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Passive Sun & Shade Harvesting

Passive sun & shade harvesting systems do not require manufactured systems that generate or distribute energy in order to operate. They are silent – no humming appliances or equipment. They tend to be simple, working with what is already freely at hand. They can be designed or made in a way that they are not dependent upon imported resources or materials. Passive systems can be understood, collaborated with, designed, and/or maintained by the average child or adult. For how to do so, see chapter 4 and appendices 7 and 8 in Rainwater Harvesting for Drylands and Beyond Volume 1, 3rd Edition.

Planting for winter cold and warmth needs. A cold-sensitive evergreen citrus tree on the warm winter-sun side of house, and a cold-needy winter deciduous fruit tree (that needs enough winter chill hours to prompt spring/summer flower budding) on the winter-shade side of house. Note: Citrus tree is placed so it will not shade winter-sun-facing windows of house in winter (so windows can heat and light the home for free). To figure out such correct sun & shade harvesting spacing for where you are, see the winter-solstice shadow ratio and other strategies for your latitude in chapter 4 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition. Illustration by Joe Marshall.

The best passive systems are alive. They grow and get better with time; generate additional resources/potential like food, fertility, and joy; and they sequester carbon while cleaning our water and air (which they also produce). An example is a “solar arc” of trees planted on the east, west, and winter-shade-side of buildings, gardens, livestock pens, and gathering areas—while no trees shade out access to the winter sun on the winter-sun-side in the direction of the Equator (the winter-sun/Equator-facing-side is the south side in the northern hemisphere, or the north side in the southern hemisphere).

A solar arc of trees shades out the hot summer rising and setting sun for free cooling, while allowing for full winter sun access and free heating and lighting (see illustration below). The trees also cool the area in summer with the evaporation of moisture transpiring from their leaves, and they can further warm us in winter by deflecting winds. The trees and their understory plantings can be freely irrigated with the roof runoff, greywater, and other free on-site waters harvested from the building the trees shelter.

Studies have found this solar arc strategy results in over a 50% energy savings when compared to a similar building without such shade trees.

Solar arc of trees and resulting seasonal shadows and sun exposure on an east-west oriented building at 32˚ N latitude.
View of building’s winter-sun side. Roof-mounted solar panels and solar water heater receive full sun all year round. Winter-deciduous trees (lighter green) on the east and west sides of building expose it to more winter morning and afternoon heat and light than evergreens would.
For video of this on winter solstice see here
For video of this on summer solstice see here

Summer-cooling and winter-heating solar arc of trees – overhead view.
No major trees are planted on the winter-sun-side of building to retain winter solar gain for winter-sun facing windows, solar panels, and solar hot water heater. Though you can finesse this, by selecting and placing vegetation whose mature heights won’t block desired winter sun access—see the “winter solstice shadow ratio in chapter 4 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition for more details.
Winter-deciduous trees (lighter green) planted on the east and west sides of building shade out rising and setting sun in hot months, while letting in some light and heat in winter. Evergreen trees (darker green) planted on winter-shade-side of house (north-facing in northern hemisphere, south-facing in southern hemisphere) further shade home from rising and setting summer sun. In more urban settings with less open space, vines and trellises, and other buildings, along with trees can act as aspects of the solar arc. See chapter 4 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition for how to best create such a solar arc for your site.
Illustration by Joe Marshall.

Some other passive sun & shade harvesting systems include:

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on how to design and implement passive sun & shade harvesting strategies at all latitudes, and irrigate the living ones with free on-site water sources…

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Book Cover #1

Volume 1

Volume 1 has detailed sun & shade harvesting info on:

  • Orienting buildings and landscapes to the sun
  • Designing roof overhangs and awnings to optimize winter sun and summer shade
  • How to choose and size windows to optimize passive heating and cooling
  • Solar arcs
  • Sun & shade traps
  • Maintaining winter sun access with winter-solstice shadow ratios and solar rights
  • Sun angles and path for any latitude and season
  • How to find your way, and true north or south, with the sun and other stars
  • How to place vegetation or structures to maximize natural ventilation or windbreaks
  • Table comparing the energy consumed, water consumed, and carbon emitted of active and passive clothes drying, water heating, food storage & prep, lighting, heating, and cooling strategies.
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