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CO: Green vs. green: Trees cut down to make way for solar

By   /   August 4, 2012  /   News  /   16 Comments

By Todd Shepherd | Colorado Watchdog

DENVER — The Denver Housing Authority is installing dozens upon dozens of solar panels on the Quigg Newton subsidized housing project near I-70 and Pecos. But as the solar panels go up, trees are coming down to accommodate them — a move that could ultimately raise the energy needs of at least some of the housing units.

A tree is marked for trimming or removal to make room for a solar project.

It’s a battle between new green technologies and the oldest of green technologies.

“For optimal solar power production, it was determined that between 100-120 trees may be trimmed or removed for the total DHA solar project, which includes 668 solar electric systems on 387 DHA resident buildings,” DHA Community Affairs Officer Stella Madrid wrote in an email. “As DHA continues to assess the need for trimming and removal of trees at each of the solar installation, we will utilize the ‘Right Tree, Right Place, Right Way’ approach to minimize the removal of trees and maximize the solar panels.”

But this 1997 scientific study from the Lawrence Berkley National Laboratory found that trees providing direct shade to a home can save 30 percent seasonally on energy costs related to heating and cooling. A more recent study, as pointed out by a commenter on this story, estimates the summertime energy savings at about 5 percent. Either way, it seems safe to conclude that removal of trees and tree limbs at the sites of the solar panel installations may actually increase overall energy consumption.

The DHA’s Madrid acknowledges the tree removal and trimming comes with an impact.

“While there may be some impact to some units,” she wrote, “there are instances where there is zero impact (building facing north). Other building impact mitigation includes: (a) the units have insulated thermal-pane windows to reduce seasonal thermal transfer; (b) building insulation upgrade from R-19 to R-49; (c) Resident responsibility and resident education is ongoing to realize efficiency in heating and cooling. This includes promoting window shading to minimize or realize solar gain from direct sun light.”

One of the reasons deciduous trees are so efficient at providing year-round energy savings is because the shade in the summer obviously reduces the overall heat on the building, thereby reducing air conditioning needs. But as the seasons change and the leaves fall off, more sunlight is then allowed to filter in and warm the building during the colder fall and winter months.

There isn’t much middle ground between the choice of a shade tree that comes into contact with a solar installation. DHA notes that even a small amount of shade can greatly reduce the efficiency of a solar panel, and not just because the amount of available sunlight is reduced. Shade trees can cause parts of a solar panel to over-exert — a phenomenon called “hot spot damage” — which can then cause the panels to overheat or even burn out.

This tree at a housing complex is marked for removal or trimming as part of a program to bring solar power to the neighborhood.

The Colorado Watchdog investigation began when residents said trees were being marked for removal. When asked if the markings indeed meant the trees would be removed, the agency gave an Orwellian response: Yes. And no. And maybe. “The designated markings indicate assessment for three action options,” Madrid wrote.”(1) tree trimming needed only;  (2)  no action needed; or (3) removal necessary to optimize solar panels.”

Not surprisingly, this isn’t the first time a tree-vs.-solar contest has emerged. As this Washington Post story details, the removal of shade trees to accommodate solar installations caused significant controversy in Takoma Park, Md., including disputes about city fines for tree removal. The Post called it a battle between “sun worshipers and tree huggers.”

DHA told Colorado Watchdog that the agency will plant “solar-friendly” trees this fall.

Hannah Glennon contributed to this report.


Todd formerly served as staff reporter for Watchdog.org.

  • Regan

    I like the picture in this article… behind the tree with the giant red X is a unit with a window air conditioner hanging out of it. Would that be a unit with one of those: “insulated thermal-pane windows to reduce seasonal thermal transfer”. This stuff is such a farce!! So they’re gonna put solar panels, air conditioning units AND thermal pane windows in? Uh huh, whatev.

  • wood chuck

    Like palms trees

  • Kill the shade trees to install solar that will probably not cover the increase use of energy it may now take to cool off the buildings. How progressive.

  • pete

    The Colorado watchdog needs to reread the study. The finding was that shade trees
    yielded “seasonal cooling energy savings of 30 percent.” That is to say, during
    the summer, the amount of energy used to cool the house was reduced by 30
    percent. Far different from the Colorado Watchdog’s assertion that the study
    found the trees deliver “30 percent annually on energy costs related to heating
    and cooling.”

  • pete

    By the way, since that tiny study in 1997 (on two
    houses!) erroneously cited by Colorado Watchdog, there has been a much larger study done. In fact, the more recent
    study is described by the National Institute of Standards and Technology as “The first large-scale study of
    its kind.” It found “Trees positioned to shade the west and south sides of a
    house may decrease summertime electric bills by 5 percent on average.” They also found that north-side trees actually increase the amount of energy required to cool the house.
    Source: http://www.nist.gov/el/shade_050509.cfm

  • pete

    On a sunny day, a typical 4-kilowatt residential solar power system will produce in 1-2 hours the daily level of summertime shading-effect savings (3.6-4.8 kWh) detailed in the study cited.

  • Mike W

    You seem to have some knowledge of this. My question would be how will the panels be functioning after 10 then 20 years of use. I seem to remember they will become less effective unless there is frequent regular cleaning or other maintenance and even with proper care will lose

    efficiency over time most requiring replacement at about 20 years. That equation should be added into the analysis along with the initial effects of tree cutting. My guess is the the tree benefit will remain constant over the years. (tree maintenance being also required).

  • Pete, thanks for pointing out the more recent study, which I’ve added to the post. After doing about 30-some-odd searches, I simply never came across that article. “Annually” has been changed to “seasonally” as well.

  • Pete

    Panels lose about 1/2 percent efficiency per year. Systems today are warrantied for 25 years, generally. They will be less efficient as they get older but no need to replace.

  • Pete

    Props to you for the changes. Trees = good, and summer shade in the right places = good. A good solar installer will work around as much shade as possible. Also, microinverters proving to be helpful in minimizing shade impact on PV system performance. NREL:

  • Cassy

    Trees do much more than simply save energy by providing shade. They cool and humidify the surrounding environment through evapo-transpiration, much like a swamp cooler. They produce oxygen. And let’s not forget, they beautify the environment! The DHA is doing much more harm than good here.

  • Wonder if anyone will be inspired to write a poem about the rack of solar panels?

  • Sneezer142

    Solar panels typically take years and years to pay for themselves in energy savings, but some of the housing projects on which they are being installed may not be around long enough to generate these savings, judging from the photo. One avenue of potential follow-up might be exploring whether the buildings on which these units are being installed will be around long enough that this even makes sense. Not that this will matter much to those pushing the solar agenda, who routinely choose symbolism over substance.

  • Dano2

    There are several studies out of the Center for Urban Forest Research in Sacramento that quantify benefits of trees wrt energy consumption that conflict with the Donovan and Butry. Trees on the north side of a house attenuate airflow, lessening envelope air loss. I just so happen to have finished a presentation a few hours ago using a diagram that showed benefits of trees by position, and none of the cases had a negative on the north side. Work by Sarkovich of Sacramento Tree Foundation.



  • Dano,

    Thanks for contributing to the discussion!


  • Gov. Christie signed a solar bill that will help destroy more than just one tree but many a forrest http://www.trentonian.com/article/20120724/FINANCE01/120729838/nj-gov-christie-signs-solar-subsidy-bill