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New water-cooling solar panels could lower the cost of air conditioning by 20%
Most of us have heard of solar water heaters. Now there's a solar water cooler, and the technology may sharply lower the cost of industrial-scale air conditioning and refrigeration.
The new water coolers are panels that sit atop a roof, and they're made of three components. The first is a plastic layer topped with a silver coating that reflects nearly all incoming sunlight, keeping the panel from heating up in the summer sun. The plastic layer sits atop the second component, a snaking copper tube. Water is piped through the tube, where it sheds heat to the plastic. That heat is then radiated out by the plastic at a wavelength in the middle region of the infrared (IR) spectrum, which is not absorbed by the atmosphere and instead travels all the way to outer space. Finally, the whole panel is encased in a thermally insulating plastic housing that ensures nearly all the heat radiated away comes from the circulating water and not the surrounding air.
Researchers at Stanford University in Palo Alto, California, recently placed three water cooling panels—each 0.37 square meters—atop a building on campus and circulated water through them at a rate of 0.2 liters every minute. They report today in Nature Energy that their setup cooled the water as much as 5°C below the ambient temperature over 3 days of testing [DOI: 10.1038/nenergy.2017.143] [DX]. They then modeled how their panels would behave if integrated into a typical air conditioning unit for a two-story building in Las Vegas, Nevada. The results: Their setup would lower the building's air conditioning electrical demand by 21% over the summer.
(Score: 4, Insightful) by Bill Evans on Tuesday September 05 2017, @12:25PM (15 children)
According to this writeup, they're not really solar panels, are they? They're just panels that sit on the roof, and don't depend on the sun for anything, and certainly not for generating electricity.
(Score: 2) by requerdanos on Tuesday September 05 2017, @01:54PM (13 children)
According the the explanation above, they work in spite of the sun, not because of it. My first thought was, "How is that solar? They work in the dark." Yet TFS actually says...
So the inescapable conclusion is: Either I completely misunderstand, or TFA completely misunderstands.
(Score: 3, Insightful) by Sulla on Tuesday September 05 2017, @03:02PM (6 children)
Marketing. I think it is safe to say a majority of people think solar is cool, so if you tack solar onto it people will think it is a good idea.
Ceterum censeo Sinae esse delendam
(Score: 3, Touché) by Thexalon on Tuesday September 05 2017, @03:27PM (1 child)
That reminds me, I need to up the price of my 100% organic solar-powered air carbon removers. That's a much better name for them than "trees".
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 3, Touché) by requerdanos on Tuesday September 05 2017, @05:04PM
Of course, trees actually *are* powered by the sun.
(Score: 2) by fishybell on Tuesday September 05 2017, @03:40PM (3 children)
My parent's house in has a solar water heater [wikipedia.org]. My mom is convinced it works by using electricity to heat the water. I even pointed out that there are only water pipes coming in from the roof, and she still won't believe it.
Calling these solar panels causes the same kind of confusion the solar water heater has: the word solar ends up equating to electricity.
(Score: -1, Offtopic) by Anonymous Coward on Tuesday September 05 2017, @03:58PM (1 child)
Your mom sounds like a typical Trump supporter
(Score: 1, Offtopic) by Sulla on Tuesday September 05 2017, @04:07PM
The stupid on one side will think that this is some sort of electricity generating home cooling super device, and the ones on the other side will be mad that the unsustainable usage of air conditioning is being subsidized. Both suck.
Ceterum censeo Sinae esse delendam
(Score: 2) by maxwell demon on Tuesday September 05 2017, @07:45PM
Well, in some sense it does: Light is an electromagnetic wave, and it heats up the water by acting on the electric charges in the solar heater's matter, causing its molecules to vibrate and transfer that vibration to the water. Were there no electrically charged particles in the matter making up the solar water heater, the light couldn't heat the water.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2, Informative) by Zinho on Tuesday September 05 2017, @03:12PM (5 children)
You are correct, and the headline is confused. The only connection these units have with solar panels is that they can both be mounted on a rooftop.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by GreatAuntAnesthesia on Tuesday September 05 2017, @03:55PM (4 children)
Could you mount one on top of the other?
(Score: 2) by bob_super on Tuesday September 05 2017, @04:25PM
Maybe, but what makes the confusion worse is you don't have to mount them on the roof at all...
By the way: Hey, I put ultra-reflective coatings on your Vegas roof and your AC bill dropped! Why did they bother with the water thing?
(Score: 2) by Zinho on Tuesday September 05 2017, @06:43PM (2 children)
No, the cooling panels radiate heat into space, and need a clear view of the sky to operate. You can't mount a solar panel above it; otherwise the equilibrium temperature of the water in the cooling loop will be close to the temperature of the solar panels (which get pretty hot). The right way to mount these would be to put solar panels on the south-facing slope of the roof and radiator panels on the north-facing side. [1]
[1] Bonus points for having asymmetric slopes; south-facing solar should be angled off of horizontal at the same number of degrees as the local latitude, north-facing slope should be at 90 degrees from the south to maximize view of the sky and minimize solar exposure. People who design earthship-style [cloudfront.net] homes would be able to incorporate this fairly easily into their roofs. [2]
[2] This assumes that the people who build earthships are into air conditioning, which they aren't. The earthship design calls for passive geothermal cooling for the air in the home. The shallow pitch on their north-facing roof slope is also already radiating heat from the home into space, so putting insulated boxes above it negates that benefit. Again, maybe in higher latitudes having the extra insulation would be good for winter time. Not sure where the system would fit into the summer operation of a proper earthship, but it's worth thinking about. Also, pretty much every house would benefit from having better roof design based on latitude, hence my use of the phrase "earthship-style homes" rather than simply "earthship homes". And now I'll shut up, because I've been rambling too long already.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 4, Touché) by maxwell demon on Tuesday September 05 2017, @07:47PM (1 child)
Some people live at a latitude of 45 degrees.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by Zinho on Tuesday September 05 2017, @09:29PM
Nice, that earned a "touché" mod from me. Well played.
I'd have no objection to people living at 45 degrees north or south of the equator having symmetrical front/back 45 degree roof slopes.
[aside]/Zinho looks up which locations lie on the 45th parallels[/slope]
Looks like New Zealand, Argentina, and Chile are the winners in the south. In the north it's France, Italy, several former Yugoslavian states, Ukraine, Russia, Kazakhstan, Uzbekistan, China, Mongolia, Japan, and the US States between Oregon and the northern border of Vermont. It would be an interesting exercise to build an Earthship up there and see the reaction it would draw on the permie message boards if I bought pre-fab trusses for its construction. :P
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by chromas on Tuesday September 05 2017, @07:57PM
Solar Freakin' Coolways!!!12
(Score: 2) by Runaway1956 on Tuesday September 05 2017, @12:55PM (5 children)
Three panels, each roughly 1/3 of a square meter. So, one square meter of paneling, or close enough for estimation. In the model, did they use an entire roof, or just their square meter of cooling panel? A typical roof ranges between 10 square yards (small home) to about 30 yards (fairly large home) and as much as 50 yards (big home, with built on garage). So, how does this thing work out if you put several square yards of paneling on your roof? They're plastic anyway, just make them roughly one square yard, and interlockiing, and use them for roofing material. Just cover the entire home with them!!
Yeah, I know, roofs don't typically come in multiples of yards, or meters, there will be cutting involved, which may destroy the panels. Then again, roofs can be altered to some degree, to make the panels fit.
Abortion is the number one killed of children in the United States.
(Score: 2) by Zinho on Tuesday September 05 2017, @02:50PM (3 children)
The test was just the single square meter. There was a pretty good picture of the setup [sciencemag.org] in the Science magazine article. At the moment they're pretty bulky, as would be expected from a workshop-style proof-of-concept. Shingle-style replacement for standard roof tiles is a long way off at this point.
The critical measurement from the article was that it rejected 70 W m−2 , so you'd need to scale up the installation significantly to handle the heat rejected by a typical air conditioner. At 1-2 kW per room that means your rooftop installation needs to have 28ish m^2 of cooling box on the roof, or about 300 square feet (= 33.5 square yards). That's about the area of the north-facing slope of my home's roof, so if I were to try this I'd either need to supplement with additional cooling or expand my installation to other areas beyond my roof. I'd realistically need ~12 times my roof's area to fully cool my entire house with this technology.
I imagine that this could be great for places further north where ambient temperatures aren't as high and less-direct solar flux improves the efficiency of these coolers.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 1) by j-beda on Tuesday September 05 2017, @03:34PM (2 children)
Of course these sorts of things don't have to do all the colling themselves to be useful. Combining them with a standard heat-pump/air-conditioner would imporve the efficiency of the AC unit and make it cheaper to run.
(Score: 1) by j-beda on Tuesday September 05 2017, @03:37PM
"cooling" rather than "colling" is what I meant to say. Not that anyone probably cares. Now I have to wait long enough to get over the "you just posted" barrier....
(Score: 2) by Zinho on Tuesday September 05 2017, @06:04PM
That's exactly the intent of the research, they want to give the A/C a better heat sink than ambient air temperature outside. A water bath cooled by these radiator panels would do the trick nicely, provided that the panels actually cool the bath faster than the A/C warms it up. That's where the 70 W/m^2 rating of the panels becomes important, it tells you how big of a radiator you need in order to handle all the waste heat the A/C produces.
PS - I don't normally change spellings when I quote someone else's post, but you mentioned it in a follow-up; I hope you're cool with the fix.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 3, Insightful) by JoeMerchant on Tuesday September 05 2017, @08:06PM
Any roof I've ever had gets covered with dust, mold, leaves, and other crud fairly quickly - like within a month or less of cleaning. This is a great theory, but basically it's trying to create a thermal diode radiating to space, and that radiation path is going to be pretty expensive to maintain in much of the world.
Україна досі не є частиною Росії Слава Україні🌻 https://www.pravda.com.ua/eng/news/2023/06/24/7408365/
(Score: 2) by anotherblackhat on Tuesday September 05 2017, @02:32PM (1 child)
I'm guessing they meant 70 watts per square meter.
This plastic http://www.sciencemag.org/news/2017/02/cheap-plastic-film-cools-whatever-it-touches-10-c [sciencemag.org] claims 40 watts per m2.
They might get more heat dissipation per area, but not more per dollar.
(Score: 1, Informative) by Anonymous Coward on Tuesday September 05 2017, @07:21PM
Remember that x^-1 is 1/x?
So you are correct that they mean Watts per meter squared, but their representation of it is perfectly acceptable.
(Score: 3, Insightful) by Sulla on Tuesday September 05 2017, @03:09PM (3 children)
It is applications like this that will start making a difference in lowering the carbon footprint. A possible 20% savings in power spent on air conditioning is a huge cost savings and they get to claim that they are green on top of everything else. The way to get people on board is to not call them evil planet murderers for wanting to drive their car, it is to invent tech to make their car not a problem to continue to use. Telling people to change will never work unless they are given an incentive to do so, I think we recently saw a study on here about how hope of monetary gain (sell as spending less on electricity) is much easier than selling impending doom.
Ceterum censeo Sinae esse delendam
(Score: 2) by JoeMerchant on Tuesday September 05 2017, @08:21PM
Yeah, this is real "green" technology, especially after the first idiot scrubs the mold off the panel with TSP and a thick layer of green algae grows back a week later.
Україна досі не є частиною Росії Слава Україні🌻 https://www.pravda.com.ua/eng/news/2023/06/24/7408365/
(Score: 1, Informative) by Anonymous Coward on Tuesday September 05 2017, @08:41PM (1 child)
While I agree that some tech can solve environmental problems, this device is probably not going to help much.
The relevant matter (which is rarely discussed) is net energy usage. How much is saved vs. how much is spent on adding this system (which is just a fancy radiator).
They're using plastic with lots of copper piping, that takes lots of energy to manufacture (although it should recycle better than old solar panels). Then there is the install and maintenance.
And how long does it last, it uses an active pump and piping so there are moving parts and water so probably less than 15-20 years before it all starts leaking and needs replacing.
Does 20% efficiency really offset all these energy costs for a complicated system that only produces 5°C? In most places you would be better off using ground coupling for lower temperatures, or using thermal storage to bank cold from lower night time temperatures. Or even more drastically not using the AC so much!
But this will probably sell, because you can show it off to your neighbors and boast about being green. Which is probably why they call them solar, they share that with many solar panel installations. Something I can point to and boast to the neighbors and say; look I'm green, I'm doing my part, while driving my single occupant SUV to the mall to participate in rampant consumer culture to the extreme and not making in real life changes.
(Score: 2) by gnuman on Wednesday September 06 2017, @04:23AM
1. It's copper pipes, so it's design life is far better than 20 years.
2. It can clearly operate as a passive system without moving parts.
I think they know what they are talking about here.
It's kind of amazing how simple solutions are immediately shouted down as impractical even if they are so much more practical than having 100% renewable power grid. This solution radiates heat away. It's simple and it has no maintenance issues. So of course, shout it down!
(Score: 2, Insightful) by Anonymous Coward on Tuesday September 05 2017, @04:19PM (5 children)
So as I understand it, the researchers are using some polymer which radiates energy in the mid-infrared spectrum, which passes through air. This process causes the material to cool, so they use it to cool water pipes in the obvious way. Then they insulate everything with material transparent to the emitted light.
This process has to be powered somehow, or we have a perpetual motion machine. The article does not describe how it is powered. This is published in Nature so the researchers are presumably not total cranks.
The heat pumps used in refrigeration are rather efficient, moving about 2-3 units of thermal energy for every unit of electrical energy. To reduce total energy usage this system will have to do better than that: if it takes, say, 100W of electrical power to run it has to remove heat at a rate of about 300W or more.
Sadly the article is light on details and the paper is paywalled.
(Score: 2) by Virindi on Tuesday September 05 2017, @04:27PM (1 child)
This is exactly what I was wondering. The summary seems to claim a device which transmits but does not absorb heat energy, thus allowing heat to move from a cold place to a hot place with no energy input. This would appear to violate thermodynamics. So what's the catch?
(Score: 0) by Anonymous Coward on Tuesday September 05 2017, @06:59PM
It seems to be a passive device that can radiate heat to space even when it is in full sunlight. An effective use would be to dissipate heat from an air conditioner's hot side. With nothing else in place, it can keep something below it about 5 C cooler than the ambient temperature above the panel. That would provide only a small amount of cooling by itself. The market for this would be to reduce the operating cost of an air conditioning unit.
(Score: 3, Informative) by leftover on Tuesday September 05 2017, @06:00PM
This technology was discussed a few months ago on a science-related site, can't remember which one. The one "trick" is that microstructures on the film surface cause it to radiate efficiently at a particular wavelength. The wavelength they designed it to use is not blocked by the atmosphere. Consequently the panel radiates to space in the ordinary hot-to-cold sense. Also, since the atmosphere does not interact with this wavelength it does not diffract energy back into it. As long as the panel never sees direct sunlight it will be cooler than ambient.
Any other activity in the system will certainly require power, i.e. moving the working fluid, running an associated heat pump.
Bent, folded, spindled, and mutilated.
(Score: 1, Informative) by Anonymous Coward on Tuesday September 05 2017, @07:06PM (1 child)
It doesn't need power, and is not a perpetual motion device. It is a means of radiating heat to space, and works even though it is in full sunlight. Thus it provides the advantage of letting an air conditioning unit operate more efficiently than if it were rejecting heat to the ambient air. The best you can do in the way of using this for perpetual motion would be to operate a heat engine between the ambient air as a heat source and this device's cold side as a heat sink. The difference is only about 5 C, so it would not be very practical. It isn't perpetual in the theoretical sense because you will eventually run out of ambient heat or heat up the universe.
(Score: 0) by Anonymous Coward on Tuesday September 05 2017, @09:59PM
A 5°C difference is plenty enough to generate useful work. Looking at the first peltier device I could find which included this information in the datasheet (Marlow RC12-2.5) this should generate approximately 5mW at 0.2V, with physical dimensions about 30mm x 30mm. Not a lot, but if this device can really do this then we can build an array of these.
Let's put 33 in series to get a nice 1m x 30mm row, producing a more useful ~6.6V, capable of outputting about 25mA. So we can put 33 of those in parallel to get a 1m x 1m panel, giving us about 0.8A maximum output -- around 5W. It'll be big and expensive but you can certainly run something off of that. Perhaps it would be useful for spacecraft. There may also be better peltier devices.
A solar panel will do better (about 30x more power for the same area) but it is generally easier to point something away from the sun than towards it.
(Score: 2) by richtopia on Tuesday September 05 2017, @04:41PM
The article is paywalled, so I'm not sure of the working model for this solar cooling system. I suspect that a traditional cooling tower will be more effective in all but the most humid climates or dry climates (cooling towers consume water, so if water is expensive a closed setup may be better).
Honestly all permanently installed air conditioners should have evaporative cooling.
(Score: 2) by Phoenix666 on Wednesday September 06 2017, @12:08AM
It seems a better use of that heat to dump it into the water heater. There are ground source heat pump setups that do that via a heat exchanger. Other potential uses are to radiate that heat in a greenhouse that contains tropical plants like banana trees or orchids, or to run a stirling engine.
As a civilization we have the technical means to manage heat and energy flow more efficiently, with no new innovations necessary. We ought to. Why don't we?
Washington DC delenda est.