferred tracker or fixed tilt model may have a max slope limitation that impacts the viability of tracker placement. For instance, longer trackers may have a lower N/S slope threshold. In this instance, project developers may not want to install any trackers on land that has a max slope greater than, for example, 15° in any cardinal direction to avoid grading costs. Terrain with a slope that is greater than the max specified would be marked as a keep out area and subtracted from the total rackable area.

Minimum contiguous area

The final rackability input is a measure of the minimum contiguous area required to meet the project goals. In other words, what matters most is not the total site square footage, but rather the number of square feet required to fit a tracker or partial tracker. Minimum contiguous area indicates the minimum amount of unbroken space that must be within all other site thresholds to be rackable area.

As with slope tolerances above, project goals matter. If system size is the driver, placing partial trackers wherever space permits is desirable. In that case, the minimum contiguous area would be smaller. Alternatively, developers may want to minimize equipment costs, and therefore avoid placing any trackers unless space permits to install a full block of trackers. In that case, the minimum contiguous area would be larger.

With these three inputs, sophisticated utility-scale solar software takes the computation of rackable area from a best guess to a tangible number, and delivers a measure of early-stage project viability to inform site selection before investing valuable design time for large scale solar projects.

Olivia McShea oversees PVComplete’s sales and marketing efforts. As the lead point of contact for PVComplete customers, she assists solar companies in getting started, training sessions and continued support. She also facilitates companies finding custom software solutions through PVComplete. Additionally, Olivia acts as liaison for residential, commercial and utility scale design services.