Sun & shade harvesting is designing, building, planting, & playing with the seasonally changing path of the sun—and various life forms’ response to this—to both maximize free, passive summer shading/cooling; and free, passive winter heating/lighting of our buildings, gathering areas, and growing areas in a way that maximizes our individual, community, and planetary comfort, health, and resiliency so that we save and enhance resources like time, money, water, and air by maximizing potential for all.
The first step is to observe and become aware of how the sun’s path across the sky changes with the seasons where you live. Where does the sun rise and set throughout the year, and how does its midday height/angle above the horizon change?
LEFT: The winter solstice path of the sun at 32˚ N latitude. House and roof overhang shadow cast at noon. Dotted shading represents section of the sky the sun does NOT traverse.
RIGHT: The summer solstice path of the sun at 32˚ N latitude. House and roof overhang shadow cast at noon. Note how things differ from the winter-solstice sun path illustration.
See appendix 7 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition for images of the sun’s path at other latitudes and
LEFT: The winter solstice path of the sun at 32˚ N latitude. House and roof overhang shadow cast at noon. Dotted shading represents section of the sky the sun does NOT traverse. RIGHT: The summer solstice path of the sun at 32˚ N latitude. House and roof overhang shadow cast at noon. Note how things differ from the winter-solstice sun path illustration. See appendix 7 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition for images of the sun’s path at other latitudes and seasons.
The key to sun & shade harvesting is that you harvest BOTH the sun AND shade in different seasons in a way that enhances life and conditions in ALL seasons, but at the expense of NONE.
Drawing of sculpture showing the seasonally-changing angle and harvest of sun and shade at my garottage (one-car garage turned cottage) in Tucson, Arizona. Sports of season represent the sun angle and line of the shadow cast at noon by roof overhang and gutter on the winter solstice (ski pole), spring/fall equinoxes (golf clubs), and summer solstice (fishing pole). We let in the sun when we need it, and shade it out when we don’t. Shadow cast here is on spring equinox. We designed the roof overhang length and height in relation to the winter-sun/Equator-facing windows to maximize winter sun access and summer shading.In a colder climate than Tucson’s, all would be designed to let in more sun in the spring and fall, while in a hotter climate than Tucson’s all would be designed to shade out more of the sun in spring, fall, and perhaps even winter. Reprinted from Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition.Harvesting winter sun. Winter-sun/Equator-facing side of house at noon on the winter solstice.Roof overhang and awning designed to maximize the passive harvest of winter sun, heat, and light. Awning is retracted for the cold/cool months.Solar oven (on round table) uses the sun to passively cook food. Compare to summer shade harvest below.Harvesting summer shade. Winter-sun/Equator-facing side of house at noon on the summer solstice.Roof overhang and awning designed to maximize the passive harvest of summer shade and cooling. Awning is extended for the hot months.Solar oven (on round table) uses the sun to passively cook food. Jar on table uses the sun to passively brew sun tea. See Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition for how to design you space to harvest BOTH summer shade AND winter sun.
What sun & shade harvesting is NOT is harvesting sun to heat, light, and power us winter, but in a way that then overheats us in summer. Or harvesting shade in summer in such a way that it unfortunately also shades and colds us in winter.
Bad example of sun & shade harvesting. Solar rights/access denied. The homes have been placed so close together they shade out their neighbors’ access to the winter sun. Photo taken in winter. Tucson, Arizona. South, and the winter sun, is to the right side of the photo. Fronts of homes face west. House on right shades first floor windows of neighbor’s house that would otherwise access winter sun for free heat and light. Two-story house shades out entire winter-sun-facing side of northern neighbor’s including their solar water heater (on roof)—thereby turning a “sustainable” solar hot water heater into an unsustainable, non-functioning appliance in winter. This development markets its homes as energy efficient with active sun-harvesting photovoltaic panels and solar water heaters, but it is nowhere near as efficient as it could’ve been had it also incorporated/integrated passive sun & shade harvesting strategies, such as maintaining full winter sun access for all homes. See the Winter-Solstice Shadow Ratio for your latitude in Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition to maintain winter sun access on your site (and for your neighbors). Photo: Brad Lancaster
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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.
