Alternative Way to Harness Solar Energy

Discussion in 'General Science & Technology' started by hayenmill, Jun 19, 2009.

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  1. hayenmill Registered Member

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    SOLAR POWERED STIRLING ENGINE:

    (again, can't post any links yet, delete spaces between http): h t t p ://digg.com/d1rmzX

    It also links to various websites where they show you how to make one from simple household items

    thoughts?
     
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  3. error01120524 Registered Member

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    So you would like to harness the sun's energy for means of transportation, why? There has to be a better energy source for that purpose.

    I would use solar energy to give power to our cities, the device to transform the solar energy into another usefull type of energy wouldn't have to be mobile (as in need to move, like a car).
     
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  5. ElectricFetus Sanity going, going, gone Valued Senior Member

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    In theory storing solar energy in batteries of some kind of chemical from can power transit. And yes I relies the irony of us using stored solar energy at present, but we need to start storing it our selves and with greater efficiency then how it was done naturally.
     
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  7. hypewaders Save Changes Registered Senior Member

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    There are many advantages. First and foremost, evacuated-tube Solar-thermal collecters are fuller spectrum than PV, and extract far more energy from both direct and diffuse (cloudy-day) light. The technology is more basic than PV, allowing common mechanical and plumbing skills/materials to produce practical systems.

    On the down side, Solar-thermal/mechanical generation requires more maintenance, and involves additional conversions of energy (radiation-therm-mechanical-electrical) which means loss. PV bypasses those steps.

    As a solar power installer, I've been lamenting it for years that solar-thermal to electric hasn't been developed. But it's surely coming.

    An earlier thread: Stirling Energy Conversions
     
  8. DRZion Theoretical Experimentalist Valued Senior Member

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    Isn't all energy on earth technically 'solar'?



    With stirling engines, isn't the highest cost component the actual engine? Harnessing multiple collector mirrors at once could be very cost effective..

    In this case one could just put a photovoltaic cell at the focal point of the mirrors, or are the high temperatures not suitable for pvs?
    :shrug:
     
  9. ElectricFetus Sanity going, going, gone Valued Senior Member

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    There is the idea of having solar thermal tubes lined with PV, thus they double duty, but I really like the idea of having a solar thermal system with a stilling generator in the basement, when you don't need hot water it can go to powering the generator.

    Almost all energy on earth has come from the sun, exceptions are nuclear and geothermal.

    No there not, PV need lower temperatures to be efficient.
     
    Last edited: Jun 20, 2009
  10. DRZion Theoretical Experimentalist Valued Senior Member

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    Nuclear and geothermal are partially linked, since the core is heated through radioactive decay.

    "a solar thermal system with a stilling generator in the basement, when you don't need hot water it can go to powering the generator"
    the problem with this approach is that modern sterling engines require considerable temperature differences to be efficient.
     
  11. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Go to: http://patft.uspto.gov/netahtml/PTO/srchnum.htm and enter 4033118 to see my long expired patent. It solves the fundamental problem of Solar Thermal Power, which is:

    For good conversion efficiency a high absorber temperature is required; but re-radiation losses from the absorber increase as the fourth power of the absolute temperature.

    Patent shows how to have coefficient of absorption, a = 1 as the “absorber” is just the open hole in the end of a glass cylindrical “mirror tube” (Reflective surface is on the outside of the tube.) That entrence end of the mirror tube remains near ambient temperature as only ~4% of the incident flux is absorbed with the first wall reflection and ~96% reflects deeper into the tube.

    A second larger tube, concentric with the mirror tube forms an annulus in which the working fluid flows. It enters at the concentrated sunlight end relatively cool and absorbs the 4% of the heat produced by the solar flux in the first section of the mirror tube.

    As the working fluid travel along the outside of the mirror tube it becomes hotter and the intensity of the solar flux inside the mirror tube decrease with each reflection as both sunlight and working fluid travel further from the entrance. Slowly the glass grades into quartz to have the needed strength. (Glass would melt as the temperature increases far from the entrance.) Far from the entrance the interior is filled with intense black body radiation, IR.

    This IR tries to mirror back out and escape but as it travels back towards the entrance, it increasing is re absorbed by the glass/quartz blend walls and these less distant walls are at a lower temperature. When the lower temperature IR reaches the glass only walls, nearer to the entrance it is complete absorbed in the walls – cannot “see” thru the glass to reflect on the reflective layer and continuing mirroring back towards the entrance. That is, if there is a slight bend in the mirror tube to eliminate the direct escape path to the entrance, then essentially to re-radiation losses are reduced to zero. The IR does add to the thermal loading on the walls. I.e. The IR trying to escape is re absorbed and the glass wall near the entrance where it could escape from are keep cool by the entering working fluid.

    The calculation of the solar and IR flux on the walls as a function of the distance from the entrance is presented in two separate papers published in Applied Optics more than 35 years ago – exact reference is give in the patent.

    My recognition and solution of the fundamental problem limit the conversion efficiency of Solar Power was too early to be profitable to me as then oil was in the $10/ barrel price range or less and few were concerned about “peak oil” etc. The fundamental problem is now solved, and largely forgotten. Now the temperature is limited by the softening point of quartz –

    For obvious reasons, the title of my inventions is: Mass flow Solar Absorber.

    SUMMARY: a unity absorption coefficient absorber can be “red hot” and yet have essentially zero re-radiation losses.
    This permits much greater conversion efficiency as that is limited by the Carnot cycle to (1 – t/T) where T is the high temperature of the heat source and t is the colder temperature the waste heat is rejected at.

    The patent also describes how to chemically store the energy via the reversible reaction:
    2SO3 <----> 2 SO2 + O2

    I.e. when sunlight is available in excess of power requirements, O2 and SO2 are produced by the thermal decomposition of SO3. When heat is wanted from the stored (compressed in tanks) O2 and the easily liquefied SO2, one re-oxidizes the SO2 with the stored O2. I.e. In this case, the "working fluid" is SO3 in a closed, reversible-cycle, storage system, but others are also possible. This one just seemed the most attractive to me long ago.

    If the electrical load needs the full solar energy available, the hot SO3 + SO2 + O2 mix exiting from deep end of the mirror tube is expaned thru a turbine and when cooler returned to the entrance end of the annulus surounding the mirror tube - also a closed power cycle. During this expansion much of the SO2 and O2 will combined (like burning fuel in the turbine) and mainly SO3 will exit the turbine, but it will need to be compressed up to slightly above the entrance presure of the turbine. I have never worked these considerations out in detail as they are not the essence of the invention and Physical Chemistry is not my field.
     
  12. error01120524 Registered Member

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    20
    While we are talking about solar energy, I have a question, it may not necessarily related to what you guys were talking about.

    So here's my premise, light is an electromagnetic wave. Light has a wavelenght and frequency. Now lets go back to the radio. The radio stations send out radio waves wich we receive by means of a radio, we do that every day. Now lets look at what happens in a bit more detail: the radio waves sent out arrive at an antena, which is then excited (there's a current going through it). Then this current is decoded by the radio as sound. We tune the radio to different frequencies by means of an RLC circuit. That's basically how it works. Suppose we do Hertz's experiment all over again, except instead of "listening to the radio" we use the receiving current as "usefull" current, i.e. light a lightbulb. This experiment is just to know how much energy is lost between the transmission and reception of the radio wave. Suppose we use X Joules in the transmission device and we can extract Y Joules with the receiving device (X >>> Y, most probably), let's say we receive 0,1% of the energy transmitted. We know that radio waves are electromagnetic waves and visible light is an electromagnetic wave too. Suppose we can do the same thing we did with radiowaves but with light, couldn't we have energy until the transmiter (aka the sun) turned off. Now we know that the sun emits megaJoules of energy per second as light, 0,1% of a megaJoule is still pretty big. The question is would it be possible? I don't exactly know how antenas actually receive the EM wave, but the only problem I would see is that it's not as simple as it may sound to "receive" light.
     
  13. DRZion Theoretical Experimentalist Valued Senior Member

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    error, is this what you mean?
    https://inlportal.inl.gov/portal/server.pt?open=514&objID=1555&mode=2&featurestory=DA_144483

    It could be theoretically far more efficient to use tiny antennas to receives sunlight than photovoltaics. Novack claims 80% efficiency, but I haven't read the paper and I'm not exactly sure how this works.

    Visible waves are very, very small and so one would need to use billions of nano-antennas in a carpet [much like a photovoltaic cell] to harvest this energy. Radio waves however, are tens or even hundreds of meters in length, and so one can use macroscopic masts to convert them to electricity.


    Billy, I'm still reading the patent. This does give me an idea though - one could make a mirror for infrared invention out of a material that transmits visible radiation. This way when the object heats up due to thermal radiation it cannot emit this radiation, up to a certain temperature.
     
  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes. That works for small power levels, but not for anything of comercial interest. In fact I became interested in the subject because some were trying to make and use a selective filter sort of as you suggest. - Let the sunlght thur to the absorber but reflect the absorber's IR back to the absorber.

    There are two ways (extermes) to do this. Coat the primary mirrors with a selective film, and that would work, but increases the cost of the mirrors at least and order of magnitude. - Is not economically feasible, especially as much of the re-radiation IR would not even fall on them.

    The alternative is to place the selective filter in the concentrated sunlight path. Then it can be a much smaller area and not too expensive to consider. Unfortunately, all attemps to do this failed. The filter is not perfectly transparent to the sunlight and gets very hot. - Is rapidly destroyed by thermal diffsion. Also if it is very hot a sudden rain can fracture it. (Rain can be local with sunlight very concentrated on it.) There is also the "bird shit" problem -area where that is has zero transmission so is much hotter and differential thermal expansion can crack it.

    This also a seldom discussed problem with a series string of solar cells. (Higher votage of a series string is desirable as then less loss in the fine collector wires.) If one cell is in the dark because it is covered by B.S., it has high resistance and the others in the string drive current thru it, so can destroy it thermally. This makes the string open circuit and usless til it is replaced. Maintaining a commercial scale field of PV cells is more costly than most like to think. Thus I think Wind power is much more practical for comercial market than PV cells and it usually continues after sun set. I think (and have read) that the cost of PV cell power is less than 5O% the capital cost of the solar cells - even if they were free, commercial solar power can not compete with a coal-fired grid power economically.

    But your thought is a good one.

    Another idea that also works in principle, perhaps even in practice, but AFAIK has never been attempted is to line the INSIDE of most of a shere with PV cells, leaving only a cone with apex that the center of the sphere open for concentrated sunlight to fall on an absorber there at the center.

    This absorber gets very hot and radiates more useful IR photons than the flux of solar photon entering the sphere as the wavelength match of the IR radiation is a better fit with the band gap of the PV cells. Each solar photon can make only one electron jump up to the conduction band. - Thus at least 78% of the solar flux at the Earth's surface on clear day noon is degraded into heat with simple silicon PV cells. - Even if the solar photon has twice the band gap energy, you can only get the band gap energy and some are too long a wavelength to make anything but heat.

    This is hot local radiator is a "photon multiplier" idea. Silicon PV cells would be more efficient it our sun were a cooler "red giant."

    The best solar energy is a hydroelectic dam. Brazil gets 70% of its electric power from them and another 5% from burning the crushed sugar cane* and a growing percent from wind power. Soon Brazil will be 85% solar electric power and it cars already are about that as they run on sugar cane alcohol.

    -----------
    *On an annual basis, more during late summer and fall. - Well matched to the peak demand. (The crushed cane can be stored too, but seldom is.)
     
    Last edited by a moderator: Jun 22, 2009
  15. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Error
    In additon to DRZion's link (2009 effort) there were very serious suggestion of doing this in space. Where solar energy is available 24/7 and more intense. The energy collected (even by thermal converison* or PV cells) is then converted to micro waves, which are resonate with the earth based rectena array. The military was interested also - a "death ray" cooks your enemy, but that was 25 or more years ago an I have not heard much of it sense.

    Also read about Nicoli Tessla - he actually tried to distribute electic energy without wires. How much he succeeded is debatable. He invented AC and Edison stubbornly stuck with DC as he did not understand how an AC motor could work.
    ------------------
    * The back side of the collecting mirror looks out on a very cold radiator (deep space) - very high Carnot efficiency possible in principle.
     
    Last edited by a moderator: Jun 22, 2009
  16. DRZion Theoretical Experimentalist Valued Senior Member

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    Here is another interesting idea harnessing solar energy-
    http://en.wikipedia.org/wiki/Solar_updraft_tower
    This could potentially harness solar energy only using plastic foil, connected to a wind turbine. I do not understand why the chimney should be so tall, it seems to only be a method of increasing potential energy. It does increase pressure, and perhaps this adds to turbine efficiency.

    Billy,
    This 'selective radiation' can be achieved using photonic crystal paints, as well as some very selective materials. Photonic crystals act as mirrors for certain wavelengths and are absorptive or transparent to others.
     
  17. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    You sort of have it. Sytem works only due to fact the presure at base of a tall contained column of warm air is less than that of the outside air. Thus, taller generates more pressure difference. Also there is a general tendency for the "outside" air temperature to drop (roughly adibatically) with elevation. the air inside & outside near top of the tower are not a dense as at the bottom (which is compressed by the weight of the air above), but the external being colder makes the density outside greater.

    Do you have link on them? If applied to the absorber you want solar a near 1 and IR a near zero (good IR reflector) I doubt that these paints will take the high temperatures desired in the absorber.
     
  18. DRZion Theoretical Experimentalist Valued Senior Member

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    1,046
    This is the logic-
    A mirror, 99% reflective for a certain frequency in the IR. A material that reflects 99% has a low absorptivity, right? So, it has low emissivity.

    Here is a link on photonic crystals- http://www.laserfocusworld.com/articles/349359
     
  19. riverline Registered Senior Member

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    103
    no matter how effeciently you store solar energy, you can not harvest energy from the sun more than it gives earth. the daily solar energy received by earth is half the global daily enegy consumption of oil .
     
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    That very false, so would like to see your claim support instead of your ignorant BS.

    “Here the desserts of the earth can play a role. They receive about 700 times more energy from the sun than mankind consumes by burning fossil fuels, day by day. …” {that is only the deserts!}

    This quote is from crown prince of Jordan in his introduction to a 60 page “white paper” by dozens of different energy experts, many with Ph.D.s, called: “Clean power from the deserts”

    It is filled with so much accurate and valuable information that I stored it in my computer (as .pdf file) but now have lost the link; however, here is a "start page" to dozens of related pages: http://www.desertec.org/
    Also See DEASERTEC(summary) at http://www.desertec.org/downloads/summary_en.pdf

    Several European countries in the last month or so have formed a union to finance the use of the Sahara Desert to escape from total dependence on Russia for their energy. Here is a shorter link discussion this starting to be real (early phase funded) plan:
    http://www.solarserver.de/solarmagazin/solar-report_0207_e.html
     
    Last edited by a moderator: Jul 23, 2009
  21. iceaura Valued Senior Member

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    An area of Southwestern US desert 100 miles on a side, solar harvested year round at currently available efficiencies (stirling engine thermal collection and electricity conversion right now runs easily at 40%, sophisticated at 60%, laboratory over 90%, or about triple any reasonably likely PV in the pipeline) could in theory replace all other sources of power in the US.

    Distribution and storage being solved.
     
  22. quadraphonics Bloodthirsty Barbarian Valued Senior Member

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    People much more informed than I am tell me that distribution and storage is actually the primary barrier to most renewable/green energy plans, both in terms of costs and technology. But this doesn't get much attention, since it's not a sexy issue, and is largely considered "solved" by most laypeople.

    The thing about fossil power generation is that you can just crank up the gas during times of high demand, and turn it back down when demand falls, and so our storage and distribution infrastructure reflects this. The sun, wind, tides, etc. are not nearly so accomodating, however, and so we need all kinds of improvements and redesigns, many of them systemic.

    Supposedly the really smart money is in figuring this stuff out. If somebody can come up with a grid technology that can actually take advantage of these alternative power sources on a national scale, the wind and solar farms will all fall into place and they'll have more licensing revenue than they'll know what to do with.
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    To Quad:

    Your post 19 is 100% correct. I have made the same point as follows:

    Intermittent solar energy (in direct form never there at night, and even wind greatly reduced in strength just before dawn) needs some combo of storage or "back up." While only a few are trying to run their homes on mainly solar power, they can avoid all the cost of storage and dump the excess power into the power grid (run their electric meter backwards) for free. They add to the peak power demand and the capital required to finance generation and distrubution, but use little net energy and that is what the simple meter charge is based on. (Meters that separately measure and record peak demand are more expensive and only currently installed for industy.)

    The dumb masses are paying for their storage, but a the masses are many and the fully solar homes are very few - the cost of storge they are avoiding does not yet produce any revolution in the charging to make them pay their fair share of the cost. The masses will not continue to be exploited by the few when they be come more numerious and the cost transfered to the non-solar masses is noticed by them.

    Because storage is very costly (at least 80% of your electric bill is paying for the capital cost, not the fuel, which cost ZERO if it is hydro-power and essentially zero if it is nuclear power.) I would guess "free" grid storage for solar homes will never get to be enjoyed by even 5% of the homes.

    The masses are less dumb when you reach your hand into their pocket than about any other time. (Especailly true in this case, as only the rich can afford the high capital cost of the solar home. There is a lot of "political hay" to be made by pointing out to the masses how: "Once again the rich are exploiting you." Probably because of this political consideration, even 1% solar homes will cause them to pay for the extra cost they cause but currently do not pay.) I have a central solar thermal power patent, long expired, which I think will be the way mankind eventually gets much of his electric power that is not nuclear. Thus, I favor central, not roof top, solar. Perhaps I will run for office on the "Don't let the rich screw you again as we go green" platform.

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    Last edited by a moderator: Jul 24, 2009
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