We get a lot of questions about how the exact location for the “PG&E Solar Schools program Solar on a Stick” gets selected. The story about how the spot was picked at the Presidio Middle School in San Francisco (right on the north side of Geary) illustrates how this process is a little bit science and a little bit math with some important diplomatic negotiations thrown in.

Science: The solar panels are installed at the top of a pole and angled toward the sun. They have to face south and there should be nothing shading the panels. All of the PG&E Solar Schools projects are installed as close to the same conditions as possible to make sure that schools are able to compare/contrast solar systems with location and weather as the dynamic variables affecting performance. What is under the panels and around the base of the pole doesn’t really matter much, but we never want anything between the panels and the sun. There are normally a lot of areas available at schools that work well for the installation, but urban schools can present a bit more of a challenge. We don’t want to impact playground space and need to work around existing structures. We use a device called a Solmetric SunEye that measures the path of the sun and basically tells us whether or not each location is good, bad, or in between. I have to tell you that Alyssa usually does this so I am going to let her explain the devices that she uses to “test the sun.”

Thanks Glen. In the past, we used a device called a Solar Pathfinder, which has been around since the 70’s and still works well. Many get a chuckle out of the fact that I refer to the 70’s pathfinder device as “old school” but still good! In fact, we often start with this device as the lower tech (but still accurate) tool.

We walk around the school campus, and discuss which areas:

1. Are preferred by the administration (this is where the diplomatic negotiations start - everybody has a different opinion, and we need consensus before we can move forward),
2. Are relatively unobstructed by trees or structure shade and “safe” from flying objects (other than the sun’s rays),
3. Are relatively close to where we need to connect the system to a panel to feed the clean solar power into the classrooms.

We triangulate between these three necessary inputs, and take measurements at each site. When we get close to one or two potential locations, we take measurements with a Solmetric SunEye - this is the high-tech updated tool. Below is a sample of an image taken from Presidio Middle School. The lines represent hours of the day and months of the year - this site, as you can see, is pretty darn close to perfect! But the story doesn’t end here.

Math: We have to make sure that the installation is not too far from the electrical box where we connect the solar array with the PG&E electricity grid, and that the numbers work (see the Solmetric chart above). It is expensive and disruptive to run wires underneath asphalt and concrete, and even to trench in a grass yard. There can be some loss of electricity when the wire carrying the solar energy has to travel a long distance. Some of the “solar on sticks” had to be put pretty far from buildings just because of shading and other issues, but we try and measure the distance between the site where the pole might go, where the PG&E service comes in, and where our closest electrical subpanel is located. We also can’t be within 10 feet of a retaining wall or structure because of code restrictions. We weight all of the necessary inputs, and then talk as a group about the preferred location. As you can guess, not all of the inputs can be quantified - future plans for the site, personal opinions on aesthetics (including those of neighbors), and other topics come in to the discussion.

Compromise: Finally, we have to take the school’s staff and students and activities into consideration. We won’t put the panels in front of a walkway so the students would have to walk around it, and we don’t want to put the pole in the middle of a baseball field or soccer field or basketball court. We need to keep the fire lanes clear. Our favorite spots are unobstructed spots in the front of a school or near the science classrooms so that the students can see the solar panels everytime they walk in or from their desks in the science wing where they might be looking at the online data monitoring site. Ultimately, there are often non scientific and non mathematical compromises that determine the final location. And this is where we get back to Presidio Middle School, and finish our story about X marking a spot.

The Presidio Middle School is a huge and beautiful historic looking building built in 1930 that sits off of Geary Street in San Francisco. There is a wonderful gymnasium and expansive playground. The walls and roof remind you how we used to build schools a very long time ago- we built them to stand for a long time, and the artistry of the day was included in the building lines. I love the look of that school.

When we first visited the school we met with school administrators and we selected a spot for the pole based on a number of the factors that I talked about above. The location was good and everyone present agreed to it. But then Alyssa got an update from Assistant Principal John Greener. He said the woman in charge of physical education opposed the spot for the solar on a stick installation. She had plans for a long jump track in that area and the pole would interfere with her plans. She had not been at the original meeting, but she was now voicing her opposition to the area of the playground where we were about to do the installation.

So Alyssa and I met John Greener at the school office and he called several of the science teachers and the PE teacher to the playground. Alyssa and I walked around and Alyssa used her device to make a mental note of the locations where the pole could go and then we all met in a group discussion in the middle of the playground. We talked about the science issues and the math issues and then we got around to the location we had chosen originally. The first location seemed impossible, but an interesting thing happened. The PE teacher started asking about all of the various locations where the pole could go and a funny thing happened. She made a suggestion for a location and we all looked at it and everyone nodded, “that works.” It was in fact a better location from a science perspective.

For me, the spot did not look like it would be acceptable to the woman in charge of the playgrounds because it was in the middle of the playground. But what none of us had realized was that the location she offered to us was in between a number of play areas. While it is centrally located, it does not interfere with any individual play area. We had all tried to find a location that was a little “out of the way” of the play areas and she had come back with a much better location for us that is in the middle of the entire playground and very visible to traffic on Geary. We could not have picked a better location. (I did ask everyone from John Greener to science teachers to the PE teacher to Alyssa to point to the spot so that we had evidence that this was in fact the location, but I did it more for fun than to resolve any future disputes. The fight was over and the compromise worked out so much better for the project than any of our original choices. The day Alyssa and I drove to the school it sounded like a fight was brewing, but in the end everyone was laughing and happy. Science and math had won a victory…on the playground.

This entry was posted on Thursday, February 21st, 2008 at 4:52 pm and is filed under California, Perspectives, Solar Schools . You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.