Solar Pathfinding

by Ben N on December 17, 2016


The last two days, I was working with my friend, Kurt. Kurt and his wife, Monica, helped out on the garage a little while back when I was putting in the Pex tubing for the hydronic heat. Kurt mentioned that Monica had a Solar Path Finder. I asked if I could borrow it, and sure enough, the next day Kurt had brought it with him.

So, today, I got to use the Solar Pathfinder.

In essence, the Solar Pathfinder is an optical tool which makes a circular reflection of the trees, buildings, and other obstructions which may block your access to sunlight through the year. I used a Solar Pathfinder once before in a class, so I only needed a quick review through the manual before heading outside.

IMG_2445The device sets up on an included tripod. There’s also a bubble level to make sure it’s oriented nice and level. The first main thing to do is orient the Pathfinder due south. That’s pretty easy to do since there’s a compass built right in. It even accounts for magnetic deviation. If you are somewhere that True North and Magnetic North don’t quite line up, the compass can be adjusted to compensate for that. Where I am in the Midwest, the lines of magnetism point straight north, so I didn’t have to make any adjustments.

With the Pathfinder pointed straight south, I laid in place the piece of black paper that comes pre-printed with lines marking both the time of day and height of the sun at each month. (More than one diagram is included. I used the one that most closely lined up with my latitude.) On top of that, I placed the smoked plastic dome. Looking at the dome, I can see both the reflections in the dome AND the white markings on the paper UNDER the dome.

Looking straight down at the dome, the bubble level is right in the middle, and reflects straight back up. The edge of the dome is the horizon, with south at the top and north at the bottom. The left and right edges are the eastern and western horizons.

I outlined the trees by reaching under the dome with a white grease pencil. There’s space designed to reach through with the pencil.

Solar Pathfinder w graphics_largeAfter I had done that, I headed back inside to take a look at my tracing. The markings on the paper list what percent of the sun’s energy is in that hour during that month. I added up the percent of all the hours in which the sun was NOT blocked by trees. When the sun is highest in the sky – May, July, and June, trees only block the sun very early and late in the day. And when the sun is blocked, it’s only a very small percentage of the total daily sun energy. During those sunny months, the sun would be directly shining on my solar panels 92% of the time.

April and August give me 84% of the maximum solar energy.

Spring and fall, the numbers aren’t quite as good. A row of maple trees (belonging to my next door neighbor) blocks the sun in the late afternoon. Of course, a month like March will be a little better than September. In March, there aren’t any leaves on the trees yet, whereas in September the leaves haven’t fallen off yet. By October and February, I’m only getting 75% of the maximum solar energy.

In December, solar is at it’s absolute worst. The sun is just SO low in the sky that shadows stretch impossibly long. According to the Pathfinder, I might be down to as little as 25% of my maximum solar. The only upside is that all the trees in view are deciduous, (other than that pine tree right in the middle,) so at least there’s no leaves on them in the winter. ┬áThen again, by February, that pine tree no longer reaches the garage. It’s also this same time of year that it’s completely possible for the solar panels to be simply covered with snow, producing essentially NO solar energy.

Solar-Pathfinder_sunnyThe important thing to remember is that MOST of the solar energy comes from the middle of the day and the summer season. So, do I have perfect solar access? No, I don’t. Ideally, you almost want to be in the middle of an empty field. I’m in a neighborhood, but at least I don’t have a great big tree right next to my garage! (Anymore.)

The other thing to remember is that I made this Solar Pathfinder tracing from THE GROUND. While my solar panels will be on the ROOF of the garage, I couldn’t figure out any convenient and safe way to do that at the moment, while we are in a brief pause between two snow storms. With the solar panels higher in the air, they will be LESS effected by the shadowing objects. If you look at the video I shot the other day, there’s clearly some times where shadows fall on the front of the garage (where the Solar Pathfinder was) but not on the ROOF of the garage.

The Solar Pathfinder didn’t really tell me too much new. I already knew that I’d lose some energy in the afternoons in the summer because of my neighbor’s tree-line. I also knew that the distant pine tree could reach the garage during those shortest days of the year. Using micro-inverters will help somewhat with shading in that only the shaded panel will stop producing energy. The others will keep producing power.

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