Solar Site Assessment: Page 3 of 3

Beginner

Inside this Article

Solar Pathfinder
Solar Pathfinder’s dome reflects the horizon over a sun-path diagram.
SolarPathfinder sun-path diagram
A horizon line sketched onto the sun-path diagram allows for manual computation of solar exposure.
SolarPathfinder Assistant software
A digital photo of the Pathfinder’s dome can be imported into the Assistant software to produce shade analysis reports.
PV array with a chimney creating shade
Architectural details, such as shed dormers and chimneys, can create shade during certain times of the day and reduce a PV system’s production.
Wiley Electronics' Acme Solar Site Evaluation Tool (ASSET)
The ASSET makes quick work of shooting a panorama of photographs.
ASSET software
Yearly solar data and shading factor are calculated by ASSET’s software.
ASSET panoramic image from site photos
A single panoramic image stitched together from the site photos and overlaid with a sun path.
The Solmetric SunEye
The Solmetric SunEye uses a fish-eye lens to shoot a 360° photo.
Solar Pathfinder
SolarPathfinder sun-path diagram
SolarPathfinder Assistant software
PV array with a chimney creating shade
Wiley Electronics' Acme Solar Site Evaluation Tool (ASSET)
ASSET software
ASSET panoramic image from site photos
The Solmetric SunEye

If You Can’t Escape the Shade

Partial shade and reduced power production affect different systems in different ways. In a stand-alone (off-grid) PV system, even minimal shading can have a big impact. Since shading reduces energy production, this may necessitate more careful load management (reducing energy consumed) or, if a generator is used, increased run-time (and the associated fuel consumption, pollution, and maintenance). If shade affects your PV system’s winter production, perhaps a hybrid PV-wind or PV-hydro system could be a solution.

For a grid-tied PV system, partial shading is not as critical—it will merely reduce the amount of utility power the system offsets. All of the mentioned site analysis tools can estimate energy loss due to shade. Because it is important to create realistic energy estimates, these losses should be factored into the amount of projected annual energy production for a grid-tied system. In some cases, you may be able increase the array size to offset the losses due to partial shading.

Given the knowledge and tools to perform a proper solar site analysis, PV system designers can ensure that their systems will not suffer needless energy reduction due to shade. PV systems are substantial financial investments and can only produce electricity if they have sunlight to work with, so it makes sense to make sure they are properly placed to maximize your green energy and your wallet power.

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Justine Sanchez is a NABCEP-certified PV installer, Home Power Technical Editor, and Solar Energy International instructor. Justine lives, works, and teaches from an on-grid, PV-powered home in Paonia, Colorado.

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