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Solar panels not just cool for the environment but cool for buildings as well

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July 18, 2011

Tilted solar panels (front), create a stronger cooling effect than panels flush with the r...

Tilted solar panels (front), create a stronger cooling effect than panels flush with the roof (Image: USCD Jacobs School of Engineering)

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According to a team of researchers at the UC San Diego Jacobs School of Engineering, the solar panels sprouting on increasing numbers of residential and commercial rooftops around the world aren't just generating green electricity, they're also helping keep the buildings cool. The news that letting photovoltaic panels take the solar beating will reduce the amount of heat reaching the roof shouldn't come as much of a surprise, but the fact no one has thought to quantify just what the effects of rooftop solar panels on a building's temperature are is a little baffling.

Although the observations for the study were taken over the short period of three days in April this year, Jan Kleissl, a professor of environmental engineering at the UC San Diego, and his team believe they the first peer-reviewed measurements of the cooling benefits provided by solar photovoltaic panels. And despite the limited time, Kleissl is confident his team developed a model that allows them to extrapolate their findings to predict cooling effects throughout the year.

Using a thermal imaging camera, the team gathered data on the roof of the Powell Structural Systems Laboratory at the Jacobs School of Engineering, which is equipped with tilted solar panels as well as solar panels that are flush with the roof, while some of the roof is not covered by any solar panels at all.

Google Earth image of the Powell Structural Systems Laboratory with a tilted solar panel a...

They determined that during the day, the panels reduced the amount of heat reaching the roof by about 38 percent and as a result the building's ceiling was five degrees Fahrenheit (three degrees Celsius) cooler than the ceiling under an exposed roof. Tilting panels with a gap between the building and the solar panel that allowed air to circulate were found to provide a bigger cooling effect than flush solar panels. Kleissl and his team say the amount saved on cooling the building amounts to a five percent discount on the price of the solar panels over their lifetime.

Additionally, the panels help hold heat in at night to cut heating costs in winter. On the flip side, however, the panels would also keep the sun from heating up a building in winter and would keep the heat accumulated in the building during the day in summer from escaping at night. Therefore the effects effectively cancel each other out in many climates.

"There are more efficient ways to passively cool buildings, such as reflective roof membranes," said Kleissl. "But, if you are considering installing solar photovoltaic, depending on your roof thermal properties, you can expect a large reduction in the amount of energy you use to cool your residence or business."

The UCSD Jacobs School of Engineering team's study will be published in an upcoming issue of the journal Solar Energy.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
12 Comments

Sorry it's crap. Nice call again to make people believe that solar panels will solve the issues with the environment.

BUT who investigated the NET HEAT INCREASE of having a solar panel on your roof?

Lets put it in another way. I have a white roof which reflects 30% of the heating rays of the sun... I install a solar panel to convert 20% of the suns rays to electricity to power my fridge... which actually just generates heat and it's even a 99% effeicient fridge! Oh wait now my solar panel absorbs 80% of the suns rays to convert some to electricity and the remaining 60% just creates heat... But hey I don't care, my house keeps cool because it's shaded by the solar panel.

Please editors start to criticize in a meaningfull manner what we are doing! We are heating up the planet to get 'some' electricity!!!!

Philippe Heeren
19th July, 2011 @ 01:37 am PDT

Here in Canada, flat roofs would mostly be covered with snow in the winter, reflecting that solar light anyways, that supposedly would heat the building according to this article. Capturing the energy via a tilted solar panel, the sun's energy could be used to heat the bldg, instead of being reflected back into the environment. So they would be a cooling plus in the summer, blocking the light from absorbing into the roof (and the energy could be used to run air conditioners), and a heating plus in the winter (energy used to run heaters), capturing normally unused solar rays.

Leanne Franson
19th July, 2011 @ 01:55 am PDT

Phillippe - If your fridge is 99% efficient, think about what it's job is: it doesn't create heat with the remaining energy use, it _transfers_ it (takes it from inside the fridge, and puts it outside).

While it's not completely as peachy as you would want it, I think a basic conservation-of-energy map will help you see it's not nearly as dire as you paint it either.

Anyway, the extreme alternative is to forgo health, food, shelter, live in the open, and allow our evolution to let those of us who can survive... except that evolution has favored our thinking and manipulation (e.g. tool building) capacity, so here - naturally - we are.

Yarko
19th July, 2011 @ 07:47 am PDT

This is a great preliminary study, but it leaves me with a lot of questions, especially on the exact conditions of the experiment.

So, how much does just putting a plate of glass reduce the temperature?

Charles Bosse
19th July, 2011 @ 07:57 am PDT

All that was really proven is that building needs more insulation.

Slowburn
19th July, 2011 @ 11:01 am PDT

Slowburn got this one. More insulation equals reduced energy needs. The question is how long is the ROI, and is it worth it to a society that thinks houses are a short term investment.

kuryus
19th July, 2011 @ 01:24 pm PDT

Gee Whizzzz, Like this was not an obvious conclusion. What a waste of university education time. Its like when they reported that when large wind generators were installed it got warmer down wind. No Kidding ! Simple logical math. When you take into account the wind generator removing 15% of the "power" out of the air, your bound to have less air movement after the generator, hence less cooling of the land behind it (hot of course due to solar gain) Of course the opposite in the winter....

Erwin Lapschies
19th July, 2011 @ 04:06 pm PDT

Yes, yes, it's an 'obvious' study. But even 'obvious' studies need to be done. You can't just assume things. Perhaps this paper triggers a more thorough evaluation on the insulative properties of solar panels as compared to other materials.

And to Philippe Heeren, yes the energy collected is used inside the home to mostly generate heat, but at least this is transferring heat energy from the sun into heat energy from your plasma/lcd. Without the solar panels, the heat energy from the sun enters the home, then you turn on your air-conditioner which is powered by a big plant somewhere converting coal into electricity and pollution. The solar panels minimize this excess pollution. You should apply some critical thinking to your own comments.

Facebook User
19th July, 2011 @ 06:02 pm PDT

The solar panels would need to be spaced away from the roof for it to work and also cover the whole roof while allowing a massive air flow. Heat does transfer through panels after some time... Maybe Philippe should proof read a little

"Oh wait now my solar panel absorbs 80% of the suns rays to convert some to electricity and the remaining 60% just creates heat.".....Huh?

harry_72
20th July, 2011 @ 02:55 am PDT

Authors conclusion seems to be a little premature. In fact, the malls or for that matter air conditioned shopping centres are a cause of worry as they influence global warmiing. The ideal way to achieve cooling either to residential or commercial building is through plants around. That is how a city in India used to be recognized as 'Naturally air conditioned' city. One cannot compete with nature - vegetation, I mean.

Asoor Shyam
20th July, 2011 @ 03:58 am PDT

PV solar is all good, and the cooling effect is intuitive, I am sure that the Professors of thermodynamics could see that, which is why they probably didn't bother to do the research, the good thing about student projects is that Students provide cheap (free, actually negative) labour costs (Students pay to go to College).

Anyone can see that if the direct temperature in the sun is 70 Deg C and the ambient temp is 35 Deg C shading the roof has the potential to reduce roof temp by 35 Deg C..

Though if only part of the roof is shaded, the temperature Reduction will be averaged in the ceiling crawl space...

For thermal energy (heating) in winter, Thermal solar panels will likely outperform PV many times over. (as long as they are cleaned of Snow by either thermal flushing or sweeping.) If it takes 9 PV panels to provide 8kWh / Day (185W panels) and the equivalent area of 4 panels provides in excess of 12kWh/Day equivalent for water heating, or 6kWh in winter, likely that thermal solar wins, and in summer it provides all of the hot water needed in the building, while using PV panels for electricity to make hot water is just nonsense, with double energy conversion losses (Heat to Electricity to heat, versus heat to heat in an exchanger...)

Small scale Thermal solar has been used for many years in Europe and Scandinavia with great success for heating water... Just need to keep the snow off....

MD
15th January, 2012 @ 04:57 am PST

It amazes me how often you see solar naysayers exercising their jaws, only seeing the negative. Reminds me of comments I've read about the naysayers of horseless carriages in the late 1800's and early 1900's. Certainly there are issues to be solved, technologies to develop, but if we approach from the negative we get no where.

I see this as a starting point on the research, which by the way is pretty much where the article indicates they are.

I can envision the potential of panels that automatically change position; tiltied, raised, lowered, all to achieve greater efficiency.

While we certainly want to examine ideas in a critical way, they can still be positive examinations.

I suppose we could have stayed with horses, but then with the number we would need in use today the methane gas would be a really serious issue!

OPa_Infinity
16th January, 2012 @ 08:45 am PST
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