True Co$t

There’s been no better embodiment of suburban green-vs-green tensions than the recent court battle between South Bay neighbors, one of whom claimed that the shade from a neighboring couple’s stand of redwood trees was blocking his solar panels. Both the tree owners and the solar proponent believed they were doing what was best for the environment, and the debate escalated all the way to Santa Clara County Superior Court. As solar power moves into more suburbs with close quarters, tall trees, and taboos against cutting down greenery, this issue is bound to flare up again. So which would win a green-off: trees or solar panels?

First, it helps to understand why solar installers are so crazy for unimpeded sunlight. Solar panels are made of individual photovoltaic cells grouped into columns. If one cell is shaded, production for that whole column shuts down. My brother-in-law Nathan Fleischer, a solar energy expert who spends his days figuring out the best placement for solar panels in schools, explained to me that if a branch casts a shadow along the bottom six inches of a solar panel, it will halt energy production for each column connected to those shaded cells. Even a little shade can have a big impact.

Weighing the benefits

Trees are famously good for the environment: they produce oxygen, create habitats for wildlife, filter noise, cool urban areas, slow soil erosion, reduce the run-off from heavy rains that can lead to municipal drainage issues and flooding, and break down pesticides and other groundwater pollutants into less dangerous compounds.

They’re also great for homeowners’ pocketbooks: planted close to a house, they will shade it from summer heat, reducing cooling costs. They provide shelter from winds in winter, lowering heating bills. The Center for Urban Forest Research estimates that after five years, a tree planted on the west side of a house will lower energy bills by three percent. After fifteen years, the savings rise to almost twelve percent. In short, when we plant trees, they repay us for our investment many times over.

Unlike trees, which take years to grow large enough to shade a house, solar panels start producing clean energy instantly. Manufacturing the panels uses energy from dirtier sources, but since the panels produce clean energy that emits no pollution or greenhouse gases, and use no fossil fuels, you compensate for that energy consumption pretty quickly. It takes between three and thirteen percent of the electricity generated over the lifetime of the solar panels to make up for energy used during their manufacture. That means you come out 87 to 97 percent ahead in the clean-electricity equation in the long run.

Solar power means clean energy not just for heating and cooling but for all of your energy needs, including lighting, cooking, and powering the television. It also directly reduces reliance on dirtier energy sources: for example, in PG&E’s 2007 retail customer electric power mix, 47 percent was derived from natural gas and four percent from coal. Solar power is already proving it can reduce dependence on such energy sources: according to CNN, last year solar panels on homes and businesses in California created as much energy as eight power plants.

What’s more, solar power gives back to the grid when demand is highest. Since it produces the most electricity during peak daylight hours, when energy is most expensive, it cuts bills and reduces the risk of rolling blackouts that can plague California summers.

Counting carbon

Both trees and solar power are celebrated as carbon dioxide management tools. Trees absorb carbon from the atmosphere and store it, creating a “bank” that’s cashed out only when the tree dies and decomposes. It’s hard to pinpoint the amount of carbon dioxide a tree can pull out of the air each year—it depends on its type and size—but estimates vary from sixteen to seventy pounds per mature tree. What’s more, by reducing the heating and cooling needs of homes, trees reduce the demand for energy from carbon dioxide-emitting fossil fuels.

But when it comes to carbon dioxide reduction, solar power really kicks bark. Current photovoltaic technology offers about twelve percent conversion efficiency, meaning it’s able to convert about that much of the solar rays it collects into electricity. At that level, it takes four years of the panels’ assumed thirty-year lifespan to pay back the energy it took to manufacture them, leaving 26 years of pollution and greenhouse gas-free electricity. Using US Department of Energy statistics, if the average American household produced half of its electricity with solar power, over the thirty-year lifespan, each home would keep 91 tons of carbon dioxide out of the atmosphere—plus half a ton of sulfur dioxide and nearly 650 pounds of nitrogen oxides.

Factoring in costs

Solar power may be more effective than trees in the fight against carbon dioxide, but it’s way more expensive. In some cases, trees don’t cost a thing: Utilities and organizations in cities around Northern California have programs offering free shade trees to residents. However, it takes years for trees to mature enough to provide the kind of shade that puts a dent in cooling and heating needs.

Solar costs are high, but credits, rebates, and subsidies make it more affordable. When I plugged in my location and average monthly electricity bill ($29) to the solar estimator at, I discovered that covering half of my electricity needs with solar panels would cost me $6,700 up front. The solar finder then calculated all the rebates and credits I’d be eligible for, including some from the state and federal governments and from Pacific Gas & Electric, and estimated that my total out-of-pocket cost would end up closer to $3,500.

Larger-scale production in the coming years will likely bring the cost of photovoltaics down, and some cities, including Berkeley and San Francisco, are looking into additional ways of making solar power more affordable for homeowners. There are also less expensive solar energy options, including solar heaters just for water, and thin film solar technologies, which need larger surface areas to make up for being less efficient, but are less expensive than photovoltaic solar panels.

No matter which you choose, it pays to make the effort. The US Forest Service estimates that mature trees add about ten percent to a property’s value, and you can bet that solar energy systems on houses are a selling point these days as well.

Balancing the choices

Do we really have to choose one or the other? In most cases, no. Select the right spot for new trees and solar panels, and you can have both while maximizing the benefits of each.

Trees do the most energy saving when they’re planted on the western and—to a slightly lesser extent—eastern sides of a house. (Shade trees on the southern side of a house increase the energy you’ll need for heating during the winter.) Solar panels, on the other hand, need a clear south and southwest path. So when it comes to location, trees and solar panels don’t need to clash. This doesn’t, of course, solve problems with shade from existing trees, but it does offer a clear set of guidelines for future planting.

When planting new trees, talk with your neighbors about your plans. Solar is on the upswing, and just because your neighbors don’t have solar panels on their roof right now doesn’t mean they won’t in five years. If your neighborhood has existing trees to work around, consider pole-mounted solar systems on sunnier parts of the property.

Also, choose your trees wisely. Deciduous trees help houses far more than evergreens because they allow warming light to reach the house in the chilly winter months. Likewise, trees with dense branch patterns aren’t as good as those with a looser, more open branching system. And even though big, long-lived trees offer a greater overall benefit when it comes to carbon storage, look for trees that, when fully grown, will be in scale with your neighborhood.

Finding solutions

So how did the battle between those South Bay neighbors end? The court ordered extensive trimming of two of the redwoods, but the controversy spurred a clarification of the California Solar Shade Act, which states that if the trees were there first, solar panel owners can’t force them to be trimmed or removed.

Finding that balance between trees, solar power, and neighbors in the coming years is going to be an issue that will mostly play out over the back fence, not in the courtroom, so it’s vital that we don’t start dividing into warring factions of tree huggers and solar purists. In the quest for a sustainable environment, let’s make the most of both, and do it alongside our neighbors.

When it comes to lawns, which is better for the environment: real or fake? Should you buy a new dishwasher or wash those dishes by hand? Send your suggestions for future columns to

Comments are closed.