Doug Kerr, "Dougtone" via flickr
SACRAMENTO, Calif. — When California shut down nuclear power plants in 1989, it lost half its electrical capacity overnight, says Misha Sarkovich, program manager at the Sacramento Municipal Utility District.
"We began to aggressively invest in conservation programs," Sarkovich says. "One of the first programs where we thought outside of the box was the shade tree program."
It turns out that trees are the answer.
Since 1990, SMUD has planted more than half a million trees to reduce energy costs — including trees at about 175,000 single-family homes. Strategically locating trees can save money, and with spring and tree-planting season beginning, people can make a modest investment that can improve the bottom line.
Greg McPherson, research forester at the Pacific Southwest Research Station in Albany, Calif., says trees have many benefits, but are most helpful for heating and cooling homes.
An analysis by McPherson in The Electricity Journal in 1993 showed that using three 25-foot-tall trees (two on the west and one on the east) on a two-story structure gave a yearly heating and cooling energy savings ranging from 2 percent to 9 percent. The warmer the climate, the better the savings.
A 2008 study at Auburn University found that electricity consumption and costs are 11.4 percent less during the summer when a house has just 17.5 percent heavy shade coverage, compared to a house with no shade.
The Auburn study also found (using rates at the time in Auburn, Ala.) the 11.4 percent energy savings would equal $31 to $33 per month. Even light shade, if it covered about half of a house, saved 10.3 percent on cooling costs.
The savings do not just come from shading, but also from "evapotranspiration," the transfer of water vapor from plants to the air around them — essentially acting like evaporative coolers. Trees also break up the flow of wind, slowing it down.
Other benefits are reduced water run-off. In 2008, the Indiana Department of Natural Resources commissioned a study that looked at the various benefits of trees. The study found that 31 percent of the value of planting trees for the community at large was slowing the runoff of storm water. Slowing runoff reduces water treatment costs and reduces soil erosion.
Twelve percent of the benefits was reducing energy consumption. More than half of the benefits were aesthetic and other benefits, the study said.
To a lesser extent, trees also improved air quality (4 percent of the total benefit) and CO2 absorption (1 percent). They clean the air by absorbing gaseous pollution into their leaves and by trapping particulate pollution.
Sarkovich says trees are also good for taking CO2 out of the air, which would probably double the cost effectiveness of planting trees, he says. The ecosmartlandscapes.org website helps people calculate the ecological impact of their trees and plants.
People can search at energysavingtrees.arborday.org for more information about saving money with trees and to see if their local utility provides free shade trees. Utilities in seven states plus Washington, D.C., are partners with the Arbor Day Foundation. Other communities may also have information and programs.
The SMUD's shade tree program (which provides free trees to customers in the Sacramento area) has saved an average of $12 per year for each mature tree. "We think a combination of strategically planted trees cans save up to $40 of cooling costs, if done right," Sarkovich says.
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