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By Dan
#8373
Have you ever played in the sun with a magnifying glass? Even the smallest ones can burn wood, or set grass on fire.

So, why can't we build a manifying glass array, point that sun heat towards a steam turbine and produce electricity? Steam turbines are readily available as are the generators they drive. The major engineering would be setting up the glass array and building a solar tracking system to keep it aligned at the correct angle to the sun.

Reward: My reward would be a big smile knowing we are finally using something else besides oil, gas or nuclear.
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By Steve
#8411
That's actually exactly what solar cells are doing - only on a more abstract and more efficient level.
By shari
#8421
What is proposed may not be the same as solar cells - solar cells are normally photo-voltaic cells and generate DC power using photodiodes.. This is like a solar heat powered steam turbines which can generate electricity, where the electricity generated would be AC. I guess this might be limited to generating power on a large scale, whereas solar cells can be deployed anywhere. But this could be a good source of alternate fuel for thermal generators.
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By Steve
#8422
Ok then maybe it's not what solar cells are doing. O:-) Something in my left arm still tells me that this isn't an efficient way to produce energy, but what does my left arm know? :-? Maybe it's the size of lens you would need to get this running (associated with the costs). Let's say you have a 10m lens (in diameter) to heat a 10m tank of water. Wouldn't it be the same to omit the lens and have the sun shine on the tank directly?
By old_kyle_w
#8758
I think the idea is a good one, especially for areas that receive full sun on a majority of days. It might be a bit more cost effective to build concave mirrors to focus the sun rather than lenses (it would depend on what materials you selected which would cost less). Just my two cents.
By Willlxx
#8771
I have never been able to understand why using concave lenses in conjunction with solar cells doesn;t make them more efficient and if they would why banks of lenses couldn't be used to focus a wide range of light into a small area?
By Rishi
#8775
A whole lot of work has been done on this. One does not really need any lens or mirror to collect the solar energy. A plain flat mirror will do. The catch as always with alternate energy is the cost.

The solar radiation on a clear day will be about 0.8 KW/sq.metre in the tropics at near noon. It will be about 0.5KW/Sq.Metre in the temperate zone. With reasonably good tracking it will be possible to get 3 to 3.5 KWHr/sq.metre in the tropics between 9 AM and 3 PM,the period of best collection at good power levels.

What has been tried so far is to align a large number of flat mirrors to point to the surface of a boiler mounted on a tower. The boiler is inside a vacuum chamber and coated with a special coating which has a very high absorptivity and very low emissivity(To maximise collection and minimise reradiation). The generated steam drives a turbine. Either AC or DC can be produced.

Each mirror has a miniature motor, which tracks the sun(Of course, consuming some power) much like the motors that automatically track stars with telescopes.

It is best to have mirrors arranged in a circular disposition around the boiler tower, to ensure a reasonably constant collection through the day. (One half will be active more in the forenoon, the other in the afternoon. Usually a central computer controls all trackers, though stand alone cheaper trackers have been studied.

In addition to the huge capital cost, a very large clear area with no obstructing buildings (at the time of setting up and forever theafter) is needed. The mirrors have to be kept clean at all times (Difficult with all kinds of weather).

It is obvious that all this will cost a packet. An ingeneous mechanism using a bimetallic element coupled with a shadow screen has been developed by some MIT (USA) group (about twenty years back) to trck the sun without any motor. This group has also made a hotplate for domestic application using the latent heat of molten Sodium Nitrate. A parabolic cylindrical mirror using this kind of tracker was used to melt the sodium nitrate.

The idea is very welcome and proved in actual trials. Turbines using acetone and other low boiling liquids are also reported.
The (literally) billion dollar question is: Can we afford it?

rishi
By OCTOMAN80@MAC.COM
#15981
HI DAN: I HAVE A N OCTAGON HOME WITH A SKYLIGHT IN THE CENTER OF A 12' OCTAGON UTILITY ROOM. MY DREAN IS A NEAR ZERO HOME WITH NO ROOF OR YARD GARBAGE. I HAVE THIS MODELED TO ACHIEVE NEAR ZERO WITH NO ATTACHMENT TO THE ELECTRICAL GRID. I WANT TO PUT THE FROSTING ON THE CAKE WITH AN ARRAY OF MAGNIFYING GLASSES ARRANGED ON AN ARC BAND SHAPED TO THE PARTICULAR LATITUDE AND HINGED TO PIVOT, FOLLOWING THE SUNS MOVEMENT FROM NORTH TO SOUTH. THIS WOULD HEAT WATER OR GENERATE STEAM IN AN INSULATED TANK IN THE CENTER OF THE UTILITY ROOM.. I WELCOME SOLUTIONS. I AM BUILDING THIS HOME NOW. TIME IS OF THE ESSENCE. I AM A SERVANT OF MANKIND & WISH TO SHARE IDEAS.

CURTIS L. BIGGAR, ARCHITECT
By changer1
#19792
curtis

I have kicked this idea around for 25 years. 1. who manuractures magnifine glass, My spelling is crap. 2.tracking systens, I know there are computer programs that do this , don't know where. 3. I have had an experiance with a type of wood stain that if the rags are kept in the sun they spontainisly combust. my question is if a radiator is filled with the cemacel in the stain that atavates combustion is kept under control how could this not amplify the suns effects. 4. there is no way passave solor is equivalent to foucasing the sun. With shanges in house desine like what you are doing and a 6 foot glass foucesed on a steem generator every home could be self safisent. A home product not a huge new national of world grid is the way to prosead.
John off to work
By Rishi
#19793
changer1 wrote:curtis

I have kicked this idea around for 25 years. 1. who manuractures magnifine glass, My spelling is crap. 2.tracking systens, I know there are computer programs that do this , don't know where. 3. I have had an experiance with a type of wood stain that if the rags are kept in the sun they spontainisly combust. my question is if a radiator is filled with the cemacel in the stain that atavates combustion is kept under control how could this not amplify the suns effects. 4. there is no way passave solor is equivalent to foucasing the sun. With shanges in house desine like what you are doing and a 6 foot glass foucesed on a steem generator every home could be self safisent. A home product not a huge new national of world grid is the way to prosead.
John off to work

IChanger1, It is not that simple.
When a solvent soaked rag burns, it is the rag that is the fuel giving energy not the sun. When a trigger is pulled it is the gun powder that propels the bullet not the cap that sets off the powder. You cannot get more energy than coming in per square foot of solar collector by using a concentrator. You can only increase the temperature. A 6'x6' lens focussing on a steam generator driving a turbine may generate at the most 3 to 4 KWHr of energy in the temperate zone.
Rishi
By Killrb64
#19945
Rishi wrote: You cannot get more energy than coming in per square foot of solar collector by using a concentrator. You can only increase the temperature. A 6'x6' lens focusing on a steam generator driving a turbine may generate at the most 3 to 4 KWHr of energy in the temperate zone.
Rishi


What is the energy consumption of an average home?
By changer1
#19946
I still don't buy foucesing the sun to a spot is the same as passavily colecting sun rays. Risisi you missed the hole poin of what was happening with the solvint. Yes the rag burned , my poit is the solvent by its self mutaplyed the suns effects on the rag. How much power dose a home use?
I had alwayshoped that house by house solar generators would go up like the satalite dishes did. there is always something better we just need something that works.
By Killrb64
#19947
changer1 wrote:I still don't buy focusing the sun to a spot is the same as passively collecting sun rays. Risisi you missed the whole point of what was happening with the solvent. Yes the rag burned , my point is the solvent by its self multiplied the suns effects on the rag. How much power does a home use?
I had always hoped that house by house solar generators would go up like the satellite dishes did. there is always something better we just need something that works.


No, Changer, YOU missed the point. The rag and solvent ignited and burned. They are not multiplying anything, they are burning,(as in fire ), like wood or gas or propane.
Rishis point about focusing or not is that only a certain amount of energy is falling on a given area, whether it's all over that area or concentrated in one spot by a concave mirror or lens.

And also. when the red line comes on after you type a word, that means you're doing it wrong.
Right click on it and you will be shown the several choices of what the computer thinks you're trying to spell. You should really get to know this feature. ;D
By ABBG
#20045
I have recently watched a "Tomorrows World" type of program on TV with James May showing some of the research on this subject that is currently being conducted in a desert area of I think Spain.
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