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Thread: The Bright Side Of Our Energy Scenario

  1. #1 The Bright Side Of Our Energy Scenario 
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    Princetonís nanomesh nearly triples solar cell efficiency | ExtremeTech

    Let us safely assume that by the end of this half-century, we have organometallic solar panels capable of >90% conversion of all parts of the spectrum.

    Here is a scenario I would like to put forth, and subject to criticism.

    Step 1: This theoretical panel with >90% efficiency for the entire spectrum is still electromagnetovoltaic (a superset of photovoltaic cells). So no turbines/heat exchanging fluid required.

    Step 2: The panel can be "stitched' onto thin layers of shape-memory cloth.

    Step 3: A satellite with "huge" (Order of magnitude, 100x100 metres or around) panels is sent into space. We're also assuming that this is economical enough that the cost is broken even in a matter of, arbitrarily, 2 years.

    Also, the satellite is in sun-synchronous orbit.
    ------------------------------------------------------------------------------------------------------------------------------------------------
    Now, for a few facts.

    1. The Solar Constant in orbit is: 1.361 kWh/m^2 (Solar constant - Wikipedia, the free encyclopedia)
    2. The panel is 90% efficient. (reasonable assumption in 40-50 years)
    ------------------------------------------------------------------------------------------------------------------------------------------------
    Now, for my questions:

    1. Assuming the energy stored in the satellite is beamed down to earth in the form of a laser beam, what type of efficiency, and what order of mag. of wavelength are we talking about to achieve optimum efficiency?

    2. For convenience, let us say we need to store the energy on board the satellite, what type of capacitance are we looking at? Also, the voltage,what type of voltage are we looking at?
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    The Amateur Calculations

    Solar Constant s=1.361 kWh/m^2
    Satellite-borne panel efficiency E1=0.9
    Transmission efficiency Et=0.95
    Receptor panel efficiency Er=0.9
    Satellite-panel area A=10, 000 m^2

    Total energy from 1 such satellite available to earth=

    s*A*E1*Et*Er=10, 472.895 kW.

    So, approximately 10.47 GW/unit.
    ------------------------------------------------------------------------------------------------------------------------------------------------

    Again, this is merely a bunch of theories and assumptions.

    I would like input on this.

    Thank you to all who gave your time.


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  3. #2  
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    Putting to one side assumptions such as "Let us safely assume that by the end of this half-century, we have organometallic solar panels capable of >90% conversion of all parts of the spectrum.", I would query the basic mode of operation of such a scheme.

    As I understand it, radiation from the sun would fall on solar panels in orbit. The electricity so produced would be converted back into electromagnetic radiation in the form of a laser beam and beamed down to earth. On arriving at the earth's surface, this electromagnetic radiation would be converted once again to electricity.

    The obvious question is, why not simply allow the radiation from the sun to fall upon the earth as it does now and thereby avoid the sending of enormous satellites and lasers into orbit?


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    Quote Originally Posted by JonG View Post
    The obvious question is, why not simply allow the radiation from the sun to fall upon the earth as it does now and thereby avoid the sending of enormous satellites and lasers into orbit?
    I would speculate:
    -Cloudy weather
    -Nighttime=downtime
    -More space in space. Why leave it at 100 square meters? Let's make it BIG.
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    The obvious question is, why not simply allow the radiation from the sun to fall upon the earth as it does now and thereby avoid the sending of enormous satellites and lasers into orbit?
    Well, the amount of radiation reaching the Earth's surface, through the atmosphere, is approximately 51% of the power available in orbit.

    Efficiency in Orbit: 76.95% (based on earlier assumptions)
    Efficiency on Surface: 45.9% (49% absorbed by atmosphere, no need for receptor and space panel)

    More importantly, any terrestrial panel is subject to performance degradation/fluctuation due to dust/rain/general weather. Given that, a panel in orbit would give much more constant output since it is not affected by any interruption.

    Most importantly, given our population's growth rate, it would (my opinion, if you've got proof against it, I may change it), be uneconomical to cover vast swathes of land in solar panels.

    Any further queries/concerns?
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    -More space in space. Why leave it at 100 square meters? Let's make it BIG.
    100x100=10k sq. metres.

    Using the same technology as solar sails, we could get panels as massive as 1 sq km.

    A part of this energy would be used by an on-board electromagnet to create a magnetic "bubble" around the satellite's electronics to prevent damage from solar winds.
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  7. #6  
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    "Well, the amount of radiation reaching the Earth's surface, through the atmosphere, is approximately 51% of the power available in orbit."


    Yes - but your laser beam also has to pass through the atmosphere, and the area over which the light would be collected by the solar panel (about 100m x 100m) is minute compared to the area of the upper atmosphere which is irradiated on a daily basis - unless you would propose filling the sky with such satellites.
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    The Amateur Calculations

    Solar Constant s=1.361 kWh/m^2
    Satellite-borne panel efficiency E1=0.9
    Transmission efficiency Et=0.95
    Receptor panel efficiency Er=0.9
    Satellite-panel area A=10, 000 m^2

    Total energy from 1 such satellite available to earth=

    s*A*E1*Et*Er=10, 472.895 kW.

    So, approximately 10.47 GW/unit.
    Again, if we use lasers, we will obviously use wavelengths that pass right through the atmosphere with minimum diffraction/scattering.

    To put things into perspective, let us say we harness x joules as visible light and x' joules as UV light in orbit.

    We then convert it into extremely-high-intensity infrared waves (not heat waves. Infrared. Heat waves are a subset of infrared waves) and beam it back.

    So we have 0.95*(0.9(x+x')) joules reaching us.

    Doing the same thing on earth gives us 0.9*(x+0.05x') joules of energy.
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    "Again, if we use lasers, we will obviously use wavelengths that pass right through the atmosphere with minimum diffraction/scattering."

    I'm afraid that you can't have it both ways. Minimum diffraction implies short wavelengths. Minimum scattering implies long wavelengths.

    "We then convert it into extremely-high-intensity infrared waves"

    I don't think this would be a good idea. The atmosphere strongly absorbs infrared radiation. The reason is quite simple - the atmosphere is made up of molecules - oxygen, nitrogen, carbon dioxide, water vapour - all these absorb infrared via molecular vibrations. If this didn't happen, there wouldn't be a "greenhouse effect". You might be able to come up with a particular infrared wavelength which would avoid these pitfalls, but could you then get a super-efficient laser to generate it? Many lasers are incredibly inefficient - but they do vary.

    What is questionable is that you appear to choose facts and figures, such as very optimistic efficiency values, to suit your purpose. I can recall a time when people thought that the answer to all energy problems would be nuclear fusion. It would be easy to set up and control, and was something just around the corner waiting to happen. That was over fifty years ago, and we are still waiting. The devil is in the detail.
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  10. #9  
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    Just out of curiousity does anyone know the theoretical limit for photo-voltaic processes based upon electron gas model?
    In the information age ignorance is a choice.
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    What is questionable is that you appear to choose facts and figures, such as very optimistic efficiency values, to suit your purpose. I can recall a time when people thought that the answer to all energy problems would be nuclear fusion. It would be easy to set up and control, and was something just around the corner waiting to happen. That was over fifty years ago, and we are still waiting. The devil is in the detail.
    We both know that no part of science can be generalized, except under laws. Keeping that in mind, I am not twisting the information/assumptions according to my needs. At 80% efficiency now, it is entire reasonable to assume that we will reach 90% or higher by 2050.

    Moving on, red light passes through the atmosphere with almost no scattering. Diffraction will not be a concern since the light will still stay in the field-of-view of the receptor panel.
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    http://www.sspi.gatech.edu/wptshinohara.pdf

    I just found a bit of information here. Keeping in mind that I'm just a 12th grader in a Third World country, can someone tell me the implications of this?
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  13. #12  
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    Quote Originally Posted by Chronum View Post
    Most importantly, given our population's growth rate, it would (my opinion, if you've got proof against it, I may change it), be uneconomical to cover vast swathes of land in solar panels.
    Population growth is expected to flatten out during this century. There are various estimates, but few if any serious ones arrive at a number much greater than ten billion. With the urbanisationprocess incomplete the issue of land space is a non-issue.

    Middle Eastern countries, currently dependent upon oil for their economy and with large tracts of unproductive desert may welcome the opportunity to emplace extensive solar generators on their territory. The lower percentage of energy reaching the surface is offset by the lower cost of installation. Repari and maintence is also orders of magnitude less expensive with ground based systtems.
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    Is it feasible to:

    1. Rely on power that has a minimum 12h/day downtime?
    2. Fill up large swathes of land with solar cells instead of terraforming them?
    3. Transmit power over tens of thousands of miles using HT wires?

    Because:

    1. Microwave transmission of power is extremely efficient.
    2. Orbital panels have no downtime.
    3. They can beam their power to different receptor stations as the planet rotates under it.
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  15. #14  
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    Quote Originally Posted by Chronum View Post
    Is it feasible to:
    1. Rely on power that has a minimum 12h/day downtime?
    If you use it as part of a total energy production, conversion and transmission solution it is wholly feasible.

    Quote Originally Posted by Chronum View Post
    Is it feasible to Fill up large swathes of land with solar cells instead of terraforming them?
    Certainly. There is no need to Terraform them, so it is entirely feasible. (I don't like your use of the term terraform in this case. Deserts are a wholly natural part of the terrestrial environment. If you do wish to 'terraform' then use some of th epower desalination and run hydroponic farm units under or adjacent to the solar cells.)

    Quote Originally Posted by Chronum View Post
    Is it feasible to transmit power over tens of thousands of miles using HT wires?
    Use the power to produce hydrogen and ship that in tankers.
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    Use the power to produce hydrogen and ship that in tankers.
    This involves physical transport of hydrogen, something which I don't think is feasible/convenient when GWs of storage is being dealt with. Why not keep the existing HT lines which we have?

    Electrolysing hydrogen out, then fuel-celling it back for power, what is the total efficiency of the process? I'm unaware. This is an honest question.

    And about your use of hydroponics, why not use them standalone?

    I'm mostly for a 'lite-mounted panel because of the downtime and atmospheric absorption. In comparison, the atmosphere is very benevolent to microwaves.

    Population stabilization, although possible, may not happen, simply due to the social scale of such a change in mindset.
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  17. #16  
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    Quote Originally Posted by Chronum View Post
    Use the power to produce hydrogen and ship that in tankers.
    This involves physical transport of hydrogen, something which I don't think is feasible/convenient when GWs of storage is being dealt with. Why not keep the existing HT lines which we have?
    There's no need to ship the Hydrogen raw. It can be further converted into Ammonia by adding Nitrogen, Methane by adding Carbon Dioxide, or Methanol also by adding Carbon Dioxide.

    In the case of Methanol, it would be burnable in ordinary automobile engines.


    Electrolysing hydrogen out, then fuel-celling it back for power, what is the total efficiency of the process? I'm unaware. This is an honest question.
    It's around 25%. So yeah, you're losing 75%, but that kind of loss is pretty common any time you're converting from one energy type to another and back again.

    And about your use of hydroponics, why not use them standalone?
    The trouble with hydroponics is that world wide, fresh water is probably even a more scarce commodity than farm land. In some regions it certainly would help. Some regions fresh water isn't scarce and farm land is I guess.

    Population stabilization, although possible, may not happen, simply due to the social scale of such a change in mindset.
    It is actually believed that this is where things are headed on their own.

    However, I think the proponents of this may be putting a little bit too much faith in that study. That's the trouble with optimism. We want to believe so badly we over-extend our faith in any good news, instead of meeting it with justified skepticism. Naturally I hope the study is right, but I try not to confuse hope and certainty.
    Some clocks are only right twice a day, but they are still right when they are right.
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  18. #17  
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    Population stabilization, although possible, may not happen, simply due to the social scale of such a change in mindset.
    The birthrate around the world is already close to 2 per woman. But this means that population will only stabilise in 30 or 40 years or so. Hans Rosling makes this simple. Hans Rosling: Religions and babies | Video on TED.com
    "Courage is what it takes to stand up and speak; courage is also what it takes to sit down and listen." Winston Churchill
    "nature is like a game of Jenga; you never know which brick you pull out will cause the whole stack to collapse" Lucy Cooke
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