That's neat. The nearly-black solar panels absorb light that the desert sand would have bounced back into space. So, simulations to the contrary, the solar panels probably wind up creating net global warming.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Net *local* warming more like.
What's the ratio of the PV array surface area to surrounding areas? Average temp increase over the total?
PV array structures are likely to be similar in thermal characteristics to all sorts of other man made structures eg factories, city buildings etc, etc. What's their contribution to the local warming?
Kindergarten-level analysis..
-- Cheers, Chris.
I'm sure Sloman will respond to this one as it is a mistake Larkin often makes and Bill corrects. Larkin doesn't understand the difference between creating heat and causing AGW. AGW has to do with the creation of greenhouse gasses that affect how the earth retains the *huge* amount of heat absorbed from total solar irradiance. The small amount of warming caused by the temporary absorption of heat by the solar arrays pales in significance. The impact of burning fossil fuels releasing carbon into the atmosphere has a lasting impact over many decades. This is not at all like the amplifying effect in a transistor, a small signal impacting control over a much larger power source. In effect photovoltaic power generation is an inverting amplifier of heat.
If the local creation of heat were a significant factor in AGW, nuclear power would be only a little better than photovoltaic with thermal efficiencies of 33% and 20% respectively. John seems to be a big advocate of nuclear power which, if local heat generation were a significant factor, would make nuclear power generation nearly as bad as solar. In reality neither is very bad since local heat generation given these numbers is just not a significant factor in AGW.
Oddly enough John argues that AGW is a good thing as raising the atmospheric carbon content is good for growing plants and a warmer earth should reduce energy consumption for heating, if I remember correctly. So why is he complaining about the energy released by photovoltaic inefficiency? Or maybe his real objection is the reduction in global temperature caused by the use of photovoltaic generation? In other words, John objects to anthropomorphic global cooling?
John seems like a highly intelligent person, very good with math. I don't get why he doesn't understand simple relationships like this... but then he claims he isn't so good with math and prefers simulations or just building things and tinkering with them to make them work. However the simulations of AGW show it to be a problem which he refutes and unfortunately tinkering with the real system can prove disastrous if controlled incorrectly. I guess he will never understand...
-- Rick C
Correct, but..
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Are you ring to confuse the ignorant or stupid? Energy (heat) does not stick around. Laws of thermodynamics guarantee that. Net effect is the stated increase; eventually everywhere.
its all about the Albedo
AGW believers believe that CO2 is changing the albedo.
Filling a nearly white desert with nearly black panels does change the albedo such that more net energy is retained on Earth.
This has little to do with AGW. AGW is an effect of CO2 and other greenhouse gases trapping heat so it does not get radiated as easily. This will impact the entire earth until the gas is absorbed or converted to something else. The increased heat absorption only has a short term impact over a limited area, such the name, "heat island".
-- Rick C
That's interesting. A solar panel turns (say) 10% of the light into electricity. But absorbs almost all of it, if the light had bounced off desert or forest or snow, then more would be reflected. (a roof
I was going to suggest that at night the solar panel would radiate more and reduce the total energy, but I'm not sure that's true. If the panel is up in the air it will cool, but couple poorly to the earth around it. Unless there's some wind...
(It's not at all obvious how the numbers would work out. Someones probably done the calculation/ approximation.)
George H.
They don't. The albedo is the amount of light that is reflected by a surfac e.
CO2 affects the attitude from which particular bands of infra-red radiation get emitted to outer space. If the effective emitting altitude gets pushed higher, where the air is colder (look up "lapse rate") there is less emiss ion at that wavelength and the temperature at ground level gets pushed up a bit to keep absorbtion and emission in balance.
bedo such that more net energy is retained on Earth.
Dessert sand has an albedo of 0.40. It's not "nearly white" like fresh snow (0.8-0.9) and ocean ice (0.5-0.7).
Solar panels may absorb more light, but they aren't going to cover an entir e desert. One hours worth of the solar radiation absorbed by the earth matc hes the amount we generate every year. We'd have to expose 0.01% of the ear th's surface as solar panels to capture what now need.
Real solar panels only see the sum for less than half the day, and only cap ture about 20% of the incident energy. 0.1% coverage would probably do it.
This isn't going to mess with the albedo enough to matter, or as much as we 've already messed with it by reducing the ice cover on the Arctic Ocean an d the snow cover in the northern hemisphere.
John Larkin can't - or can't be bothered to - do quantitative thinking. He consequently recycles a lot of lying propaganda that he ought to have been able to recognise as such.
He also likes Donald Trump ...
-- Bill Sloman, Sydney
Of course it is true. Otherwise you could accumulate energy just by the differential in radiance without having a difference in temperature. Black absorbs more and emits more energy.
Still, this issue is a red herring. The question is not does the solar panel absorb more heat that the ground it is built over, the question is what is the *net* effect of installing solar panels which preclude the burning of fossil fuels. Is the added heat absorbed by the solar panel greater than the heat that is blocked from being emitted from the earth by the increased greenhouse gases from burning fossil fuels? I think you will find the change in albedo has a much smaller impact than the effect of the greenhouse gases.
-- Rick C
Your guess would be true if the electricity generated by the solar panels were not used to displace electrcity generated by burning fossil fuels, which would have caused greater warming.
Similarly, roads absorb sunlight and get hot. We should ban them, or paint them white. Seriously, if you use air conditioning then it is very likely worthwhile painting your roof with a paint that reflects the wavelengths in sunlight, i.e. the visible and very importantly also the near-IR.
I was wondering if the appearance of a highly efficient solar panel (such as the type used for satellites) changes at all when it is shorted vs. open. Anyone know?
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
Like a car roof the isolated solar panel will get colder than the ground would have done.
I don't think it makes that much difference in the visible or near IR although the temperature of the panel might be noticeably different with/without current flowing to an external load.
Relatively recently someone made a designer structure that essentially is black in thermal IR atmospheric window and white almost everywhere else. It absorbs very little energy but is still a good radiator.
Such a material actually cools itself by radiation in direct sunlight.
(abstract only - paywall article for non academic use)
Popular science article
-- Regards, Martin Brown
Yes this is exactly my point.
OK you can think all you want, me, I want to see someone's numbers. (or do them myself.)
Solar panels have only recently passed the break even point, where they will produce more energy in their lifetime than they cost to make. A small added "energy cost" in terms of alebdo may be enough to tip the balance back the other way... I don't know. But I think it's an interesting question.
Georg eH.
Not me.. but open circuit the diode is forward biased and (I think) the photo current is just matching the normal forward current... so the only real difference is that the voltage is increased a bit... It doesn't seem like that would change the absorption probability that much. (I'd be happy to have someone tell me I'm wrong.)
George H.
Don't think so. Carriers are still generated, but they recombine fairly deep inside the silicon (open circuit) or at the pads (short circuit).
You could probably devise some optical measurement to detect the difference, but it's unlikely there would be any visual effect.
Adjacent panels with very different loads would run at different temperatures, of course.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Open circuit there will be no electric heating of the interceonnects (which would be present if it was shorted), that may be visible to thermal imaging, other than that, both ways, the panel is absorbing the same amout of light and producing the same amount of heat.
If the panel has a real load on it then it will be cooler than an unloaded (shorted or open-circuit) panel.
-- This email has not been checked by half-arsed antivirus software
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Evidence? Payback time has been five to seven years for quite a while now, and the lifetime is supposed to be about 20 to 25 years.
Not really. Solar panels would need to cover 0.1% of the planetary surface to collect all the power we currently use. A 0.1% change in albedo isn't go ing to matter - particularly when the albedo of the "perfectly white" dese rt sands John Larkin expects them to cover is only 0.4.
-- Bill Sloman, Sydney
Plenty, and birds have noticed. In colder climes, they fly in to the cities at night to keep warm.
Sylvia.
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w, and the lifetime is supposed to be about 20 to 25 years.
e to collect all the power we currently use. A 0.1% change in albedo isn't going to matter - particularly when the albedo of the "perfectly white" de sert sands John Larkin expects them to cover is only 0.4.
Hmm where do you get your numbers from...This (big file..)
This seems OK for payback time,
George h.
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