From pv magazine USA
Is it okay to cut down a tree in order to install solar panels? This complex question must consider emissions, as well as the continuity and value of nature.
An analysis by the European Environmental Commission suggests that a single tree will sequester 22 kg (48.5 lbs) of carbon per year in its physical structure, until the 3 trillion trees die and release themselves as methane. Each acre of mature forest is inhabited by 100 to 400 trees, sequestering 4,850 to 19,400 pounds of carbon per acre each year.
Keep in mind, those carbon sequestration rates only apply to full-bodied, mature trees. Brush trees and saplings capture only a fraction of the volume of carbon of large mature trees, which is an important factor to consider when deciding whether or not to fell trees.
When we look at the emissions offsets produced by solar installations, the numbers depend on differences in how each region’s electricity is generated, as well as the time of day that region’s electricity is generated. The hydroelectric power that supplies the majority of upstate New York’s electricity is considerably cleaner than the coal plants that supply roughly half of the electricity to Nebraska, and therefore solar installations in Nebraska offset many times more emissions than equivalent installations located in upstate New York.
According to the US Department of Energy’s Energy Information Administration, the nation averaged 0.85 pounds of carbon dioxide emissions per kilowatt-hour generated. Thus, an average 400 W solar panel generating 1.5 kWh per watt per year* will offset 510 pounds of carbon dioxide emissions.
*Solar panel output varies greatly by geographic region – panels installed in the south generate more electricity than those in the North.
A single solar panel offsets a carbon emissions equivalent exceeding that of ten mature trees. The average residential solar installation, roughly 7,000 watts, offsets the emissions equivalent of more than 180 trees. A single acre of solar panels with a capacity of 250,000 watts can be expected to offset more carbon emissions than 6,500 trees.
So if the argument were purely based on emissions, a single residential solar installation is already worth more than a few trees. And a single acre of densely populated solar panels offsets at least 16 to 65 times more emissions than a forest of the same size.
Another encouraging fact is that the solar emissions offset value isn’t the final word on a facility’s offset emissions. Solar power facilities that are installed on top of well managed, carbon sequestering land may end up producing additional carbon offsets.
For instance, analysis suggests that an acre of grazed native plants underneath the solar facility may improve soil at a rate of 1 ton of sequestered carbon per year, and that carbon and other nutrients may accumulate for 12 to 15 years before the soil is fully saturated.
Researchers who modeled prairie grasses in the upper midwest United States, see that that native grasses planted as part of 10 GW of solar generation capacity would sequester 129.3 tons of carbon per hectare; that is 65% and 35% greater than either an agriculture or a solar-turfgrass scenario, respectively.
So while it is true that we need large swatches of interconnected, undisturbed nature to have a healthy environment that supports human life over the coming millennium, it is also true that cutting down some trees, in specific situations, provides a net benefit from an emissions reduction perspective.
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