Equinox	Summer solstice	Winter solstice
	90	113.5	66.5
Your latitude	-(    )	-(    )	-(    )
Sun angle	(    )	(    )	(    )

	Equinox	Summer solstice	Winter solstice
	90	113.5	66.5
Your latitude	-37	-37	-37
Sun angle	53	76.5	29.5

At a latitude of 37 degrees, the noonday sun at the beginning of winter is about 30 degrees above horizontal.  This is the sun’s lowest point in the sky; in spring, fall and summer, it is much higher.  But, since this is when we need the sun’s heat the most, we use 30 degrees to find out whether anything blocks the sun from lighting the greenhouse when it is needed.  Trees, even with their leaves gone, can block a large portion of the sun.  Other buildings, hills, etc. need to be sited in such a way that you know they don’t shade needed sun from the greenhouse.

Ninety percent of all usable sunlight occurs between the hours of 9:00 AM and 3:00 PM.  To be precise, this is solar time.  If solar noon is at 12:45 PM in your location, then the above should read “9:45 AM and 3:45 PM.”  You should also be sure to take Daylight Savings Time into account when figuring out solar noon.

When figuring out what may or may not block access to the sun, remember that the sun rises low in the east, sets low in the west, and is at its high point only at noon.  So a chart showing solar obstructions will be in the shape of an arc.

While the sun may shine over the tree in the above drawing at noon, the same tree the same distance away in the east or west, might shade the sun.  To avoid grief, before locating the greenhouse, you must consider these points of solar access.

To read more about building a greenhouse add-on for less than $15 per square foot, download the 99 cent ebook Low-Cost Sunroom.

This post is part of our Low-Cost Sunroom lunchtime series.  Read all of the entries: Low-Cost Sunroom Solar greenhouses Solar orientation of a greenhouse Solar access Heat retention in a greenhouse

Want more in-depth information? Browse through our books.

Or explore more posts by date or by subject.

About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.



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