Can I shade my home with trees without blocking my solar panels?


Can I shade my home with trees without blocking my solar panels?

Asked by DeeDee, Fresno, Calif

I am trying to find information and/or tools to help me figure out where to plant trees for shade while not interfering with the effectiveness of my roof solar tiles. My new home will be south-facing in the front, while the open side (corner lot) will be to the west. I need to determine what kinds of shade trees to plant and where to plant them, to be sure they are neither too tall nor in the wrong place(s). Could you help me with this paradox?

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Mick Dalrymple's picture

Coincidentally, I am experiencing your exact situation right now. After four years of our south-facing front yard serving as a neighborhood eyesore while we slowly killed our water-glutton bermuda grass, we are finally just finishing Phase 1 of our new landscape. The west-facing side yard is next. One of my primary concerns has been how to create shade without casting shadows across our flat-roof-mounted solar PV array and solar water heater panel. While it took some basic geometry and plant research and will take a couple of years for the landscape to mature, I believe we are headed for success.

Firstly, the photovoltaics should go on the south-facing roof. It sounds like your solar will be amorphous PV roof shingles rather than panels, so the angle at which they will accept and convert light is wider than polycrystalline panels, but their productivity will still be much greater on the south side than on the west.

Secondly, if you can utilize front porch roof structures, pergolas, arbors, awnings or other horizontal measures for shade on the front, utilize them to shade the front windows, walls and door in the summer while allowing winter sun to hit these surfaces and naturally warm the home. This will also give you more margin for error if you also want to use trees in front.

Thirdly, use native or climate-adapted, low-water-use deciduous trees for the same purpose. By dropping leaves in the winter, you let more sun in to warm the home. Try finding a local low-water-use plant and tree resource guide from an agricultural cooperative extension service (generally associated with land grant universities), or your water utility. These guides will also often list the mature height and diameter of the trees and plants.

Fourthly, on the west side, use vertical shading. This can take the form of trellises and vines on the wall, screen walls, roll-up or permanent shade screens on the windows, shrub-like plants and trees, or even radiant-barrier paint. The key is to stop the low-angle, late-afternoon sun from reaching the wall and windows, rather than relying on insulation or interior shades to mitigate its effects. Again, something that ?goes away? (deciduous plants) or that can be removed easily in winter is better. As far as height of trees, stick with a tree or shrub that isn?t going to get higher, or much higher, than the south-facing roof line. The situation is very different from shade from the south in that misplaced shade from the west will shorten the productivity window of your shingles each day (mainly in the afternoon when you want the most productivity), whereas shade from the south will dramatically reduce the productivity all day long.

Now, for front-yard tree selection and placement, you can either eyeball the geometry or do a bit of drawing on an elevation plan of your home, depending upon your level of comfort and the margin for error. Your latitude is 36.75 degrees north, which determines the ideal angle of solar panels to the sun, but the angle of the shingles is what it is. Determine the angle of your roof pitch on your south-facing roof. Draw an imaginary (or real line on the plans) perpendicular to the bottom edge of the bottom row of PV shingles. If you are not sure where the shingles will be located on your roof, play it safe and use the lower edge of the roof line. Extend the line up and out into the air above the yard. No tree in the yard should cross over the line when it is at mature height and spread. If you want taller trees, place them farther toward the street. If you have limited distance to the street, use smaller trees. Leave a safe margin because sizes in landscape guides are approximate averages and the productivity penalty for shading the panels is large and will hit you in the pocketbook.

While you are looking at landscaping, consider rainwater capture and bioswales to keep water on your homesite and use it for the trees and other vegetation.

Being in the arid Southwest, we wanted to use some Velvetina mesquite trees to create a nice canopy of shade in the front and actually harvest the mesquite beans (whose flour makes some of the best pancakes I have ever had!), but the trees grow taller than I was comfortable with, given the compactedness of our front yard. We found some very low-water-use trees that look similar and grow fast but only reach 15 feet high. On the west side, we are going to build a ramada against the house this winter, topped horizontally with wired-together ocotillo stalks to let in filtered light. Then, we are going to plant dense, tall shrubs on the outer western edge of the ramada for vertical shading, creating an outdoor ?room? that should be pleasant to use for several months of the year and that will act as a micro-climate thermal buffer for the hot months (which seem to be getting more and more numerous!).

Congratulations on your new home and renewable energy! I hope your landscaping completes your home nicely.