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Are Solar Panels Worth the Cost?

At a recent event on renewable energy choices, a proud homeowner showed a picture of his gleaming new rooftop PV array, and pointed out that he’d chopped down all the trees on his lot to make sure nothing got in the way of his roof.

I chuckled, having just planted some trees to save money on energy costs, which led me to ponder: tree or panel, which is greener? Is there an obvious choice?

Every ray of sunlight that doesn’t get through to a home’s exterior in the summertime is an air conditioning savings: it takes much less electricity to keep the house cool when there is no direct sun beating on it. The Arbor Day Foundation estimates that a few strategically placed deciduous trees can save 15-35% on annual cooling costs, and utilities are picking up on the idea: my trees were free as part of my local utility’s demand reduction program.

For the average US household in a single-family home, air conditioning represents 15% of all electricity expenditures. A 15-35% reduction in cooling needs means a reduction of 2.3-5.3 percent in total energy use or 300-700 kilowatt-hours (kwh) per year saved. That’s $35-$80 per year back in the homeowner’s pocket (at average US electricity rates). Using the low-end of the Arbor Day Foundation estimate (since many lots are already at least partly shaded or cannot be conveniently planted), the savings potential of tree shade across the US could be as much as 20 billion annual kWh of electricity, which don’t need to be generated.

Generating an equivalent quantity would require the installation of 2 million residential size, 5-kW solar arrays at a cost of 60 billion dollars (using figures from the Berkeley Lab Tracking The Sun 2011 installed PV cost survey). Of course, the homeowner installing the PV array will benefit from rebates, tax incentives, leasing options, save on his electric bill and might get some cash for the renewable energy credits.

For utilities, less load at peak times means better grid operation and savings on wholesale power prices to everybody’s benefit. That’s why many power companies are offering those tree-planting incentives. Solar plays a similar role in mitigating price spikes by increasing peak time supply.

The best part about trees is that they are free or heavily subsidized: rebates for shade trees are available all over the country, from SRP in Central Arizona and CPS Energy in San Antonio to Kaukana and Waunakee Wisconsin. In California, it seems like every local public utility has a tree rebate program: they are available in Annaheim, Pasadena, Roseville and Riverside. The Arbor Day Foundation has a program with several utilities to provide homeowners up to two free trees along with a cool application to find the optimal location to plant it to reduce cooling costs. The group just finished its spring shipments, which went from March through May, but the next round starts in October for fall tree planting season.

For those us with trees on our lots: don’t chop them down, shade is good! If you have the space to plant shade trees, ponder the tree to panel tradeoff – and where available, consider investing in a community solar project instead to offset your remaining air conditioning load!

…The only problem with trees is that they take time to grow, so plant sooner rather than later.

Veronique Bugnion's picture

Thank Veronique for the Post!

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Rosana Francescato's picture
Rosana Francescato on Jun 14, 2013 4:05 pm GMT

If you have enough space, you can put solar panels on another part of your property. Or if you live in a state with solar gardens laws, you can subscribe to power from panels installed elsewhere (see solargardens.org). Maybe it doesn’t have to be either/or. I love solar, but I’d hate to see people cutting down trees to install it.

Ivor O'Connor's picture
Ivor O'Connor on Jun 14, 2013 5:23 pm GMT

You could argue the solar panels give you shade and energy making them the obvious choice all the way around.

Furthermore though I like trees I will never ever plant a shade tree. Unless it also produces fruits or nuts.

Stephen Nielsen's picture
Stephen Nielsen on Jun 14, 2013 11:34 pm GMT

In the June issue of Popular Science, there is section about the future of solar. V3Solar has a two page spread as one of the solutions that “could usher in a new age for solar.”

…Worries over trees and or roof tops unnecessary…

Get ready for the revolution.

http://www.popsci.com/science/article/2013-05/future-energy-solar

Thomas Garven's picture
Thomas Garven on Jun 15, 2013 2:41 pm GMT

Hi Veronique:

Like so many things in life it all depends pretty much on where you live doesn’t it?.  While the Arbor Foundation does good work it really isn’t very applicable here in the desert Southwest.  Oh sure you will find a few trees in Phoenix or other nearby cities; but for the most part tree plantings are very limited.  Also pretty much gone are grass lawns which also reduce surrounding air temperatures and for two reasons.  Water conservation and who wants to mow and edge when it is 110 F outside, LOL.  

For the most part people living in the desert Southwest focus on energy efficiency, energy conservation, equipment design and placement and buy the most efficient heat pumps we can afford.  It is common for summer cooling costs to exceed 75% of someones total electric bill.  When I was selling solar PV to local homeowners it was quite common to see summer electric bills of $200-$450/mo.  For most calculations or comparisons between various parts of the country; just flip the oil heating cost of someone in the Midwest for our summer cooling cost.  Although our total cooling costs will most likely be less.  For many homeowners with a family of 4 it would take about 6-8 kWh solar system grid tied to zero out their electric bill if they were energy conscience. 

As I said above, for us, its all about insulation, window efficency, home design and equipment and for those that can afford it, solar PV to offset energy costs.  Trees are certainly something nice to have and I enjoy a nice specemin in my front yeard away from any PV installation.  Maybe we should be asking WHY he cut down his trees and if he left any at all on his property.  Was he just tired of mulching leaves, trimming and watering?  

Don’t know but in any case solar is HUGE where I live.  We have 3 companies employing probably 30 people working full time to handle the orders.  At the current installation rate we will most likely see 25% of all homes with solar installations in about 5 years.

All depends on where you live doesn’t it?  Have a great day and this is very well written piece.

Veronique Bugnion's picture
Veronique Bugnion on Jun 15, 2013 11:28 pm GMT

Hi Thomas,

Thanks for your thoughtful comment. My post wasn’t meant to be “anti-solar” by any means, I’m actually a big fan, it’s intent was much more to push people who have shaded lots or live in areas where trees are abundant, grow fast and water is plentiful (clearly not Phoenix!) to look at community projects rather than chop down trees.

The backstory on the image which prompted the post was that squirrels built a nest under one of the solar panels, which led to a fire. It didn’t destroy the person’s roof, his array or his house but prompted him to cut down the trees to avoid a recurrence … but given what he had to chopn down, I’m not convinced he was a good candidate for solar from the beginning!

Mark Tracy's picture
Mark Tracy on Jun 18, 2013 8:52 pm GMT

Jan Kleissl and his team at the University of California – San Diego Jacobs School of Engineering have what they believe are the first peer-reviewed measurements showing that solar photovoltaic panels on your roof can help insulate your house.

Using thermal imaging, they determined that during the day, a building’s ceiling was five degrees Fahrenheit cooler under solar panels than under an exposed roof. At night, the panels helped retain heat, reducing heating costs in the winter. Their paper was accepted for publication in the July 6, 2011 journal Solar Energy.

The panels essentially act as roof shades, according to team member Anthony Dominguez. Rather than have the sun beating down onto the roof, which causes heat to be pushed through the roof and into the ceiling of the building, photovoltaic panels take the solar beating. Much of the heat is removed by wind blowing between the panels and the roof. The benefits are greater if there is an open gap where air can circulate between the building and the solar panel, so tilted panels provide more cooling. Also, the more efficient the solar panels, the bigger the cooling effect, said Kleissl. For the building the researchers analyzed, the panels reduced the amount of heat reaching the roof by about 38 percent.

I K's picture
I K on Jun 26, 2013 11:33 pm GMT

if that is your aim why not spend two dollars on a tin of paint and paint the roof white, then we can wow at how great this side benefit is of decreasing heat gain into the house. or better yet why not take a picture of a PV panel and print it off and stick it on a piece of wood and put that on your roof. we can then wow at the heat reaching the rood reducing by 38% with just a picture of a PV cell.

oh the possibilities

Thom Westergren's picture
Thom Westergren on Nov 19, 2013 4:35 am GMT

There is a solution to the squirrel problem, aside from cutting back branches or whole trees. The space between the roof and the outer edge of the solar array can be screened. The best way to do this is with hardware that doesn’t harm the panels themselves (to maintain the waranty).

I have developed such a system and installers in certain locales are appreciative to have a simple, reliable solution. You can see it at www.spiffysolar.com.

Although this doesn’t seem to be a wide-spread problem, it can tend to be concentrated in certain regions or neighborhoods. Pigeons are an even more common under-solar-nester. They aren’t capable of the severe damage that squirrels can impart, but their nests and droppings can do a lot of roof damage—by retaining water. The mess and noise can be quite a nuisence, too.

As more and more PV solar is installed, installers will certainly see this problem with increasing regularity.

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