When evaluating a site for a solar heating or photovoltaic installation, there are many features of the site to take into account. The latitude and longitude establish the sun’s path. The orientation of the collector array, the tilt and azimuth, defines the field of view of the sun. Shading from obstructions, such as trees and buildings, decreases exposure to the sun’s radiation. Local and regional weather patterns also must be taken into consideration.
Solar site evaluation tools use these factors in determining the best location for optimum solar exposure. Three of the leading solar site evaluation tools used by the solar energy industry are Solar Pathfinder, Acme Solar Site Evaluation Tool and Solmetric SunEye.
Solar Pathfinder includes a transparent plastic dome, instrument platform, base section, tripod legs and paper sunpath diagrams and is easy to quickly assemble. Solar Pathfinder Assistant software is also available for use in conjunction with the Solar Pathfinder unit. The sunpath diagram for the specific latitude of the site is placed on the instrument platform and under the plastic dome. Looking down onto the dome, the site evaluator can see a panoramic view of the site reflected on the surface of the dome. Since this view is a reflection instead of actual shadows, the Solar Pathfinder can be used anytime of day in any type of weather. Any obstructions to the sun’s rays are visible in the reflection. Openings in the side of the plastic dome permit the evaluator to trace the outline of the obstructions on the sunpath diagram, thereby indicating what areas of the site will be shaded. A digital photograph may also be taken and uploaded into the Solar Pathfinder Assistant software program. The software identifies the shading patterns, merges them with solar radiation data and local weather records (from the National Renewal Energy Laboratory) and mathematically calculates the potential percentage of solar radiation of the site.
Acme Solar Site Evaluation Tool, also known as ASSET, consists of a precise positioning system, a digital camera, and accompanying software. After the site evaluator levels the positioning system, the digital camera will take a set of photographs from nine positions. The software will then generate a composite panoramic photograph and add an overlay of the path of the sun. Using the historical solar radiation and weather of the site (from the National Renewal Energy Laboratory), the software will perform a shading analysis of the photograph and determine the quantity of solar radiation that can be predicted.
Solmetric SunEye is an integrated hand held electronic device and includes a touch screen interface, a fish-eye lens, a digital camera and measurement software. The digital camera automatically photographs a panoramic view of the entire horizon, identifying the obstructions. The site location’s sunpaths are created. After taking past regional weather into account, the Solmetric SunEye will generate reports and bar charts showing shading percentages and expected solar exposure of the site.
Which one of these solar site evaluation tools is the best? The Solar Pathfinder is the only one requiring assembly, which may be inconvenient for the site evaluator. It also may not be as accurate since site evaluators may not always position their digital cameras in the precise location over the plastic dome. The Solar Pathfinder does, however, have the advantage of being able to be used during any time of day or weather. The Solmetric SunEye, being a hand held device, may lack the stability of a stationary device and possibly not be as accurate. In addition, the weather data used is regional, not local to the site, and is not acquired from the National Renewal Energy Laboratory. The Solar Site Evaluation Tool seems to be the most convenient of the three for the site evaluator, although the quality of the photos may be compromised by sun and weather conditions. However, it is perhaps the most accurate of the three evaluation tools.
The costs for these units varies tremendously. The Suneye is the most expensive coming in around $1,300. The asset at just over $500 and the Pathfinder at around $300. Each of the tools can do the job well but the only question is how easily they do the job. If you are looking for gee whiz then the Suneye has it. If you are just looking to get the job done professionally I would recommend the pathfinder with your own digital camera.