h a l f b a k e r yAssume a hemispherical cow.
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Solar energy is a very promising
technology for replacing fossil fuels. The
amount of solar energy that hits the
earth
greatly exceeds our total energy needs.
However, even though we need energy at
night, solar energy does not work at
night.
To solve this problem, we could build
giant
batteries. However, large-scale
energy storage is still very immature. But
due to the rotation of the earth, part of
the earth's surface is always lit and part
of
it is always in darkness. Therefore, if
solar
plants were built in only three areas in
the
world near the equator, the Nevada
Desert
in the US, the Sahara Desert in Africa and
the deserts in Australia, then one or two
of those plants would always be in
daylight and producing energy at any one
time. If we could connect these grids
together, we could power the entire earth
continuously.
To do so, we would need to build large-
scale underwater power cables. These
would connect each continent together,
allowing excess energy from sunny parts
of the world to be sent to areas of the
world which are in darkness. They would
also connect areas which are suitable for
solar power (near the equator) to areas
near the poles where solar power is less
efficient. They would be laid in a manner
very similar to that of transoceanic fibre
optic cables. The technology needed to
build high-voltage underwater electrical
cables exists, but it hasn't been used for
projects of this scale.
This technology could equally be used
for
redistributing energy made from other
sources which produce a constant output
(hydro, nuclear, fossil fuels, etc.),
because
demand for electricity varies by hour
(peaking in the evening and reaching a
low late at night).
The Green Line
http://www.boston.c...green_power_to_hub/
[ldischler, Feb 10 2008]
PRESENT LIMITS OF VERY LONG DISTANCE TRANSMISSION SYSTEMS
http://www.geni.org...systems/index.shtml
[ldischler, Feb 10 2008]
NorNed power link
http://library.abb....r,%20Norned_low.pdf
The current record holder for undersea transmission length [lurch, Feb 11 2008]
Electrical frequency
http://en.wikipedia...y_frequency#History
Why 50Hz or 60Hz etc. [Ling, Feb 12 2008]
Energon
http://en.wikipedia..._%28power_source%29
Energon ore is a glowing, golden yellow in colour [ed, Feb 15 2008]
So Cal Solar Farm
http://www.reuters....eedType=RSS&sp=true
[doctorremulac3, Feb 15 2008]
Solar parking lot
http://www.wired.co.../news/2006/12/72292
[doctorremulac3, Feb 15 2008]
[link]
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I like the principle. [+] In practice (correct me if I am wrong), but doesn't the resistance in a power cable increase proportionally with the length of the cable and the power that gets put through? Might not be practical. |
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Perhaps you could transport the energy another way. |
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The resistance makes this futile. |
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AFAIK, the most efficient way of storing energy is to pump water into a lake on a hill. Hmm, perhaps blowing up a big balloon on the sea bed might work too. Cracking water is another option. |
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So, crack water using solar power and pump the hydrogen into a big underwater balloon for storage. Reclaim energy from the pressure as it comes back up, burn it at the top of a hill, and then get more power as the water goes back downhill to your cracking plant. |
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Disclaimer: I am not suggesting that this would be a perpetual motion system. |
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Use the power locally to electrolyse seawater, then transport the hydrogen to where it is needed, a little like the proposed Icelandic scheme.
//areas in the world near the equator, the Nevada Desert in the US//
I'm guessing you're not a geographer, [andrewm] |
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This is one of those things that are obvious but unworkable. If electrical power could be carried long distances, we'd be doing it already. |
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I didn't know that the Nevada Desert was all that near the equator. |
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Furthermore the cable represents a choke point that would be vulnerable to natural disasters, international incident, and terrorism. Depending on a power system that is not robust or repairable spells disaster. |
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Resistance is proportional to the reluctance of the material, the distance conducted, and inversely proportional to the cross sectional area of the conductor. |
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Resistive losses are proportional to the current carried and the resistance of the conductor. That's why long distance electricity is transferred via high voltage/low current. It's also why earth-returns work, because the cross-sectional area of the earth is pretty darned big, and earth-returns can have resistance in the milliohms range. |
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More to the point, I'm not sure where the //the most efficient way of storing energy is to pump water into a lake on a hill// bit comes from. Pumps and turbines aren't really that efficient. Electrolysis and hydrogen burning/fuel cells aren't all that good either - whole system is generally <50% efficient. |
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Let's just say I expect to see transoceanic power cables before I see space elevators. |
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[Custardguts] I didn't say they were efficient, I said MOST efficient. Perhaps if I'd have said least wasteful it would have been clearer. Do you know of a more efficient way? |
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I think cables over 1000km will have to wait until someone manages to make production of nanotube wire cheap enough. They have extremely low resistance. |
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I thought that skin effect was only significant at higher frequencies, ie >> 50 or 60Hz ? |
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The major problem here is that the cable is underwater. While in an air environment, you can go two or three thousand klicks, underwater the max for AC is 60-100 km. The new "NorNed" system is HVDC, 580 km from Norway to the Netherlands. They're claiming about 4% losses. (Dual core cable, 790mm^2 copper, 100mm separation - very low external field generated. They're not designing for skin effect.)
(BTW - that cable is 90kg/m - yowza!) |
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//I said MOST efficient// .. And I said you were wrong. The very best you'll get out of a pumped water system is ~75%, and they are by nature permanent, static systems. |
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//Do you know of a more efficient way// Battery storage can easily beat 75% recovery. For static systems, pumped water is more economically efficient, just not on a per-joule basis. Hell, a flywhweel system can beat 75%. |
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Regardless, at 4 <edit>% losses for 580km, you can transmit for about 3600km before you hit 25% loss. And other factors come into play at that range, 25% is a lot to play with. I'm really curious whether it's more efficient with HVDC to use earth-return and utilise the conductor savings (only have to run one cable) to up your conductor size. I can't imagine it isn't, as long as you can get a good earth. |
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//Regardless, at 8% losses for 580km, you can transmit for about 3600km before you hit 25% loss.//
That would be more like 40%. |
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If you had superefficient long distance power transmission, the South Africans could become fabulously wealthy by building an enormous number of nuclear power plants and powering the world. Forget solar. Nukes nukes nukes! Nukey Nukey Nukes! |
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Ok, I concede. I guess the reason they use lakes is more to do with set up costs than running losses. |
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[Custardguts] - from what I've been able to find, undersea earth-return systems encounter a rather interesting problem: they generate chlorine. |
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//Nukes nukes nukes! Nukey Nukey Nukes!// |
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The UK nuclear lobby has been campaigning much along these lines for many decades now. |
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//Do you have an authoritative source for that 40% claim, [ldischler]?//
(1 - 0.08) ^ (3600 / 580) = 0.59. ?
No? |
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[lurch] thanks. Gee, I wouldn't have thought you'd be making chlorine unless one of the earthing points was immersed in the seawater. I'm guessing from your anno that there must be some kind of leak current along the length of the cable, and you get distributed chlorine production for the whole cable. Or something. |
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Wow. I would have thought you could get past that by upping the insulation on the conductor. |
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Isn't this a "Do X, only bigger"? |
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However, some interesting comments. |
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Skin effect also occurs with high current dc, as I recall. |
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I read in some some book, probably by Laithwaite, that low frequency transmission was not used in the UK with a mind to transmission losses. At that time, power stations were local to point of use. Transformers, if used, would have been very large. Traction applications worked better at low frequencies (trams etc.) |
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Frequency selection was rather arbitrary in the past, within mechanical limits. |
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From what I've been able to find, it appears that the production of chlorine in seawater is largely, but not totally, influenced by the environmental attitude of the researcher. ;) |
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Seawater makes such a good return path that the cathode and anode earthing points are placed in the water. This eliminates some of the problems of having the connection on land: the need to keep the ground wet, the steep voltage differential in areas near the connection, ground prep & excavation, and cost of real estate.
Using the Germany-Sweden Baltic cable as an example, titanium mesh is placed underwater for the anode end, and the cathode end is constructed of copper cables. The figures quoted by ABB Power Systems say that the chlorine reacts with water to make hypochlorous acid - a weak acid that does not dissociate easily in water - and that the resulting hypochlorite concentration is only about 1% that of chlorinated drinking water. |
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I generally find myself toward the opposite end of the spectrum from the environmentalists, but here I have to wonder - how much of the evolved chlorine gas escapes into the atmosphere? That would lead to an imbalance of sodium in the seawater, which would tend to create an alkaline environment. |
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Anyway, that all goes away if you use a bipole; plus the two wire system can use smaller cables. A single wire system has a set voltage on the wire, and the return is at 0 volts ground reference. A two wire system can have equal but opposite voltages on the two wires, doubling the delivered power for the same amperage. Another interesting side-effect of a bipole system is that if one of your cables gets cut, you can instantly switch to earth return and instead of failing completely, still run the link at half power. |
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Yeah, [UB], dc is about as low as it goes. |
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(later, link: frequencies). All sorts were used in the past. "Low" good for motors, and "high" good for lighting and small transformers. |
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Like everybody's said here, transmission loss is the killer. |
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I think there are two ways to best utilize solar power: |
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1- In sunny areas, cover building's parking lots with solar panels. Acres of solar panels could be put up easily, very close to the buildings they're servicing. Cars would be shaded and covered from the rain and transmission loss would be almost non-existent. Parking lots are also sized proportionally to the buildings they service already so they're ready made. |
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2- In large urban areas in the sun belt that are adjacent to largely un-developed desert areas, build large solar farms outside the city designed specifically to cover the peak power load on the hottest days. I would actually have the solar panel factory on site and put out a couple of thousand square feet of solar panels a day. Los Angeles would be perfect for this. Big ever expanding solar farm out in the desert, you're all set. |
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The parking lots have been done with great success I understand. I think it just needs to catch on. |
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Peak load solar farms and parking lot solar panels. |
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//At one time the British were using 8Hz, as I recall.//
That would surprise me. 87 Hz was used in the city of Coventry. I have a listing of the voltages and frequencies historically used by various authorities; I'll check when I get home. |
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Piping liquid Energon would be the best solution; no transmission loss. (see link) |
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How well would microwave waveguides do on extremely long distance power transmission? I assume they would be extremely expensive to build, but if they are experimenting with sending power from space with microwaves, the efficiencies would have to be WAY better in an enclosed wave guide. |
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IF I were going to use sunlight to create large energy distribution systems, I would do it another way. Let us suppose we had a gigantic solar energy farm, much like the one they are building in southern California right now...that takes up 4500 acres and is supposed to provide power to 230 thousand homes...We build the plants in dessert or off shore sunny locations near the equator...but, instead of trying to cram the power into long resistant power cables, we use it to break down the water molecules into hydrogen and oxygen. We then release the oxygen into the atmosphere and liquify and bottle the hydrogen, put it on ships and send the hydrogen fuel around the world, selling it much as we do crude oil today. It would not matter if the hydrogen was burned in power plants to provide home with electricity or in cars for transportation. These mega-energy plants would generate very little pollution, the fuel would recombine with the released oxygen when it is burned, no matter where, and produce pure water vapor into the atmosphere as an added help replacing the water that had been cracked in the original production process. |
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I doubt the carbon would react with the O2 any more than it already does with the abundance of ready made, natural O2...but think of the carbon being deliberately kept from reacting, trillions of gallons daily of hydrocarbons no longer being burned. Incidental reactions, as in ground bacteria, plant decay, and forest fires and brush fires, sure...but, that goes on anyway....with or without human beings. |
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