Doonesbury by Garry Trudeau for August 07, 2011

I hope they manufacture the coating in the US and not in China.

Actually, it wouldn’t be that hard to create a thermochromic coating – I wonder if it would be cost prohibitive. There are a lot of them out there that react to freezing temperatures by turning different colors.Any chemists in the readership? White when the material temperature is 65F + say, and black below that?

How bout a black tarp??

How bout a photovoltaic covering that generates electricity?

Check this out:…………………………………. North Carolina State University scientists are hoping that by imitating the leaf — biological perfection when it comes to turning light into energy — they’ll also improve our mechanisms for collecting solar power.Current solar cells use silicone as their basis, but recent findings by the North Carolina team show that water-gel-based solar devices can also produce electricity, according to Science Daily. The study, published by lead author Dr. Orlin Velev in the Journal of Materials Chemistry, experimented with water-based gel infused with various light-sensitive molecules and paired with carbon-coated electrodes. While synthetic light-sensitive molecules produced results, so did natural ones like chlorophyll, repurposed to produce electricity instead of sugars like it does for plants.Velev hopes that the natural materials could help eventually make a solar cell that’s cheaper to manufacture and better for the environment. For now, he’ll try to make the cells even more like the leaves they’re imitating: “The next step is to mimic the self-regenerating mechanisms found in plants. The other challenge is to change the water-based gel and light-sensitive molecules to improve the efficiency of the solar cells.”The water-gel-based cells are still fairly inefficient, but Velev already imagines a future where a leaf-covered roof doesn’t mean you should drag out a ladder.………………………………….

.Source:. http://blogs.howstuffworks.com/2010/09/29/artificial-leaf-generates-electricity/

Actually I have a photovoltaic on my roof. My power bill is oftern close to zero and occasionally I get money back because I generate enough electricity to contribute to the grid. This is becoming very common in Australia. Perhaps there’s an opportunity in the US for the same initiative…especially in the southern states where there is more sunlight and a need for more air conditioning.

Mood rings turn black when it’s cold…

What a great bunch of comments! Not one of the political duff that is seen so often. Hope the powers that be pick up on these ideas.

Mike, you have it wrong! A white roof is better in the summer too! A black roof radiates more heat than a white roof, and that is the dominant effect during most of the 24 hours. So a white roof reduces your heating bill.

Where I live, roofs are often white in the winter.

This is easy. The desert Beduins solved a similar problem ages ago related to the color of the long, hooded burnooses they wear as outer garments. It was noted that men who wore dark colored burnooses seemed as comfortable in the hot desert sun as those who wore all white. When scientists studied this they found that Arab men wear the same puffy light-weight innrt garments, which insulated them from their outer garments. A black burnoose worn outside this layer would absorb more sunlight than a white one and its surface temp would therefore be higher; but by the same token it would also radiate more energy back into the environment. As long as the individual wearing the dark burnoose was sufficiently insulated from it by the appropriate undergarments, the higher equilibrium temperature of the outer garment would not make him hotter. Application of a similar principle to roofs would seem straightforward.

I’d like to run an idea by Bernie: solar roof panels that are also skylights………also, natch, smaller houses, shade trees, and conserving coolth in summer, heat in winter by savvy opening & closing of windows and drapes

Ahh, I’ve missed Bernie since his college werewolf days.

How about a translucent solar array with an “electronic Ink” underlayment, the same technology as the Kindle? White during the summer and changing to black at a certain temperature threshold. With electronic ink you can vary the shades of white to black, with 100’s of shades available. With water pipes underneath you have some heat assist from the sun that could help heat water. The translucent solar has been done in the lab but not commercially at this point. Whoever can put this together as a single inter-lockable and scalable panel will make… billions!!

Re: the ‘natural leaf’ idea . . . I’m reminded of a theme Frank Herbert often wove through his science fiction novels. It’s the idea of genetically modified ‘flesh’ (with a nervous system, but no brain) that can be used for building material, furniture, etc. It responds to stimuli as a living thing (chairs that ‘wrap’ around you as you sit) and needs to be ‘fed’ with nutrient paint.

The basic point is that black surfaces both absorb and radiate faster than white surfaces. Therefore, if you want a temperature difference between inside and outside, in either direction, a white roof is better. If a black roof absorbed heat faster but did not radiate it faster, it would violate the second law of thermodynamics, which is a lot tougher than violating a human-made law.

Maybe someone should check out the Clinton initiative? They have been reducing energy costs in New York city for all types of buildings including the Empire State Building. A lot of homes in New Orleans have been built using solar panel roofs and other energy saving technologies. I see homes in the Northern latitudes using solar panel roofs also. They are almost invisible to the casual observer. (look like glass roofs -skylights- in some cases)

My flat roofed home had numerous leaks until we had a white rubberish material put down. It’s called Duralast and was developed as a pool liner. Did have to have it replaced this year after many hail storms, but it was 16-17 years old. Great product.

Perhaps they’ll use the same material used to make those glasses that change in the sun.

tell me more

I’m all for a green roof. The idea of the colour of the roof is one way. But what about actually “greening” your roof? You don’t need bushes or trees, but a drought resistant grass on your roof will not only help keep you cooler in the summer but will reduce heating costs in the winter. Natural insulation.Our new Trade & Convention Centre (in Vancouver) has the grass roof, uses recycled water, and most of the interior wood is from pine beetle destroyed pine trees. – Just remember sod houses in the pairaries.

This problem was solved by child inventor years ago. He designed a roof that consisted of angled panels alternating black and white. The angles (determined by latitude) were selected so that the white panels were exposed to direct sunlight when the sun was high in the sky during summer, and the black panels were exposed to direct sunlight when the sun was low in the sky during winter.He won an award, but I’ve never seen his idea implemented anywhere.

When I lived in Sunnyvale, CA. Which is next door to NASA’s Ames research center, a scientist there, Kenneth Billman (a friend of mine), and some of his collegiate scientists at NASA, came up with SOLARES..SOLARES puts mirror reflecting disks in low earth orbit (LEO), thousands of them, each has the area about the size of a football field, only it’s round, a circle shape. Each is like an umbrella in that it is “folded” for launch and then opens upon reaching LEO “opens” or deploys. They’re strung out in a great circle around the earth. Standing on the ground at night and looking up at them they would appear as a “string of pearls” stretching from horizon to horizon. Each “pearl” would appear as a very faint, barely visible star. Very beautiful, I would imagine. .Each mirror has a gyroscope, a motor powered by an on-board photovoltaic battery, and a tiny computer whose job it is to continuously orient the space mirror to reflect sunlight 24 hours per day, 7 days per week, 365 days per year (24/7/365) to receiving stations on earth. The stations are spaced around the earth like little “towns”. Each “town” operates 24/7/365 — whether day or night, any latitude (except very near the poles), any longitude. Each mirror switches its beam from “town” to “town” as it orbits. .Each “town” consists mainly of photovoltaic cells that convert the reflected sunshine from the space mirrors into electricity. The electricity, in turn, can be transported out in all directions, 360 degrees, essentially to any population center on earth. (There can be anchored, floating “towns” anywhere on any ocean as well, except maybe the (north) Arctic Ocean.) .Enough electricity can be generated to power the entire population of the earth essentially forever. Vastly more than all the oil fields, all the coal fields, everywhere. (This only depends on the number of orbiting mirrors and the number of “towns”.) .Furthermore, generated electricity on-site at any “town” can be used to convert or “split” water into pure hydrogen (fuel, etc.) and pure oxygen (many uses), each of which can be transported to points anywhere. (Even gasoline could be synthesized, though that should be “frowned on” as not supporting our clean energy future.).Bottom line: Enough clean energy, enough anything (essentially).

Trudeau has been cracking me up for decades. I love that guy.

Dear Mr. Trudeau and fellow Doonesbury fans,This happens to be my field (cool roofs), so it’s fun to see it in Doonesbury.The short answer to Mike’s question is that the summer cooling savings associated with substituting a white roof for a black roof are much greater than the winter heating penalty, primarily because in cold U.S. climates a roof receives about three to five times more daily sunlight in summer than in winter. (In winter the sun is low, the days are short, and the sky tends to be cloudy.) Hence the annual net energy cost savings (annual cooling energy cost savings – annual heating energy cost penalty) is positive nearly everywhere in the U.S.There are three further issues with switchable roofs.1. The small magnitude of a white roof’s annual heating energy cost penalty limits the potential benefit of switchable roofing. That is, a switchable roof would save more energy than an always-white roof, but not a lot more.2. The added benefit of a switchable roof is nil when the roof is under snow, because all snow-covered roofs are white.3. The switching method would have to be electrochromic, rather than thermochromic, because a thermochromic roof will tend to suffer from a negative feedback that drives it toward gray. That is, a thermochromic switchable roof will darken as it cools, but getting darker will make it warmer, which will make it lighter, which will make it cooler, and so on.)Hope this helps!- Ronnen Levinson, Staff Scientist, Heat Island Group, Lawrence Berkeley National Laboratory, RMLevinson@LBL.govP.S. For more about cool roofs, including maps of energy savings and penalties, please see R. Levinson and H. Akbari. 2010. Potential benefits of cool roofs on commercial buildings: conserving energy, saving money, and reducing emission of greenhouse gases and air pollutants. Energy Efficiency, 3 (1), 53-109. http://dx.doi.org/10.1007/s12053-008-9038-2Cool Roof Q+A. http://coolcolors.lbl.gov/assets/docs/fact-sheets/Cool-roof-Q%2BA.pdf Map of the ratio of mean global horizontal solar irradiance in winter to that in summer, illustrating how the northern mainland U.S. (latitude >= 40°N) receives 3 to 5 times as much daily sunlight in summer as in winter. http://bit.ly/pJOYSP

In some places in the world in never gets that cold, so having a white roof is a win win situation. I live considerably south of the Tropic of Cancer and about 2 years ago replaced my dark green roof with a white one. So yeah, it’s a good idea if you live in the right area.

What happens when it’s covered by snow? Then its thermochromatic properties would be inhibited by the coverage until the next thaw.