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Thread: Solar Energy : Its behaviour when striking objects

  1. #1 Solar Energy : Its behaviour when striking objects 
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    Mar 2007
    Littlehampton, South Australia
    Solar energy I understand is composed of energetic objects called photons, massless particles that have wave-like properties. They arrive as "cold" bundles of energy and only when they interact with molecules, do we end up with "heat", which is actually a measure of the molecular vibration rate.

    I am trying to build a concept for how sunlight interacts with various materials because I think that most of the world is a little wrong in its current single-factor based thinking that CO2 {plus other greenhouse gases} rises are the sole cause of global warming. The prescription for treatment is also tackling global warming by reduction in CO2 emissions is also flawed logic I thing, when you take the time to consider the dymamics of what is happening.

    What I think needs to happen is a subtle re-direction towards what I believe is actually happening - that the Earth's heat balance is being upset by an increase in conversion of solar radiation into heat, an increased release of chemical energy that has been stored for milennia and also an increase in the insulating effect of greenhouse gases. You could add a fourth factor, the variability of solar radiation to come up with a more complete model of Earth's temperature balance.

    Albedo is not enough to describe what is happening
    What happens when sunlight strikes a solid object? Firstly, the colour or reflectiveness of the object has a major contribution to what happens with the incident light energy. If the object is white or highly reflective, most of the incident energy is reflected in the same form back out to space. The "whiteness" or reflectiveness is called the objects "Albedo".

    But, albedo alone does not explain the difference in heating that happens for instance when you compare a sheet of white painted corrugated iron and a piece of paper. On the one hand, the white corrugated iron reflects most of the solar energy unaltered towards the sky. Some of it does get converted to heat, as testified by the fact that when you touch the metal of a roof on a sunny day, it is still hot to touch. The rate of heating is much lower than that of a black roof on the other hand, because of the low albedo of the black surface. Most of the solar energy is absorbed by the black surface and converted into heat, most of which is subsequently re-radiated to the air, contributing to global warming.

    But what if you had a black painted piece of cardboard? Would it be hot. Well, the answer is yes there is some warmth generated by black painted or toner printed on white paper, but the resultant heat is nowhere near what happens on black metal.

    Clearly, there are two factors at work here and an examination of the substance on which the surface is applied deserves consideration. Broadly speaking, the metal roof and a piece of paper are fundamentally different structures at a molecular level. The one is a crystalline structure, with tightly and regularly packed molecules that have strong bonds. This is why metal can withstand the intense forces to which it is subjected without breaking up.

    Morphousness versus Amorphousness may be the key
    Paper, cardboard and timber and amorphous structures, with complex hydrocarbon molecules arranged more loosely than you will see in metal. They are also arranged in cellular arrangements {in timber at least} which are subdivided into cellular walls {made up of lignin} and voids - made up of air.

    The way this type of material interacts with sunlight is fundamentally different and I would like to know why.

    My theory is that the metal on the one hand, because it has a crystalline structure interacts with the photons of sunlight to induce standing waves or vibrations in the surface layer. Imagine molecules of metal being represented as balls floating on water and photons being smaller balls raining down. The steady stream of photons hitting the much larger balls of metal molecules would induce a standing wave in the surface layer.

    This introduces another concept that I have not see written before, that photons have "kinetic force". We know this to be existent by the reality of the little photo kinetic toy - an evacuated glass bowl that contains a set of diamond shaped metal blades where one side is mirrored and the other black.

    Place this object in the sunlight and it starts spinning. The kinetic force of light at work. How large this force is is a question for another day. I think it is much larger that is currently thought.

    Because metal is a multi-layered crystalline structure, the vibrations that are established at the surface are transferred throughout the metal {by conduction} and to the surrounding air {radiation}. This is what happens to the energy of photons that strike metal, resulting in their conversion to heat.

    The first law of thermodynamics is remembered here in that "Energy can neither be created nor destroyed, but transferred from one form to another". No problems with this and the behaviour of sunlight interacting with metal is easily explained by the application of this principle.

    It means that where for instance solar radiation of say 500Wm-2 is showering down on a piece of metal then if it is black then nearly the same amount is being re-readiated into the surrounding air, once the metal heats up to its equilibrium temperature compared to the surrounding air.

    What happens to sunlight when it strikes amorphous substances?
    My real problem is with dealing with what happens to sunlight when it strikes an amorphous substance such as wood, cardboard or paper. Some of the energy is reflected, especially if the surface is white. But, some is absorbed, particularly if the surface has a low albedo. At a molecular level, photons may induce vibration in the surface layer of the material, but because of the more "open" molecular structure of say timber, standing waves cannot be generated to allow the energy to march throughout the substance. On a microscopic scale, the air particles trapped within the timber also stop the progress of heat through the substance by a process known as insulation.

    We also know that unlike transparent materials {glass and water for example} the energy does not permeate the material and transmit through to the next substance. Wood for instance is opaque - meaning no light energy passes through it.

    My real problem is: What happens to the surplus energy?

    Can it be that it simply vanishes or is locked away in some mysterious way into the amorphic structure of the surface involved? This does not seem consistent with the first law of thermodynamics and so I would like to know what has happend to the energy that neither becomes reflected, transmitted or converted into heat. Is it that the energy of photons is in fact turned into the kinetic energy of motion in the molecules making up the amorphous substance, but that some how because of the nature of the molecular-molecular bonds, this increased energy level is not translated into heat.

    Can you see my dilemma?

    Calculating a Solar Energy->Heat Conversion Ratio
    Given that what is observe in nature is true then the task is to derive a formula that describes the conversion of heat from sunlight and apply this to a strategy to reduce the net heat production from surfaces on Earth. From the foregoing discussion, one factor, the albedo or reflectiveness has to be a component. This alone as has been pointed out does not describe fully the observations made in the field.

    A second factor that I will term the "Amorphousness" of a substance needs to be invoked, to explain the difference in heat conversion that happens with sunlight and a piece of white paper and a sheet of white painted metal. On this amorphousness scale, metal would be 1 and paper near zero.

    Most people talk about reflectivity being equivalent to Albedo, but if you were interested in calculating the heat production from the interaction of sunlight and the material involved, an inverse function is more appropriate. At the risk of being accused of being a neologist, I term "Negrido" the inverse measure of an object's Albedo. For instance, a white object with the highest reflectivity {Magnesium carbonate} of say 100% would have a negrido value of zero.

    Now, by a simple formula of ....

    Negrido Value X Morphousness = Solar radiation:Heat conversion ratio.

    Putting these figures to work, let us examine the white paper versus white metal situation. The actual figures used here are not based on any measure, just plucked from estimates using background reading. To date I have not been able to find actual figures to describe what is being talked about here. All I am trying to do is to get a qualitative discussion happening first. A quantitative project may ensue and would be interesting I think. Perhaps this data does exist and will be very useful.

    The surface white has a Negrido value of 0.1
    Paper has a morphousness value of 0.1 and metal 0.9

    Then, given a solar radiation of 450 Watts/metre square, what is the anticipated heat generation from placing these two objects in the sunlight. ? Ignoring startup time for the system to reach equilibrium and assuming the solar radiation rate is constant, then the formula to be used is...

    Negrido Value X Morphousness X Radiation Rate

    For paper: 0.1 x 0.1 x 450 = 4.5 Watts/metre sq.
    For white painted metal: 0.1 x 0.9 x450 = 40.5 Watts/metre sq.

    Now, we do the same thing for black surfaces, where the negrido value for black is 0.9

    For paper: 0.9 x 0.1 x 450 = 40.5 Watts/metre sq.
    For black painted metal: 0.9 x 0.9 x450 = 364.5 Watts/metre sq.

    What consequences are there for this observation?
    The consequences for these differences are significant when we view the way mankind goes about making structures in which to live, work and play. Examining the theoretical heat generated from the surfaces that make up walls and roofs, it could be imagined that by applying this principle we can change the amount of energy from the sun that is converted into heat by passive surfaces {eg rooftops} in a range that has two orders of magnitude. {ie 4 ~ approx 400}

    If we started building houses with white roofs and amorphous substances then the amount of heat generated by the passive interaction between sunlight and the roofing material would be enormous. If you work out the heat generated by a black metal roof {which unfortunately is the urban dweller's favourite material so it seems} then the heat signature that a single dwelling makes is around 6~10x the heat signature that is produces from the dwelling's occupants use of electricity generated from coal fired power stations.

    Maybe it is time to rethink a few things before we rush in and close down industry that uses coal when by some simple changes we can at least make the heat signature of every building negative when compared to the background of the virgin land on which the building is placed. Repeat this millions of times and at least the local weather of cities would be altered, making them cooler and maybe with increased rainfall.

    It would not be too hard to turn the millions of tonnes of newsprint and plastic into a substance that is white and amorphous and could be sprayed onto every roof in the Earth, reducing the passive heat gain by many gigawatt hours per year. The passive heat production for a city is about somewhere between 100 X and 1,000 X the heat released from the coal fired power stations that supply the city with electricity! How cheap would it be to make a real difference by using waste products to cut our cities' heat generation.

    After all, Global Warming is about heat, not CO2 primarily. Fix one and the other may be resolved by nature. Give the oceans that chance to cool down and algae will do the job of carbon sequestration. What they need is temperatures to be no more than 16C. Cool down the cities and their local rainfall will increase. Forests will thrive and CO2 will be sequestered. It's simple logic - do something small that gives an amplified effect and we are all better off. The beauty of this concept is that local cooling benefits the citizens in the local area {through decreased energy requirment by living in cooler houses and more rainfall to keep their gardens looking nice, promote agriculture etc etc}. This makes the capital expenditure reasonable.

    The world benefits as well, because each megajoule of heat not generated is a megajoule that does not go into the heat balance system of Earth. Distal peoples will benefit from repeated local citizens activities.

    Contrast that with the one-factor model of global warming and CO2 reduction has the major fault that only when CO2 levels are globally reduced to around 300ppm will the weather start to change back to what was considered "ideal". Even if we stop pumping CO2 into the atmosphere today, the CO2 levels will take at least 100 years to spontaneously resolve, even if global warming does not induce further natural releases of Greenhouse Gases such as from the destruction of our northern forest by a run-away spruce beetle that is devastating coniferous forests across the Northern Hemisphere.

    When the permafrost starts to melt and the stored clathrates start to be released {methane gas trapped in ice} then it will be all over red rover. The prophecy of doom as put forward by people such as James Lovelock will have come true. We are so close to this happening and so the sense of urgency is real and accelerating, but for most of humanity, it is blissfully unaware of the impending doom.

    But in my enthusiasm, I digress. My question today is: What happens to the solar energy that is absorbed by amorphous substances?

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