Be-aware of the Dark Side of Trees
University of Denver Sturm College of Law
Legal Research Paper Series
Working Paper No. 12-08
KK DuVivier
author of The Renewable Energy Reader
(http://www.RenewableEnergyReader.com)
University of Denver - Sturm College of Law
Everyone loves puppies, and everyone loves trees. But just as we had to learn to curb and clean up after our dogs, we now need to learn to become responsible tree owners.
Many of today’s well-intentioned tree-planting programs ignore the dark side of trees that threaten green energy solutions such as urban gardens, buildings with passive solar designs, solar hot water, and solar- generated electricity systems.
A winter limb shadow from a deciduous tree can reduce electricity production from a standard crystalline silica photovoltaic panel thirty-fold according to a 2009 study by the National Renewable Energy Laboratory. Over the course of a year, a tree shading the roof of a house can cause the loss of ten times the electricity generation it might save in air conditioning. Many tree varieties promoted by planting programs mature at heights that can interfere with green energy systems two and three lots to the north.
Be aware of the dark side of any tree you plant—both the planting location and the shade footprint. Otherwise, any carbon-capture gains from the new trees may be offset by the increased fossil-fuel burned to replace the clean solar energy lost.
Summary of Energy-wise Urban Tree-Planting Guidelines
Pay attention to every planted tree’s shade footprint.
Even deciduous trees can block critical sun in the winter, so avoid planting any trees close to the south side of your house.
For trees to the north of your lot, show consideration for how your tree’s mature shade footprint will impact your north neighbors’ green energy options.
Taller maturing trees need much more setback to avoid negatively impacting lots to the north. (A tree that matures at 20 feet should be set back 40 feet from the property line, & a tree that matures at 50 feet will need at least an 80-foot setback. Many urban lots are only 50 feet wide in the N-S axis.)
Text by Professor K.K. DuVivier, University of Denver, author of The Renewable Energy Reader (http://www.RenewableEnergyReader.com). All graphics are illustrations by Dava Lurie from Martin Jaffe & Duncan Erley, Protecting Solar Access for Residential Development, U.S. Department of Housing (1979) or Duncan Erley & Martin Jaffe, Site Planning for Solar Access, U.S. Department of Housing (1979).
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