ROOF AREA

For systems mounted flush against tilted roofs, determining the required area is very straightforward. In this case, because the modules are not tilted off the roof surface and therefore will not create shade, they can be mounted adjacent to each other. For these flush-mounted systems, the required space works out to between 60 and 80 square feet per kilowatt of array, depending on which module is used.

The roof space required for a tilt-up array on a flat roof depends on the type of modules used, the desired tilt angle, and any restrictions on the height of the tilt-up array.

A module's efficiency indicates the amount of wattage it produces for a given surface area. All the brands we use are of very high quality, but they vary in efficiency. SunPower modules have the highest efficiency on the market, so this is the module of choice for situations where roof space is a limiting factor. If there is plenty of roof space, a less efficient (and less costly) module is often used.

The more steeply a row of modules is tilted, the longer the shadow it casts behind it. This requires that the next row, or "sub-array" of modules be spaced far enough back that it won't get shaded by the front sub-array.

The area required for a given array size can also be affected by height restrictions. The height of a roof-mounted tilt-up array can be limited by wind-load, zoning, and/or aesthetics. Finally, most commercial roofs have a significant amount of HVAC, piping, and other obstacles on the roof. A PV array must be designed and installed around these obstacles and the shade they create.