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The sun shall be neither mine nor yours - divide it!

The amount of energy the sun gives to the Earth on a constant basis is about 1.4 kilowatts per square meter at the Earth's outer atmosphere. Insolation is the amount of solar radiation that actually reaches a given spot on the Earth. On a sunny day, that insolation can be about 12 kilowatt hours per square meter. That's the same amount of energy contained in about 40 cubic feet of natural gas. Various sources have said that the amount of solar energy that reaches the Earth's surface in one year is 10,000 times greater than all the energy, of all kinds, that humanity uses in one year. That should be plenty to go around, right? We're usually more concerned about taking proper advantage of this free resource than divvying it up. But take the modern carbon economy, the growing legal infrastructure supporting it, and a good old-fashioned neighborly dispute, and you've got Sunnyvale, California environmentalists pitted against each other, fighting over the sunlight. The San Jose Mercury News reported recently that a Santa Clara County couple may be the first homeowners to be prosecuted under the Solar Shade Control Act, signed by Governor Jerry Brown in 1978 during the previous American solar renaissance. "We are the first citizens in the state of California to be convicted of a crime for growing redwood trees," one of them complains. The problem is that the couple's redwoods, planted for privacy and now 20 to 40 feet tall, are shading their neighbor's rooftop solar photovoltaic panels. The law prohibits trees or shrubs planted after 1979 from shading more than 10% of a neighbor's solar panels between 10 a.m. and 2 p.m. -- peak power-generating time. The image shown here, from Google maps, shows the home with the rooftop PV panels. This image appears to be taken in early afternoon, with shade from the trees (circled in white), owned by the homeowners to the southwest, having already crept onto the southernmost PV panels. Worried about setting a precedent for other tree lovers, the couple is fighting the law, which could result in fines of $1,000 per day and require them to remove their trees. The deputy district attorney in charge of the case simply says he's following the instructions of California's lawmakers. The case may become interesting for a lot more California homeowners, with aggressive new regulations and incentives likely leading to growing numbers of rooftop solar arrays. How would the case fare if we had some kind of impartial environmental court weighing true life-cycle costs of various choices? In today's carbon-hyped culture where emissions reductions are increasingly valued, the trees may have to come down. A local solar photovoltaic salesman and Sierra Club member puts it this way: "I'm a big tree fan. They increase property values and provide shade and cooling. But it's actually better for the environment to put solar on your roof than to plant a tree. On average a tree only sequesters 14 pounds of carbon dioxide a year and a solar electric system offsets that every two or three days." Carbon accounting depends on a lot of assumptions, and so the reality is a lot more complicated. For now, a Superior Court judge tried to split the difference, waiving any fines and ruling that only two of the eight trees need come down. The couple is appealing.

Published January 25, 2008

(2008, January 25). The sun shall be neither mine nor yours - divide it!. Retrieved from

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January 25, 2008 - 10:00 am

Planting trees around a building may shade the solar array, but they also shade the house and reduce the cooling load on the house (both through the shade as well as through the reduced heat island). As to which is better trees or solar, it really depends on the details of the house and the trees. I hope someone will compare the the actual CO2 reduction that the trees provide including both the tree's carbon sequestering capabilities as well as the shading benefits to the PV's capabilities for the judge.