Mechanical Design The physical assembly of the array is one of the most important parts of designing a high-performance system.

Mechanical Design

The physical assembly of the array is one of the most important parts of designing a high-performance system.

The mechanical design attributes are the most visible parts of a solar array: which modules are used, how many are
 installed, and how they are structured & oriented.

// Module Choice

The specific module used on a project has a major impact on the overall design. The module form factor (size and weight) will determine the number of modules that can be designed on a system. The efficiency of the module (and therefore the module’s rated power) determine the nameplate power for the system. And finally, the voltage and current rating of the module determines the electrical system designs, including how many modules can be wired in series, and how the strings must be fused. And of course, the cost of the module is a major driver in determining a project’s financial returns.

Additionally, other factors, such as temperature coefficient, fill factor, low-light performance, and binning tolerance, can all have an impact on a system’s energy performance. The relative importance of these factors will depend on the size and location of an array.

Solar Module Specifications 

Source: Trina Solar

// Module Orientation

A module’s orientation in a fixed-tilt array is given by its tilt and azimuth angles. These two measures define the direction of the collector’s face:

• Azimuth defines the direction on a compass that the module is oriented. A zero degree azimuth corresponds to due North, 90 degrees will face East, 180 degree azimuth corresponds to due South.
• Tilt defines the angle of incline of the module, with zero corresponding to completely flat, and 90 degrees corresponding to completely vertical.

Module Tilt and Azimuth Angles 

Source: Homepower Magazine

The most common orientation for a solar array would be an azimuth of toward the equator (180 degrees in the Northern Hemisphere) and a slight tilt (tilt of between 5-20 degrees). In some systems, such as tracked systems, these angles will change throughout the day based on the position of the sun.

// Row-to-Row Spacing and Ground Coverage Ratio

In commercial rooftop and ground-mount arrays, the spacing between the rows of modules is a critical design decision, as it has implications for the system size (since tighter spacing means that an array can fit more modules in a given space), and row-to-row shading (since closer racks of modules will shade each other more often).

A common design metric to evaluate the module spacing is the Ground Coverage Ratio (GCR), which is the ratio of the total module area, divided by the total ground area of the array. GCR values will be below 1.0, often between 0.3 and 0.7. There is an inverse relationship between row-to-row spacing and GCR: as the rows are spaced more closely together, the site ground coverage ratio will increase.

As GCR changes, there is generally a trade-off between a system’s nameplate size and its energy yield. Lower GCR values will keep modules spaced far apart, which maximizes their individual production – however, this will result in a smaller-sized system. Higher GCR values will increase the system size, but will reduce the energy yield from higher cross-bank shading.

Array Row Spacing 

Source: Homepower Magazine

// System Sizing

The size of a solar array indicates how much power it can deliver at peak conditions. The power level is often referred to as the “nameplate power” of the array. System sizes are typically given in two different values: the DC power (the number of modules multiplied by their STC power rating), and the AC power (the number of inverters multiplied by their maximum rated AC output power). The ratio between the DC power and AC power is called the “Inverter loading ratio” (ILR).