Calculating shade distance

If you have a brick wall that you have trained fruit trees against and you want to build another wall that is parallel to the first to have more space for fruit trees, how would you calculate the distance you need between the two walls so they don’t shade each other?

Generically speaking the average angle of elevation will be 90 degrees - your latitude. But there is a +/- 23 degree variation over the course of the year.

So if your latitude is 35 degrees north, then the angle of the sun will vary between a low of 32 degrees on the winter solstice up to 78 degrees on the summer solstice.

To make sure the southward wall doesn't shade out the northern wall, you'd have to do a little trigonometry. Take the height of the south wall, h, and apply the tangent.

To keep the north wall shade free all year long, we would use the winter solstice angle.

Distance between walls > h / Tan( 32 )

You can adjust this formula to different angles if you are only concerned about sun from during the warm parts of the year by using higher angles. Equinox to equinox would use an angle of 55 degrees in this example.

Hope that helps!

tamo42 wrote:
Generically speaking the average angle of elevation will be 90 degrees - your latitude. But there is a +/- 23 degree variation over the course of the year.

So if your latitude is 35 degrees north, then the angle of the sun will vary between a low of 32 degrees on the winter solstice up to 78 degrees on the summer solstice.

To make sure the southward wall doesn't shade out the northern wall, you'd have to do a little trigonometry. Take the height of the south wall, h, and apply the tangent.

To keep the north wall shade free all year long, we would use the winter solstice angle.

Distance between walls > h / Tan( 32 )

You can adjust this formula to different angles if you are only concerned about sun from during the warm parts of the year by using higher angles. Equinox to equinox would use an angle of 55 degrees in this example.

Hope that helps!

I got the same information from another source, but I think you have explained it better.  I knew trig would be involved and I knew I would have to calculate the shadows on the shortest day of the year to find the longest possible shadow.  My other source didn’t specify this.

There are sundial calculating programs on the web for free.  I don't seem to have one installed on this computer and can't remember the name of the one I used.

Might try sketchup (free from google)

It's a 3d building modeling program that has fairly accurate shadows (set your lat, long first).

Used it awhile back to test some building ideas and see how the shadows fell. Can also scrub through the months to check them through out the years.

http://www.architectionary.com/TutorialsShadows

Keep in mind that you don't have to get light to the very bottom of the tree since you don't want to leave branches on the ground.

ape99 wrote:
Might try sketchup (free from google)

Bookmarked it now. Thanks.

You can bunch them slightly closer than that even.  You don't need light on the trees when there are no leaves.  Right about now the sun is half way from the winter solstice to the vernal equinox.  If you're at 35° latitude, the sun's altitude at noon is 44° above the horizon.  So if you had the wall as far from the base of the tree as it is high, it'd probably be good enough. 

I'm closer to 45° north, so I'd need the distance to the wall to be about 1 1/2 times it's height.

Dan

Solid point, you only need to have the sun where you want it when the leaves are out. So first figure out how you want to prune the trees, then figure out when they will have leaves on them, then figure out how far down the sun will be during the time it does you any good.

I'm at 61°, I would have to build the wall down the block aways.

Hey guys I hate to rain on your parade but you must have sunlight on the ground around the tree. Soil temp helps determine when the tree buds in the spring. You may push the budding time by weeks or more, shorting your growing season. I live in a frost pocket (no direct sunlight in winter) so I know of what I speak.

sad day.

Emerson White wrote:
sad day.

Care to explain that, Emerson?

Depends on what climate you're in.

Do what they did in europe (forget the country)...set up a huge mirror array to bounce sunlight to a severely winter shaded town in the mountains.

gorilla.gardening wrote:
Hey guys I hate to rain on your parade but you must have sunlight on the ground around the tree. Soil temp helps determine when the tree buds in the spring. You may push the budding time by weeks or more, shorting your growing season. I live in a frost pocket (no direct sunlight in winter) so I know of what I speak.