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SJorgensen
05-16-2006, 02:27 AM
I've been thinking about alternative energy. I realize that almost any alternative energy plan will be criticized as "crazy" and it has been proved so many times. The oil industry can lower the cost of fuel drastically and low enough to crush competion, and they have done so many times.

Here is an idea that I've been playing with. It is for a solar steam generator on the cheap. Long frames would be set up in an East/West orientation. Long sheets of clear and thin plastic would be held in these frames and water would be on top of the plastic. The plastic would deform in a parabolic shape by the weight of the water in its cross section. Another sheet of plastic might be required on top to prevent wind from reducing the focusing effect of the water on these channels of water. I've been thinking scales of 1 foot wide and 3 foot wide but I haven't experimented.

These long frames of plastic would effectively become lenses that would heat water contained in tubes underneath the frames at the focal point. The goal would be to have the tubes underneath reach temperatures higher than 212 degrees and to generate a working steam pressure. These panels could be on roof tops or on open land.

There are certain problems with the introduction of the water in the tubes and the handling of the steam pressure, but I think it could work. It wouldn't cost very much to set up. Certain modifications would be required to avoid "slugging."

Evan
05-16-2006, 03:08 AM
Sorry to burst your bubble but it isn't feasible for one simple reason. Water is nearly opaque at deep red frequencies and near infrared as well as ultraviolet and above. That is why water looks blue. It transmits almost no heat.

Here is the absorption spectrum for pure water. The higher the curve the higher the absorption. Unfortunately the majority of the useful thermal energy from the sun lies in the strong absorption bands. This is the opposite from solar cells which depend on the visible spectrum because of the bandgap energy of the photons needed to generate electricity.

http://vts.bc.ca/pics/waterspec.gif

Doc Nickel
05-16-2006, 03:48 AM
Besides that, the "water laying in a trough" shape is backward to focus energy- the convexity would need to face the sun, with the flat facing the "target". Light passing through the water trough would be distributed, not focused.

And, of course, the fact the sun would rarely be straight overhead, and liquid lenses would be difficult to "aim" in order to maximize efficiency.

Doc.

SJorgensen
05-16-2006, 04:11 AM
Ok, now that you've shot down the OBVIOUS problems with the idea, how about something positive on the up side?

My original idea was for a water filled plastic tube column that was stretched in a frame. It would be nearly symmetrical and stood up to face the sun.

I decided that it would be better to have a long tubular lens than have to maneuver something to mechanically orient it to the sun.

It wouldn't be much different of an idea to have a long flat sheet of glass with a contained body of water above it. The prime factors being the focusing of the light and the most inexpensive means of doing it.

I wonder about the problems of wavelength absorbtion. The idea here is volume and I think it would be substancially effective even with regard to some infrared absorbtion.

Thanks for the input.

Spence

Millman
05-16-2006, 04:21 AM
Spence, don't let these "experts" sway your ideas. You know, it's a good thing Edison didn't believe people like that either. Keep up the good work, this is why I started the other thread.

Rustybolt
05-16-2006, 10:24 AM
I always thought that a parabolic mirror, focused at a tube filled with sodium or some other agent that would hold the heat well. The tube would make a loop around a heat exchanger (radiator?)which would frovide steam which in turn would run a motor attached to a generator. Old large satillite dishes might be used.

A.K. Boomer
05-16-2006, 10:43 AM
I always thought that a parabolic mirror, focused at a tube filled with sodium or some other agent that would hold the heat well. The tube would make a loop around a heat exchanger (radiator?)which would frovide steam which in turn would run a motor attached to a generator. Old large satillite dishes might be used.


Yes this is a proven method, and if you want to have a zero maintenence version you dont use steam you use a sterling engine, they are out in space right now humping away 24-7 (no clouds out there!)

Evan
05-16-2006, 10:50 AM
Mirrors work just fine for two reasons. They can be up to 98% efficient at nearly all wavelengths and they also don't exhibit chromatic abberation as lenses do. You can't focus all the required wavelengths to a single focal point with a simple lens because the refractive index of any material is frequency dependent. This means that if the visible light is focused the infrared isn't and vice-versa. You may notice that some manual focus camera lenses have a red dot beside the the infinity focus position. That is the infinity focus position for infrared.

That really doesn't matter with a water lens as the infrared won't pass through anyway.

jburstein
05-16-2006, 10:51 AM
another problem with that is that your water won't be at the focal point of your parabola (assuming your plastic does form a parabola, haven't checked that, but I'm not sure I believe it). Not to mention reflection from the surface of the water, and aiming etc.

I believe the sane way to do it is a bunch of mirrors aimed at a collection point, which is backed up by some blackbody like material. Kinda like what you see in the movie GATCA. Which, I believe is a real solar farm somewhere out in the Mojave.

-Justin

Evan
05-16-2006, 11:03 AM
It won't form a parabola but instead a catenary which is similar but not the right shape.

[edit for sp]

jkilroy
05-16-2006, 01:33 PM
I don't know about going directly to steam in one stage, but you can get water damn hot with regular solar collectors. Maybe a two stage approach where you pre-heat the water though an array of conventional collectors, run it into an insulated holding tank, an old hot water heater. Then pump it into a "boiler" tube array (metal), through a check valve, and use a focused mirror array to heat it to steam. There is no doubt, that with enough focused sunlight, that you could make steam. Wasn't there a solar farm in California that used molten salts of some sort that recently shut down?

My question is how are you going to harness the steam? Traditional piston engine?

J Tiers
05-16-2006, 01:50 PM
Sorry to burst your bubble but it isn't feasible for one simple reason. Water is nearly opaque at deep red frequencies and near infrared as well as ultraviolet and above. That is why water looks blue. It transmits almost no heat.


To millman's comment:

The above is true, but may be irrelevant. Turn it around, and make the "downfall" a feature!

The water lense idea is feasible, IF the lense is assumed to be used as a 'feedwater heater", then anything it absorbs is pure gain.... it deposits heat in the water deirctly.

The water might be used to focus the remaining light energy on a pipe with a black coating to finish the absorbing of energy.

Now, I won't say there is no better way than this, I am sure there is. But this does neatly answer the "nope, aint a gonna work" response.

BTW, I believe any glass front mirror, or glass protected assembly will also waste some infrared, you need to use something transparent to infrared, or use a front surface mirror and no guard/cover.

Evan
05-16-2006, 02:08 PM
What won't work is trying to generate steam this way. You can certainly capture the solar energy as low grade heat and it would work as a pool heater. To make steam requires a very efficient concentrator. You don't just need to boil the water, you need to superheat it. This requires temperatures of at least 1000 degrees F. It just won't happen with a water "lens", too many physical principles are against it. It absorbs the heat as low grade thermal energy, it doesn't focus properly and the shape will be wrong even if abberation wasn't a problem to name just a few.

There is a reason you have never seen such a solar collector making steam and I am afraid it isn't because it's a new idea. There are a number of patents relating to this idea and they have not been successfully exploited.

Evan
05-16-2006, 02:13 PM
BTW, I believe any glass front mirror, or glass protected assembly will also waste some infrared, you need to use something transparent to infrared, or use a front surface mirror and no guard/cover.

An absolutely trivial way to make a nearly perfect, cheap first surface concentrating mirror of high efficiency is to stretch aluminized mylar over a circular sealed frame. When a small vacuum is pulled in the frame the mylar assumes the perfect shape and as a bonus the focal length is adjustable. Reflectivity of good quality aluminized mylar is around 88% including the infrared spectrum and replacement is cheap and easy. I have thought of using my old 8' satellite dish this way to make a small solar boiler and all I need is a large bag of round tuits.

RPease
05-16-2006, 02:23 PM
Oh..............and lets not forget the fact that water weighs over 60 lbs per cubic foot. If it "did" work, might take a lot to do any productive good........

Will your "plastic" hold the weight (of say 100 gallons) and withstand the 212+ temp at the same time???

Me thinks that we need some new materials that might not yet be invented..........but then again.......maybe they are......???

Evan
05-16-2006, 02:30 PM
Incidentally, when you drape a material between two parallels (water filled or not) it forms a catenary curve. This is the same curve assumed by a slack line hung from two opposite points, like a power line.

When you do the same thing with a flexible plane surface over a circle, such as the mylar I mentioned, then it forms a parabola, the correct shape for focusing light.

Rustybolt
05-16-2006, 02:53 PM
An absolutely trivial way to make a nearly perfect, cheap first surface concentrating mirror of high efficiency is to stretch aluminized mylar over a circular sealed frame. When a small vacuum is pulled in the frame the mylar assumes the perfect shape and as a bonus the focal length is adjustable. Reflectivity of good quality aluminized mylar is around 88% including the infrared spectrum and replacement is cheap and easy. I have thought of using my old 8' satellite dish this way to make a small solar boiler and all I need is a large bag of round tuits.

Couldn't you just line the dish with conventional mirrors? Keeping a vacuum going 12/7/365 might be a problem.

Rex
05-16-2006, 03:32 PM
find one of those big TV satellite receiver dishes, C-band. The solid ones work best. Try to get the tracking mechanism and everything that goes with it.
Mirror film mylar on the surface, stick it down with thick grease (really).
Mount a pressure vessel at the focal point, where there is already a structure for the original purpose. Fill with water, add inlet/outlet with one-way valves as appropriate. Supposedly these will boil water in under a minute, and keep it boiling as fresh cool water is fed to it.
Make a sun-tracking mechanism. Extra points for making it solar-powered. Double extra points for making it steam-powered!

ulav8r
05-16-2006, 03:39 PM
In 1974-75 there was an article in the Denver Post about a solar collector that an individual had in his back yard( I think it was on South Wadsworth Ave.). According to the reporter, a snow ball tossed into the focal point of the collector flashed into steam instantly. I had seen the collector many times. It was a parabolic (roughly, from observation as I drove by) dish covered with small mirrors, about 10 feet in diameter. Don't remember how the heat was used.

J Tiers
05-16-2006, 06:07 PM
If it is a "feedwater heater" it IS low grade heat........... and that is what you want.

One bit of heat directly input, the other in the blackened pipe. The effluent then goes to the high temp heater, which can be significantly smaller if the feedwater is already warmed up.

"Warmed up" might be pretty hot, on a comparative basis. Depending on flow rate, if you keep dumping a certain joules/sec into the same fixed volume of material , it will warm up. It can get pretty darn hot.

Someone may be forgetting that a given area has a given amount of energy input. No amount of finagling will get more energy per second into a given area. I don't care if you have perfect reflection.

If you generate steam, it is a certain small amount per second. If you heat feedwater, it is a certain larger amount per second.

Now, your feedwater heater means you can then have a smaller main boiler, since the energy addition in the boiler is smaller than if the water comes in 'cold".

You are adding heat to raise the temp to boiling, then adding heat to create the phase change to steam, and finally maybe super-heating the steam.

A feedwater heater takes care of the first part....... So, no it isn't "useless"........... sorry....

As far as pressure, in case you have forgotten, feedwater is not at boiler pressure until it is injected. and it isn't at max temp until the second pass through the blackened pipe. So, no, the plastic need not be pressure proof, nor necessarily capable of carrying 212 deg water.

I am not suggesting it is the best way, nor even a good way. I am merely pointing out some ways to think outside the box on this.

Nay-sayers may recall that bumble-bees cannot fly. That was apparently proven by experts, so if you see one flying, it is a delusion.

IOWOLF
05-16-2006, 06:26 PM
In 1974-75 there was an article in the Denver Post about a solar collector that an individual had in his back yard( I think it was on South Wadsworth Ave.). According to the reporter, a snow ball tossed into the focal point of the collector flashed into steam instantly. I had seen the collector many times. It was a parabolic (roughly, from observation as I drove by) dish covered with small mirrors, about 10 feet in diameter. Don't remember how the heat was used.

:eek: A death ray? Wow,imagine the ants you could fry with that.

Hell, Bar B que the neighbors dog:rolleyes:

Evan
05-16-2006, 06:31 PM
Couldn't you just line the dish with conventional mirrors? Keeping a vacuum going 12/7/365 might be a problem.

The problem with a satellite dish is the extremely short focal length. This requires the boiler to be placed directly in front of the dish which blocks a lot of sun although some of that will help heat it anyway. Also, the dish isn't very accurate at optical wavelengths. A simple fish tank air pump can be used as a vacuum pump and could be powered by a solar panel feeding a small inverter available for a few dollars. Those pumps only require a few watts and can pull about 15 water inches vacuum. The same solar power can be used to run the tracking mechanism. It won't need to run 12 hours per day either, at most maybe six on a good day.

With a longer focal length it becomes practical to place the receiver on the ground at an offset focal point and move the dish accordingly to maintain focus on that point. That is exactly how the heliostats at the Barstow Solar One plant in Ca worked.

The concentration factor is all important. A ten times concentration factor only improves heat efficiency by a factor of 4. The higher the concentration the better. Concentration ratios of about 100 to 1 or better are required for solar steam generation.

A simple computer control can be used with low power servo motors to track the sun or an even simpler feedback system can be used to keep the beam on the target.

Evan
05-16-2006, 06:33 PM
Nay-sayers may recall that bumble-bees cannot fly.

Damn, I wish people would stop repeating that. Nobody ever "proved" that bumble bees can't fly. The original math showed conclusively that considered as a fixed wing object they cannot fly. In other words, they can't glide. And, sure enough, they cannot.

IOWOLF
05-16-2006, 06:46 PM
Yup, and the sun revolves around the Earth.

darryl
05-16-2006, 09:41 PM
Some years ago I saw a solar collector which was a long structure in the east-west direction, and had a stainless steel sheet formed into a parabolic shape as the reflector. This was not a dish shape, but rectangular. Any flat sheet can be bent this way. Imagine cutting a tube in half lengthwise, and one half of this is the reflector, though the tube shape is not parabolic. If it were then this is the shape you'd have. The solar collector was fixed east-west, but could be 'pointed' from the horizon to vertical, and a tracking device merely kept it pointed to the particular elevation that the sun was in the sky at the moment. The collector itself was a tube suspended in front of this reflector, and it didn't matter if the sun's rays came in from the side or not, they would still reflect and become focused on the back side of the tube somewhere. With the sun in the 12 oclock position, the entire tube got reflected energy, and at any other time, some of either end of the tube would be in the dark, while some energy would be spilled out of the structure at the other end. Because the structure was longish, this didn't represent much of a loss, as most of the collector tube still got 'lit up'.
As I recall, the tube could have been made as one long passage, or as several separate passages. With the separate passages, they would be plumbed in parallel, with the feed and drain tubes becoming part of the structure that holds the tubes in place at the focal line. With the parallel approach the water pumped through would be heated more consistently, and thus more energy would get absorbed by it. You didn't have cold water entering at one end, and super heated water exiting at the other, you had cold entering each section, and hot (but not super hot) exiting each section. A collector pipe gathered the hot water from each section, and a feed pipe fed the cold to each section. I hope I'm describing this in a way that makes sense.

As far as steam, I don't know if the parallel approach would allow the water to heat that much before it exits each section. I can see a more modern approach that would have the cold water entering the collector pipe from fixed spots spaced out along it, (on the side facing the sun) with each spot controlled by a simple valve responding to heat from the other edge of the pipe (that facing the reflector) Where the tube was getting hot from reflected energy, the valves there would automatically open the cold water feeds opposite. Maybe a light spray from these feed points would absorb enough energy to flash into steam, which would exit automatically from both ends of the collector pipe, being under some pressure at this point. I'm sure this would be entailing a lower total feed rate of water through the system, but with a higher temperature output. Hopefully, this would be steam at several hundred degrees, as it would need to be if under some pressure.

At any rate, the only tracking mechanism was to pivot the reflective 'trough' up or down to match the elevation of the sun in the sky. Nothing follows the sun across the sky, making the mechanics of this a lot easier.

The basic idea here is the long collector array, well grounded, vs the large parabolic dish, with it's attendant two axis pivoting structure requiring a much more significant mounting, and control. The dish has the better potential to produce steam, since there would be a higher concentration of reflected energy impinging on a smaller collector point, but everythihg here moves so there's more of a plumbing problem than with the linear parabolic trough type collector.

Anyway, just recalling a few idea from the past that seemed to make some sense to me.

rollin45
05-16-2006, 10:07 PM
I believe there is a power company in Australia which is using solar heated water as a pre-heat for a coal fired powerhouse. The idea being that it ups the efficiency. I am not sure if this is online as yet or not.

I have an idea which I am scrounging parts for, that being, to use a large parabolic dish which will track in two dimensions, to heat oil. It will of course have to be leak proof, but the idea is that one can heat the oil to a much higher temperature without worrying about pressures. The heated oil will be stored in a large dewar. Then a heat exchanger with an oil side and a glycol side will heat my shop via underground plastic pipe circuits.

I've got a couple of large pressure vessels, a suitable heat exchanger, the parabolic dish and quite a lot of the other miscellaneous bits and pieces. I lack the time right now, but retirement is a couple of years away and then I'm going to give it a whirl.

rollin'

J Tiers
05-16-2006, 11:18 PM
Damn, I wish people would stop repeating that. Nobody ever "proved" that bumble bees can't fly. The original math showed conclusively that considered as a fixed wing object they cannot fly. In other words, they can't glide. And, sure enough, they cannot.

But that is SOOOOOOOOO an example of "in the box" thinking........*

And the statement is SO LOVELY as a retort, you can't possibly wish that people would stop saying it, not REALLY......... :D

*because nobody but a da#n fool would ever consider a bumblebee as a fixed wing flying machine..... not if they ever saw one.......

Mad Scientist
05-16-2006, 11:22 PM
SJorgensen:

You should check out the “Phoenix Turbine Builders Club. “ You find a bunch of information on building solar collectors by people who have ACTUALLY BUILT THEM. The following links are to a guy has an array 37 square foot of mirrors that was making 1060F in December!

http://phoenixnavigation.com/ptbc/articles/ptbc43.htm

http://phoenixnavigation.com/ptbc/articles/ptbc48.htm

P.S. Once you get you solar panel up and running I can loan you a Tesla Turbine to play with. :D

JCHannum
05-16-2006, 11:28 PM
Damn, I wish people would stop repeating that. Nobody ever "proved" that bumble bees can't fly. The original math showed conclusively that considered as a fixed wing object they cannot fly. In other words, they can't glide. And, sure enough, they cannot.

Actually, researchers at Berkeley seem to think that the original premise is correct;
http://www.pass.maths.org.uk/issue17/news/bumble/index-gifd.html

ASparky
05-16-2006, 11:43 PM
Ok this is the std science view, not that that means there is not a loop hole somewhere, but I present it as a starting point.

Black pipe or similar under glass is V good at taking in the heat, when the pipe (water or fluid inside) is coolish. So far so good.

Sunlight from the sun unconcentrated will heat black pipe under glass to about 80C. If you insulate it and do fussy stuff you can get to 160C. At that point the heat loss will match the heat gain. I.e cooling down as fast as its heated up by the sun.

This is borderline for running a steam engine, or even a sterling efficiently. Need V large pistons/cylynders to do well. Steam engines are really inefficient. No hope of running a turbine efficiently. As a converter of low grade heat, steam engines are not great. Lotsa room for inventors here. If you assume collection area is no problem, the issue shifts to how to move all that water around without losing the heat.

Want hotter ? Concentrate the sunlight. Utlimate limit is the temperature of the source, sun is pretty hot so even after the atmosphere etc there is plenty of room to go.

Mirrors are easy and cheap. Aluminium works. No need to be fussy about chromo aberation, fuzzy focus, super clean mirror, heat distortion etc etc. If most of the energy gets to where you wan't all is ok - you arent taking a high res, hig quality picture of the sun.

Now the hard part starts. You do want this acre of mirrors to stay on track when the wind blows - big sail. Ok make mirrors more rigid. Now survive a catgeory 3 storm? Ok much more solid and heavy or someway of hiding, moving to a protective locker required.

Concetrator probably means you need to track the sun, computers can do that - even work out the angle for each mirror. But moving this acre of heavy rigid mirrors requires a lot of expense of motors or whatever and a lot of energy.

Ok now you have the plan for energy domination, work the costs out, work out the energy yield and subtract the energy to run the motors etc. Now work out what the energy you have left can be sold for and how long the mirrors system will last. Ie. what it is worth. If you are lucky you will find that the return on investment works out to be 5% per anum on the investment. In most cases it is an outright loss.

Any strict investor is going to stick their money in the bank and earn more.

If a big enough system in a very sunny enough place and a big enough market nearby, and oil stays at around current levels, it starts to pay - but only just.

Evan
05-17-2006, 12:04 AM
Actually, researchers at Berkeley seem to think that the original premise is correct;


No, they don't. They just can't figure out why it is so efficient when flapping its wings.


*because nobody but a da#n fool would ever consider a bumblebee as a fixed wing flying machine..... not if they ever saw one.......

Yes they would if somebody asked them what the wing loading of a bumblebee is, which is what happened. Then you must consider it as a fixed wing object, just like the natural biplane, the dragonfly. Which btw has a much lower wing loading and glides just fine. Bumblebees are worse than the space shuttle which has the glide ratio of a streamlined manhole cover.



Want hotter ? Concentrate the sunlight. Utlimate limit is the temperature of the source, sun is pretty hot so even after the atmosphere etc there is plenty of room to go.


Yep, that is the secret. If you want steam you must have temperature, not just heat. As I said, at least 100 times concentration is required. I experimented with a linear parabolic collector prototype and it gave about 35 times concentration. Not enough to produce boiler steam but it will cook a hot dog.

http://vts.bc.ca/pics/cooker1.jpg

Scatterplot
05-17-2006, 12:25 AM
You know, I kinda don't want to do the math, but are we sure that it would form a caternary? I know under a distributed load (a cable's weight) it would be a caternary, but there will be more weight in the middle of the plastic since it has more water above it. I would seem to think that it would be a distributed non-constant loading, which would be hard to do the math for. It would be more like the parabolic shape of a mylar disc over vaccuum method, but I don't know.

Ryobiguy
05-17-2006, 12:28 AM
Thanks to this thread I now know what a Tesla turbine is. Sounds like a fascinating device, I've been trying to figure out how the thing works, specifically plate spacing and mostly how many of those smooth plates are needed. Then I wondered if hard drive platters (spaced closer together) could make a quick and dirty DIY turbine, since they are very smooth.

Also, is the parabola only formed via the vacuum & mylar method when using a circular form? If you had a really long rectangular form, covered the top with mylar, then vacuumed it below, would the center part (away from the cupping of the ends) be parabolic?

I also just saw some pictures of a guy mounting a drill press on a horizontal 4x4 above a pile of dirt, and using it to spin a parabolic shaped form down on the mound to smooth it into a parabolic shape. Then he covered it in concrete and made it into a mold for making fiberglass parabolas.

gmatov
05-17-2006, 12:51 AM
This might be old hat, hell, I am old hat, but 30 -40 years ago, the parabolic trough reflector was the greatest thing. The length was not critical, but the longer it was the hotter the exit temp was. Vaccuum forming was not involved, simply a trough of the right shape, and a reflective surface that would be able to conform to it. A thin mylar sheet, for example. Don't rcall if they had that, then.

As to guiding it, no motors involved, as far as electricals went. Were pneumatic sylinders, captive gases. As the Earth revolved, one cylinder was shaded by the trough, the other was exposed, the gases contracted and expanded, the trough rotated to the hottest focus.

Then too, there are eutectic salts, can you concentrate enough heat, you can store enough heat for your own use, if not enough to sell.

The size of the parabolic reflector would have to do with the concentration of heat. I haven't been into solar for a while, but I think it is something like 50 watts per sq. ft, on an average day, some 170 BTUs. Not a lot, but anything can help your own circumstance.

Cheers,

George

BTW, If bumblebees can't fly, why can't I hit the sumbitches with my can of Raid that will shoot 20 feet? They're diggin' holes in my porch beams, and I am a bit PO'd. These ain't really bumblebees, these are the big assed Yellow Jackets, size of your thumb.

Evan
05-17-2006, 01:01 AM
The circular form is an essential part of the math of forming a parabola. A parabola is a conic section as is a hyperbola, ellipse and a circle. All four curves are cases of an ellipse, the circle is an ellipse in the limit case of equal major and minor axes, the ellipse itself is where the major and minor axes are unequal but not infinite. The parabola is an ellipse with the major axis infinite and the minor axis asymptotic and the hyperbola is an ellipse with both axes infinite in the limit.

The catenary may be unloaded or loaded. The equation is the same. The catenary shape is formed by the weight of the material making the shape. Adding weight in the form of a supported liquid results in exactly the same distribution of weight as when unloaded since the depth of the liquid in the Y direction is controlled by the shape of the catenary to begin with. Therefore the loading only varies by degree, not by distribution.

If the catenary is not completely filled then it becomes a center loaded catenary with a slightly different solution, but still a catenary.

Rich Carlstedt
05-17-2006, 01:06 AM
George
The reason you can't hit the wasps is because you are chasing them.
Let them come to you. Take a 2 Litre clear plastic bottle, like coke or pepsi.
Empty the bottle, and cut the top half off with a sharp knife, right where the straight sides starts at the top. Now invert the top (No Cap?) and push it down into the staright section about 1 inch.
You want the top end which is now upside down to stop about 2 inches from the bottom. Put a cup of sweet (not diet !) smelling pop, like Orange, and maybe a piece of old meat from teh grill. Set it out and it will gather them
up for you..and they will drown in the trap.

Sparky said he could get 160 C with his unit..thats about 80PSI of Steam as i recall..Are you sure sparky..Thats what Jorgy wanted.

My nephew in Michigan could not get over 195 F when he put tubes in a hot box.
If the water is exposed, it condenses on the glass and screws up your prisms !
There is a flash stem collector running in Arizona.. try looking for it.
Rich

J Tiers
05-17-2006, 01:09 AM
Yes they would if somebody asked them what the wing loading of a bumblebee is, which is what happened. Then you must consider it as a fixed wing object, just like the natural biplane, the dragonfly. Which btw has a much lower wing loading and glides just fine. Bumblebees are worse than the space shuttle which has the glide ratio of a streamlined manhole cover.


Sure, the wing loading of a bumble bee is meaningless unless its flapping them, because that is how it flies...... .

It has all the real meaning of room temperature dry water....... just silly

And dragonflies "flap" their wings of course, they are much more a natural helicopter than a biplane..... look at a slow motion movie of a hovering dragonfly, balance of opposing forces......

Solar power is obviously "practical", nearly all power on earth is solar in origin, even oil. The issue is that it needs to be collected and used efficiently.

Biological stuff is efficient, mechanical is not.

Look how much work you can do based on the caloric value of food, and you find people are pretty efficient. If you burned the equivalent food and boiled water to make power etc, you'd never get anywhere on what a person eats and then slings coal all day on.

Evan
05-17-2006, 01:21 AM
The point of the original bumblebee question was simply to determine the wing loading. You can't do that if the flapping is considered because that is a dynamic situation. This wasn't even an "official" study but somehow it "escaped" into the wild of the press. Now, a natural reaction of many if not most people is to ridicule something that you don't understand, especially if it makes you feel inferior because you don't understand it. Science and math are very common targets for this treatment hence the "bumblebees can't fly" story.

For some reason it makes people feel better if they can make it seem the the information they don't understand is foolish, and then by association the person who presented it, is a fool. Stories like this have a life of their own because the idea is so attractive to so many, especially reporters who seem to be abnormally ungifted in the field of science.

Guido
05-17-2006, 01:23 AM
Maybe less than 50 miles in distance, but, at Yermo, one can see the computer manipulated mirrors playing the sun onto a black colored, tank like, elevated target. Capable of making steam and electricity, profitably, probably 350 days per year. Nearby is an experimental coal to gas converter using coal from Colorado. Makes electric power, experimental for now, but profitable when located closer to coal supplies.

Few miles west, Kraemer Junction. Long, computerized movement, parabolic mirrors playing the sun onto long pipes containing flammable liquid of some kind. Ultimately generating steam for turbines/generators for the grid. Profitable at crude oil prices of $40 and up.

Just west of Kraemer, Rocket Site Mountain. Most NASA rocket engines tested here, cantilevered over the steep sides. Part of Edwards AFB where stuff has been happening since Yeager, Rutan, Edwards did their thing. 'Twas here we saw Shuttles return from space and Voyager return from round the world/one tank fuel flight. Ever see 5 superbowls wrapped up in one presentation.

On west to Boron, I believe the largest open pit mine in world? Produces about 95% of world's borax supply?

Ten miles further west to Mojave Airport where Bert Rutan does his Spaceship One thang. First privately licensed American spaceport.

For the next 25 miles or so, windpower systems of all kinds atop the Tehachapis. Been on line since late '70's. Government support long since whittled away, idea works, everyone is happy.

All the above open to public view, courtesy of your government and private enterprise. The best job I ever had was being able to call on these industries at any time of the year. They all needed ground water supplies.

G

J Tiers
05-17-2006, 01:34 AM
If you don't like "bumblebees can't fly, then I offer you the "everything has been invented already, we can close the patent office" statement.

IIRC, statement made ca 1900 or so.

There's lots more, all narrow thinking inside a tiny box.

Why was the 'wing loading" so important anyway?

And it was my impression that statement was very old anyway, 1920s or so....

In any case, solar power is clearly and obviously viable. Every available renewable source is solar in origin anyway.

Ethanol fuel is obviously solar, directly, even if horribly inefficient when corn is used instead of cellulose or sugarcane, starch or sugar-bearing root crops, etc.

Tidal power is the least solar, but it isn't renewable, it is really the stored energy of the moon in its orbit. Geothermal is non-solar, non-renewable.

The very long term view makes it abindantly clear that no more energy can be used than comes in as sunlight unless you wish to input extra to the system, waste reactor heat, CO2, etc, etc.

Even the direct use of solar power will have cosequences to weather.

Evan
05-17-2006, 01:59 AM
Why was the 'wing loading" so important anyway?


I guess because somebody asked the question.

SJorgensen
05-17-2006, 02:23 AM
I'm fine with knowing that this won't create a perfect lens. I'd did a small experiment and it seemed to show that the light will be concentrated instead of dispersed. I only had a couple of minutes before work, and all the water spilled out and then I had to get to work. One question that I hope someone can answer tomorrow if I don't answer this experimentally myself is; will a water solar lens increase the output of a photovoltaic panel?

ASparky
05-17-2006, 02:57 AM
The 160 degrees may be off a bit. It depends on how close to the equator you are. You can look up blackbody radiation for the watts per square meter radiated at x temperature (in Kelvin) and the watts per square meter for sunlight at your lattitude transmission curve of glass (if glass covered) and sharpen up your computer to work out a number. In practice you will then need to derate it a lot for heat loss by conduction/and convection unless your tube is in a vacuum.

The bumble bee thingy has two issues one is that they won't glide. Same as a helicopter wont (yeah it can autogyro). The next issue was that the wing flapping seemed to not produce enough lift either or more accurately it should have been flapping faster. Modern physics has shown that this is cause the BB cleverly creates vortexes at part of the stroke that it then gets extra lift off of by flying through the same vortex later in the stroke.

see http://www.apologeticspress.org/articles/2528 for more.

Evan
05-17-2006, 03:28 AM
will a water solar lens increase the output of a photovoltaic panel?

The answer is maybe. Here is a better absorption spectrum for water:

http://vts.bc.ca/pics/wspectrum1.gif

It depends on the type of solar cell used. Amorphous cells are cheap but inefficient and they utilize the red end of the spectrum. If you look at the curve above you can see that the absorption in red is about 20 to 40 times greater than blue so you would have to concentrate to just break even. Polycrystalline and monocrystalline silicon cells are much more sensitive to blue and water is very transparent in blue so such a concentrator might be a benefit. It may also help by filtering the heat out which is a major cause of inefficiency with photovoltaics.

However, cells intended for 1 sun irradiance should not be used in a concentrator. Because of internal resistance heat will be generated regardless of how much heat reaches the cell by radiation. Concentrator cells are normally designed to be used on a heat sink.

We have a lot of people around here that are off the grid including quite a few of my customers. I sell high quality synthesized sine wave inverters made by MGI for applications where inverter power quality is critical. Because of the climate and lack of sunlight for much of the year off grid solutions must be a combination of solar, wind and generators. Water power isn't practical on a really small scale because it is frozen here for nearly half the year.

Mad Scientist
05-17-2006, 09:54 AM
[QUOTE=Ryobiguy]Thanks to this thread I now know what a Tesla turbine is. Sounds like a fascinating device, I've been trying to figure out how the thing works, specifically plate spacing and mostly how many of those smooth plates are needed. Then I wondered if hard drive platters (spaced closer together) could make a quick and dirty DIY turbine, since they are very smooth.

Yes the Tesla turbine is a fascinating device, and yes hard drive platters and the smaller CD’s have been used to make turbines. A .045” to .050” spacing between the discs is optimum when using compressed air to run it. Also keep the number of rotor discs low, (5 to 7) or it will take to much air to run it.

At quick glance the turbine is a remarkable engine due to its inherent simplicity, that is until you try to build one, and many have built working engines. (That easy.) However the trick is to not only make a turbine that runs, but one that runs efficiently!

ulav8r
05-17-2006, 11:01 AM
Does anyone make a photo voltaic cell that is water cooled? Would this improve the efficiency of the cell and provide heated water for direct usage or heat production?

Evan
05-17-2006, 12:09 PM
Yes they do. Capturing the waste heat helps the overall system efficiency a lot.

[added] The reason heat reduces the efficiency of photovoltaics so much is because it increases the internal resistance which is a self re-enforcing problem as when the resistance goes up then so does the heat generated by internal loss.

jontwo13
05-17-2006, 04:19 PM
I saw steam blowing out of a solar collector at the mother earth testing site in north carolina USA back in the early 80's. There is s or was a company in Texas that was using a salt pond to generate steam for manufacturing. A salt layer lets the solar heat in and traps it. It is nasty if you get a leak.
sol

Al Messer
05-17-2006, 04:24 PM
The students at Georgia Tech University did something similar to this about 35 years ago using a parabolic mirror to heat the coils of a monotube steam generator. You may want to check their archives.

Scishopguy
05-17-2006, 04:31 PM
Talking about a great concave mirror for cheap-cheap, The Mythbusters did a segment on the myth that the Greeks had a death ray formed by mirrors. They tried all kinds of mirrors from the polished bottom of a Coke can to ice cubes in the shape of a lens. The real gem that came out of all that was the mylar film stretched over the end of a large pipe and drawn into shape with a vacuum. That stuff worked liike gangbusters!!! It was the quickest to set fire to the test material. The rest of the solar steam generator is tried and true technology.

Most folks will tell you that whatever it is has no commercial value. Probably true but it is fun to screw around with and you can probably make it work good enough to power up your emergency backup batteries or run your greenhouse, or something.

Jim (KB4IVH)

Evan
05-17-2006, 04:54 PM
The real gem that came out of all that was the mylar film stretched over the end of a large pipe and drawn into shape with a vacuum.

Yep. I know the guy who did that. He works in the space program. I gave him the idea of using a mylar mirror for the Mythbusters challenge.

His name is Mike Bushroe. He sent me this pic of him with the rest of the contestants and Adam and Jamie. Mike is the guy in the middle with the saturn tee shirt and the hat.

http://vts.bc.ca/pics/mbdeathray.jpg

dicks42000
05-17-2006, 09:29 PM
Evan makes a good point, as usual;
Why are there so many people who are paid to offer opinions/ thoughts on matters of science & technology that don't practice in the field or have a science or engineering degree/ diploma/ background ??? (Forrest Addy excepted.) Sure a few sci-fi writers were tech people....Asimov, Clarke, Shute, etc...
How many machinists are popular writers or reporters. (Leave the Bedside Reader, etc out of it.) I mean mainstream press.
Maybe technologists aren't good communicators, or maybe Joe public just gets bored with us...
Sad....

SJorgensen
05-18-2006, 12:31 AM
I think it would be fun to have a contest. I'd like it to have certain simple benchmarks. I think it should have two active priorities in mind.

First would be cheapness. Cheapness is good. Every dollar must be accounted for, or at least a reasonable estimate of costs must be included. Points should be subtracted for complexity, and added for simplicity. I don't think any points should be added for a small surface area like a dish. The main reason being that there is a limit what you can do with a dish or a mirror especially if each requires complex three axis controls. There are large surfaces like rooftops available, so area shouldn't necessarily be a hindrance. Small and efficient is very good; in fact it is toward the perfect. It is perfect in a way that reminds me of that quote "The perfect is the enemy of the good." However, in this case total output is better served by quantity instead of quality. It reminds me of that quote often attributed to Stalin that was quite clever. "Quantity has a quality all its own."

On Evan's chart of the spectrum absorption of water I have trouble interpreting the information. I can't relate the 10,000CM^-1 to an actual measured depth of water. I need more education. I envision a water lenses that might be 6" or 8" thick in the middle and about 3' wide and 100' long. I don't think enough spectrums would be absorbed to appear with a blue or any other color that would be perceptible with the human eye. If the average focal point is say 36" below the water lens and let’s say it is about 12" wide, then perhaps another simple water lens could further concentrate the energy. Any pipe running 100' through a gauntlet like that is going to get pretty hot. Water judiciously, or in a metered way, introduced into this pipe should generate some steam and if it can be maintained above 366 degrees farenheit it could continuously generate 150 psi. The question is how much water would it take to keep the solar energy of 3,600 square feet, concentrated into a space of 100 square feet by the first lens and then into 33.3 square feet by the second, from rising above 366 degrees.

A frame of 36" x 100' with a top sheet and a bottom sheet of Mylar or other clear sheet material would not be very expensive to construct. I'll build a test much smaller model of course just for fun.

Second factor in the contest would be the work accomplished. I'm going to start out like I did as a kid. I'm probably going to fry a spider, and then light a leaf on fire. Next I'll probably try to generate some steam. First I'll run a whistle, and then I'll try to turn a piston motor.

Evan
05-18-2006, 01:09 AM
Spence,

The human eye is almost infinitely adaptable to changes in color balance. You will not be able to detect the blue shift caused by passing sunlight through water but the solar cells or other collector will.

Here is the basic problem with generating steam. Heat is additive, meaning that if you collect a little heat and then a little more and so on then you end up with a lot of heat. Heat is NOT temperature and temperature is NOT additive. Collecting a little low temperature heat over a long collector gives you a lot of low temperature heat, not high temperature.

The only way to produce high temperature is to concentrate the radiation by a very significant degree. If it is 3' wide then it will have to focus the entire spectrum to a line less than 1/3 inch wide. You can't do that, the laws of optics don't allow it for several reasons. The sun isn't a point source, it has an apparent diameter of 1/2 degree. The colors don't all refract to the same place in a simple lens no matter what the material, shape or the quality. You cannot make a single element lens that will produce a concentration factor of 100 or more.

The temperature rise available from a collector depends on several parameters one of which is the apparent temperature of the source. The sun is certainly hot enough so that isn't a problem. But, when you collect heat on a black body it also radiates it away. The relationship between collector efficiency in absorbing heat is precisely related to the efficiency in radiating it. It's called the Stefan-Boltzmann law. The emissivity is equal to the absorption.

The emissivity is directly proportional to the fourth power of the black body's thermodynamic temperature which is why the concentration factor must be so high to produce steam. The collected heat radiates away faster as the temperature increases so you must have a very high temperature to impart sufficient temperature to the working fluid if it is water. There are other working fluids that will work with much lower temperatures such as ether and propane or even gasses such as helium but that tends to complicate matters a lot.

Ryobiguy
05-18-2006, 01:48 AM
Maybe this is a dumb idea for reasons someone might so kindly point out:
If you try to boil water in an slight vacuum, doesn't it boil at a lower temperature? Maybe this doesn't yield any useful work, but is there any way to use this to lower the temperature requirements? It probably would just pressurize as it boils, and then you'd be left with the usual boiling point.
The idea is to have a closed system (I guess with some air space in it) and pump out as much air as possible to lower the boiling point of the water.

Since water doesn't seem to absorb heat directly, are there any dyes or something that can be added into the water to absorb the heat in a clear collector tube? I bet everything's probably transparent in the critical frequency bands...
But, it seems like if that would work it would help reduce heat radiation, since much of the heat would go further towards the center of the collector tube (deeper than using a black coating on the outside of the tube.)

Something related that comes to mind is a news article I read a few weeks back was about water traveling uphill on a hot piece of brass which had a fine sawtooth pattern (something like .001" per step.)
It was something about a very fine layer of steam floating up in concentrated spots (one part of the sawtooth profile,) which pushed the water uphill. It said it was similar to how a large drop of water will float rather frictionlessly on a very hot frying pan. Unfortunately I couldn't find any further details on it.

Evan
05-18-2006, 02:09 AM
It probably would just pressurize as it boils, and then you'd be left with the usual boiling point.


You answered your own question. To get any real working efficiency from a working fluid it needs to be superheated to above the critical temperature and pressure of the fluid. Above that temperature it cannot exist as a liquid and any increase in temperature produces a corresponding increase in pressure.

Definition of critical temperature:
The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.

Definition of critical pressure: The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.

For water the critical temperature is 374C and the critical pressure is 217 atm.

For propane it is 97C and 42 atm which is a much easier range to work in.

SJorgensen
05-18-2006, 02:18 AM
Thank you Evan. I hope that you realize that much of what you said can't be understood by lamen like me. I accept the fact that you are probably correct in all your assertions.

First, I understand that the eye, although very sensitive in many ways to color shift may not be very sensitive to unseen frequencies like infrared that are very important, I'm not yet convinced that a water lens is in any substancial way, incapacitated by the heat absorbtion, or by the frequencies asbsorbed by the water in the lens. I would need to understand that graph that you provided and I need to give it some scale that I can understand. It isn't your fault, but I don't understand it yet.

I'm not sure that I understand what you meant about the issue of heat and temperature. As I understand heat, it is a measure of energy. Temperature is also a measure of energy. As I understand it, if energy is added into a system at a rate that is greater than energy escapes or radiates out, then the temperature will rise. If energy escapes or radiates out faster than it comes in, then the temperature will fall. I don't know anything about any demarkation in physics about low temperature, or high temperature heat. I'm sure there are other factors that I don't understand.

I could understand a status situation where the emissivity rate is equal to the absorbtion rate, but I think that that could only happen when there is an equalibrium state. This only means to me that an equalibrium will eventually be reached, but not to say that huge amounts of energy can't be harvested before that state is ever reached. I'll have to learn more. Thank you Evan for introducing me to or about the Stefan-Boltzmann law. I'd rather learn from you about some of these things than from most of the professors that I have ever had.

It isn't enough for me to know about a law. I have to incorporate it into everyting else that I believe or understand. This isn't easy.

Thanks again Evan,

Spence

Evan
05-18-2006, 02:33 AM
Temperature is a measure of the kinetic energy of a particle. Total heat is a measure of how many particles have that temperature. A candle flame has a much higher temperature than a bathtub of warm water but the bathtub of water contains far more heat. This can be easily seen if you visualize trying to heat the bathtub with a candle. Plenty of temperature but not enough heat.

In the case of solar power it is the opposite, plenty of heat but without concentration not enough temperature because the object being heated radiates away the heat.

In the case of hot water collector panels this is partly overcome by using glass covers over the collector. When short wavelength radiation (near infrared) heats the collector the wavelength of the radiation is changed to a much longer wavelength as low temperature heat.


The temperature of packet of energy called a photon is directly related to the wavelength (color) even if the "color" isn't a visible color (infrared).

The glass has good transmission at short wavelength but is nearly opaque at long wavelengths. This is the greenhouse effect. Water has poor transmission at all the wavelengths below the visible spectrum so a water concentrator will mainly absorb the heat in the water itself and then reradiate it. What gets through is mostly the visible spectrum with a bias toward the blue end. While this is a high temperature it isn't a great deal of heat because it is only a small part of the entire spectrum of energy emitted by the sun.

If you look at the graph the result of filtering the solar radiation through the water is that you only end up getting the part that corresponds to the dip in the curve in the visble spectrum. The rest is filtered out although you can't see it because it isn't visible.

An opposite example of this effect is a piece of exposed and developed color film like the leader section of 35mm film. It appears nearly black in the visible spectrum but in the near infrared it is 96% transparent. It makes an excellent infrared filter.

Scishopguy
05-18-2006, 12:40 PM
QUOTE:
Yep. I know the guy who did that. He works in the space program. I gave him the idea of using a mylar mirror for the Mythbusters challenge.

Evan,

It was such a shame that the large scale model was destroyed in shipment. I would have loved to have seen how that baby would have done against the wooden ship. I can smell that smoke already!

Jim (KB4IVH)

Evan
05-18-2006, 12:48 PM
I have never seen the episode. What device was destroyed? We are way behind on the schedule in Canada, maybe a year. I won't be seeing it either unfortunately as I have cancelled all but the most basic TV satellite service. I never watch TV anymore.

Mike sent me that pic when he was still under a NDA but I think it is safe to assume that since it has aired in the US that the NDA no longer applies. Mike was on the Huygens Lander imaging team and was responsible for assembling many of the composite images published from that mission.

I haven't been in contact with him recently but last I heard he was writing a short book on his "Mythbusters experience".

pcarpenter
05-18-2006, 01:09 PM
I always get a kick out of people's reaction to "naysayers". Rather than looking at what they say and evaluating it, folks often just attack the naysayer as being negative. Some of us, by personality, tend to look at things for the plusses and minuses in an idea. Pointing out the negatives is not negative. Millman made reference to Edison. One of the most important steps in finding a solution to a problem which will work is sorting through those that won't. I'll bet that Edison would have appreciated someone *with prior knowledge* had spoken up and told him in advance *why* a filament would not last without a vaccuum....for example. He spent a while looking for the right filament material as I recall, and the vaccuum ended up being just as important as the filament.

Always remember there is a difference between shooting down a particular solution because it will not work, and shooting down the overall end goal. Cheap energy is a great goal, but insisting on doing it through the superheating of water using a big parabola full of water may not be the way to get there. Sometimes you have to get beyond your initial assumptions about how to do something in order to get on to a way that actually does work. I know I can certainly point to many occasions on which my "plan B" ended up producing a working solution that I would never have gotten to if I had never given up on "plan A".

In short, there is no reason to ask others about the validity of your idea if you don't want them to tell you why it will or will not work The difference between just naysaying and good advice is that the latter is truly backed up with verifiable and useful information.
Paul

J Tiers
05-18-2006, 01:45 PM
I always get a kick out of people's reaction to "naysayers". Rather than looking at what they say and evaluating it, folks often just attack the naysayer as being negative. Some of us, by personality, tend to look at things for the plusses and minuses in an idea. Pointing out the negatives is not negative.

The difference between just naysaying and good advice is that the latter is truly backed up with verifiable and useful information.
Paul

A "naysayer", "expert" or not, may be correct. Or they MAY have a correct answer to the wrong question. Voluminous supporting data and "proof" may be irrelevant to the matter at hand.

At the risk of re-annoying Evan, the famous bumblebee example is an outstanding example of that.....

IF a bumblebee depended on gliding, OR a bird-like wing beating, it could not fly.....

If someone asked about "making" a bumblebee the way they are actually physically made, they would be told to go back to school, because it is intuitively obvious to the most casual observer that it won't work, couldn't fly as-drawn.

The key data that WE have is that we know they DO fly.

Starting from scratch, it's crazy..... unless you have the insight to see that you do NOT have to make the same assumptions that the nay-sayers make.

So, whenever you are given an answer, ESPECIALLY by an "expert", the very first thing to do is to check on their assumptions.

It is very possible, (even likely, in some cases) that their assumptions are flawed and that you and they are talking about different things without realizing it.

Your idea may be OK, or it may still be no good. But if it is no good, the reason may be something totally different than what you were told.

Evan
05-18-2006, 01:53 PM
There are many ideas that at first glance look good. One that comes to mind is the ornithopter. It's how birds fly and they do it very well so why shouldn't it work? It doesn't work because of the laws of physics and the mass cube/square principle. You can't make a practical flapping wing with available materials big enough to carry people because the mass of the wing structure increases as the cube when the size and lift is squared.

This sort of thing comes up all the time and the patent office records are filled with "inventions" that look good on paper but are fatally flawed because they ignore some or many physical realities.

Some of the laws of physics are intuitive and some are not. It only takes one such flaw to invalidate an idea no matter how good it seems at first glance.

Solar energy is emminently practical as a power source in many places but just as with any other source of energy it has contraints that must be accomodated for it to be useful.

J Tiers
05-18-2006, 05:52 PM
There are many ideas that at first glance look good. One that comes to mind is the ornithopter. It's how birds fly and they do it very well so why shouldn't it work? It doesn't work because of the laws of physics and the mass cube/square principle. You can't make a practical flapping wing with available materials big enough to carry people because the mass of the wing structure increases as the cube when the size and lift is squared.



The assumption being you want to carry people.... in which case it probably IS true.

BUT if you wanted to "build" a flying animal, the reasons it won't work for cargo carrying are irrelevant.

Of course from THIS side of the question, it is obvious that birds DO fly...... might look different if there were no birds.

Evan
05-18-2006, 06:47 PM
Ornithopters work just fine as long as the scale is similar to that of birds. Not a suprise, things we build are subject to the same physical contraints that evolution is. The history of attempts at powered flight is filled with efforts to make the wings do the work by flapping, pulsing, thrashing, flailing and rotating. Only rotating has ever worked but it requires a true rotary bearing, something that nature only uses at the bacterial size level.

BobWarfield
05-18-2006, 10:19 PM
The history of attempts at powered flight is filled with efforts to make the wings do the work by flapping, pulsing, thrashing, flailing and rotating.

I believe that list, flapping, pulsing, thrashing, flailing, and rotating, about sums up this particular thread.

;)

BW

alsinaj
05-19-2006, 10:52 AM
Don't know whether your approach will work for solar energy collection, but you are right to think about flexible materials. As machinists, we tend to think about rigid materials. Here's an example not so far from what you want to do. To provide one-size-fits-all eyeglasses for people in poor countries, someone invented flexible hollow lenses. The cavity is filled with saline solution. A small tube with a squeeze bulb can inject more saline, causing the lens to change shape. The wearer injects more or less saline, until he/she can see clearly. Voila! One pair of glasses that works for everyone in the village! Try that with rigid materials.

Evan
05-19-2006, 10:55 AM
Umm, I think the vacuum pulled mylar mirror concept also qualifies as non-rigid.