Solar Access and Shading

December 14, 2010

Another good resource we learned about is the Tools Lending Library at Pacific Energy Center.  This is another free program provided by our local utility, PG&E.  Just as you would borrow books from the public library, we filled out the online request form to borrow tools from PG&E’s tools library.  Nice, isn’t?

Since we needed to get “shading analysis” for the 4 sides of the house to be used for the passive house calculation we looked for “Shading/Solar Access” types of tools in the lending library.  The search returned 7 results and we selected to borrow the SunEye by Solmetric. 

The SunEye comes with the hand-held electronic device, power cable, USB cable, PC (not Mac) software and a manual in the case. We also borrowed a Windows PC from Kurt’s brother because the companion software only runs on Windows machine and not on Macintosh — we only have Macs at home.  It took us a few tries to get the picture and the data in the form that was useful for our passive house consultant, Graham.  We found the user interface of the tool to be good once you get the hang of it by taking a few pictures.  I think the hardest part of the data transfer to the PC was getting the cable to plugged in correctly to the hand held device.  The hand-held side of the USB cable did not have an obvious “this way up” marker so you could easily plug it in the wrong way.  Once the data was transferred from the hand held to the PC a report can be generated and extracted for emailing.

Since the data from this tool is most often used for determining the optimal placement for solar panels the instructions in the manual directs the user to be facing south when taking pictures.  We actually had to stand with our backs to the wall to get the pictures we wanted.  Here’s what we did to take the pictures at each of the sides of the house:
1.  After powering on the device, press the sun icon on the lower left hand corner
2.  Press Session button and choose New in the selection window
3.  Enter data such as the session name, notes and location information
4.  Press sun icon
5.  Press Skyline then choose New in the selection window
6.  Enter panel tilt (we entered 25 degrees) and press OK
7.  Then, standing with our back to the wall, we looked in the camera image on the screen to make sure that the sun path clears the roof overhang and stood very still to make sure that the camera was level (using the built in level) and pressed snap to take the picture.

Starting at the south (back) side of the house we took the snaps.  Each time I ducked away from the fish-eye lense to make sure I was not in the picture.  We repeated steps 4 – 7 for each side of the house.  This is what the pictures looked like:

East side of the house shows lots of shading (in green) from trees.  Yellow color represents sun.

South side of the house receives lots of sun.

After Kurt took the pictures he stood still while I measured the distance from the wall to the fish-eye lens.  We took 2 pictures on the west and north sides of the house because they have protrusions. (e.g. the porch sticks out from the front of the house)  Here are the measurements:
South:  49 inches
West 1:  42 inches
West 2:  60 inches
North 1: 52 inches
North 2: 50 inches (from the bottom step of the porch)
East: 52 inches

We used the post-processing software to correct the tilt angle to 90 degrees to reflect the shading to the vertical walls.