Home Power Article
Things that Work! Home Power tests the Solar Pathfinder
Tests Conducted by Richard Perez, Bob-O Schultze and John Pryor
Home Power #16, April/May 1990, pp 44-45.
Placement of a PV array is critical. Determining exactly how much solar energy a specific location receives throughout the year is not easy. Hills, trees, buildings and other obstructions may shade the PV array and reduce its output. And to further complicate things, the Sun's angle keeps changing with the seasons. The array needs to be located at the one place on a site that receives the most sunshine. The Solar Pathfinder is THE tool for this job. It takes all the guesswork out of predicting exactly how much sunshine the array will receive, at a specific site, throughout the year. The Solar Pathfinder is easy to use and accurate enough to measure changes in array position down to a few feet.
How the Solar Pathfinder Works
The Solar Pathfinder uses a highly polished, transparent, convex plastic dome. Reflected in this dome, the user sees a panoramic view of the area around him. All the hills, trees, buildings or other obstacles to sunshine are plainly visible as reflections on the polished surface of the Solar Pathfinder's dome. Since the dome is transparent, the user can also look through the dome to a sun chart within the Solar Pathfinder. This chart shows the Sun's path through the sky for all months of the year. The chart is also calibrated by the hours of the day. The dome has slots in its sides and the user traces the outline of the horizon's reflection of the dome onto the sunchart. The traced line shows exactly at what hours of the day, and months of the year an obstacle will shade the PV array. For example, a sunchart for the array we use told us exactly when the array would be shaded by the hills and trees around us. From this information, we can accurately predict the array's performance at any time of the year...
Using the Solar Pathfinder
This unit is simple to use. First, unpack it from its heavy metal case (this machine is built to travel in the outback for sure). The Solar Pathfinder stands on an adjustable, telescoping tripod. The unit contains a magnetic compass to find magnetic North. The base of the Pathfinder rotates and locks to adjust for magnetic declination — thus corecting for the local difference between true North and magnetic North. The Pathfinder also has a built-in bubble level so the entire unit can be oriented level and facing true South. The user selects the sunchart for his latitude and inserts it into the base of the Pathfinder. The dome goes on top. All that remains is to trace the reflection of the skyline onto the sunchart. The thorough, 27-page manual provided with the Solar Pathfinder shows how to convert the sunchart into specific information about the array's performance... The Solar Pathfinder is very specific and leaves no doubt about the solar insolation situation. The unit comes with suncharts for your latitude.
We found that we wanted to run suncharts in many different locations around our site and compare the amount of sunlight received at each. By doing this, we were easily able to select the best place to put the ground-mounted array. And I mean down to the last foot! No guesswork, no "Well, it looks to me...", just the straight and accurate facts.
Just one observation provides complete info on a site, and the info is adjusted for shading objects and seasonal changes. The Solar Pathfinder can be used anytime of the day, anytime of the year and in either cloudy or clear weather. In fact, we found it easier to see the reflections in the dome when it was overcast, at dawn, or at sunset.
The Info that the Solar Pathfinder Provides
Here is a list of just some of the information that the Solar Pathfinder gives its user. Actual sunrise and sunset times, for each month, at a specific location. Times of the day when objects will shade the site, for each month of the year. Percent of solar radiation available for the average day each month. Percent of solar radiation lost to obstacles due to shadows for each hour and month. Output info is available from the Solar Pathfinder in a variety of units, everything from percents to BTUs per square foot per day.
The fellow, Mr. Bernard Haines, who invented the Solar Pathfinder deserves some kind of award for forward thinking and design. Not only does his device work great, but it's easy to use, accurate, ruggedly built, and just plain ingenious. Cost for the Solar Pathfinder is $255.00 + shipping in the continental USA, and this includes the metal case, tripod, instruction manual and suncharts. Considering that our array cost almost $3,000, the Solar Pathfinder is inexpensive because it allowed us to put the array in the just right place to get its maximum yearlyoutput. Every solar energy user should take the Solar Pathfinder on every job he does. We do. In fact, the Oregon Dept. of Energy requires a sunchart before paying off on the renewable energy tax credits for new PV systems. Even the taxman is hip to the Solar Pathfinder and respects its information. Nuff said...