I keep following the thread on thermal power plants with interest, but I haven't posted in a long time due to repetitive arguments. Over time, I've seen quite a few misunderstandings of the physics involved in power generation there. To avoid that the technical aspects are overshadowed by the political debate, I started a new thread to cover the physics and engineering issues. In this post, I address the latest serious physics related error. Maybe more similar posts will follow if there is interest and I have some time to spare. A lot has gone wrong in the paragraph above. First, let's have a look at the basic physics of solar power. The most important value is the solar constant of I0 = 1361 W/m^2. That's the amount of energy per time that passes through an area perpendicular to the direction to the sun right outside of the earth's atmosphere. This intensity fluctuates by only about 7% throughout the year. As the light passes through the atmosphere, some of it is reflected, scattered, or absorbed. To get a rough idea of the various losses in direct irradiation, here is a picture of global averages. www.physicalgeography.net/fundamentals/7f.html In solar thermal power plants, the solar irradiation is reflected off mirrors and concentrated on a very black surface that absorbs most of the light. As a result, the absorber gets hot and that heat is used to produce pressurized steam that drives a turbine used to generate electricity. The machinery and the steam need to be cooled again to complete the cycle. So far so good. Let's have a look at the solar thermal power plant Silhouette was talking about. This picture was taken in the evening (from Google Earth). North is up and the sun was in the west. Silhouette claims that it's a very bad idea to use flat mirrors in this configuration. I disagree. Let's have a look at the geometry of this arrangement. The mirrors can be rotated around two axes to reflect the sunlight towards the absorber on top of the tower. The power reflected by a mirror with surface A is given by . α is the angle of incidence of the incoming and reflected sunlight. The angle between the direction towards the sun and the top of the solar tower is 2α. The following picture illustrates that the power reflected by the mirror is reduced depending on the incident angle of the light. Coalinga is at 36° N and the sun stands highest in the sky when it shines from the south. Since the angle in between the sun and tower as seen from every mirror should be as small as possible to maximize the efficiency, the mirrors are located to the north of the tower. There are about 3800 computer controlled mirrors reflecting the light towards the top of the tower. As a result, the the intensity of the concentrated light is much higher than the direct irradience of the sun.
Let's see whether flat mirrors are suitable to focus the light on the absorber on the tower. If the rays of light from the sun are parallel, the reflected rays are parallel too. The sun isn't a point source, however, and has a maximal angular diameter δ=0.545° as seen from the earth. This causes the reflected light to spread out. The following image shows a top down view of the situation. To visualize this effect better, the distance between the mirror and the absorber is reduced by a factor of 10 and the angle of the spread is increased by the same factor. This corresponds to a mirror at a distance of 537m, which is about the distance to the farthest mirror from the tower in Coalinga. All other sizes are to scale. As you can see, all the sunlight reflected off that flat mirror hits the absorber. This is true for (almost) all mirrors. In other words, flat mirrors work and the light is properly focused at distances below 500m. The additional absorption and scattering as the reflected light travels through the air is only a loss of less than 1% per 100m. Another claim made by Silhouette is that the absorber on top of the tower is essentially a tank filled with water with a high volume to surface ratio. This is not true, as can be seen on this aerial photograph taken for Google Earth. The absorber is pretty flat and there is no tank on top of the tower, only pipes for the pressurized steam. My conclusion is that the engineering flaws described by Silhouette turn out to be mere misunderstandings of physics and geometry. If I got something wrong, please point it out. Another interesting subject would be the role temperatures play in thermal power plants. As far as I can tell, there are some misconceptions related to that issue too. Finally, here are some links if you'd like to play around with the geometry of the mirrors and tower. Java is needed to run the applet. It asks for permission to execute and it might take a while to load. Enjoy. Geometry of the Coalinga Power Plant (distance reduced by a factor of 10) Geometry of the Coalinga Power Plant (to scale)
Nice post, thanks. Silhouette is upset because she can't figure out why this plant cost so much, and she's looking for a scapegoat. Since it can't possibly be the energy density issue, it must be something else, i.e., the engineering.
I am sure your geometry is perfectly correct. But I had to Google a Coalinga plant you are talking about. A solar plant to extract oil?!?! WTF?!?! That would have to be the dumbest idea I have ever heard. Why not just leave the oil where it is and use the solar array to do something useful like storing heat to generate electricity.
The reason, of course, is cost. The Coalinga plant, if converted to electricity, would never pay for itself. It probably won't pay for itself making steam either, but it looks nice in Chevron's "see, we're green" PR campaign.
Take the same amount of solar energy that falls on a flat circle and shine it on an closed container with thermoconducting material like metal. Inside that is water. Wait. See how long it takes for it to boil...lol.. Now, take the same amount of solar energy and make it concave. Focus it on the container with water. Wait. See how long it takes for it to boil. [with the second experiment, for safety's sake, please be sure to have a pressure-release valve on the container...unless you like backyard bombs. No worries with the first one though. ]
X amount of energy flux will take X amount of time to boil X amount of water, regardless of how it gets to the container, and regardless of what shape surface it is or isn't reflected off of. Basic physics, Sil.
You can think of the concave mirror as a collection of many small flat mirrors. The smaller you make the flat mirrors, the smaller is the difference between the round concave mirror and the one made out of many small flat mirrors. To assist your imagination, here's the picture of a paraboloid made out of many flat pieces. The many flat mirrors used to focus light on a central solar tower work in the same fashion. A very rough approximation is that every flat mirror provides a certain amount of power proportional to its size. So with 1000 mirrors you get 1000 times the light intensity at their focus compared to the intensity you get from one mirror. As long as most of the light reflected off the mirrors hits the absorber, everything is fine. In my opening post, I demonstrated that this is the case in the design the Brightsource engineers used in Coalinga.
I know, I know. You need some quick PR work on the net right? Somehow, some way you're going to "convince" people that shining a flat mirror on an anthill will somehow burn them out more efficiently than a magnifying glass, right? Sorry. We all know about the power of superheated steam. Didn't see any numbers in your calculations to explain the enormous distance you guys placed your ridiculously-large tank on that elevation tower..lol.. Oh...we didn't know about volume-to-surface-area ratios! Why animals in the polar regions and cold areas tend to be quite large internally relative to their skin size: so that the specific heat of their water-filled bodies will be more resistent to change from outside temperatures. Smaller internal volume in conducting tubes placed close to the concentrated sun energy = rapid heating to superheated steam. An entry-level physics student can cipher that one.
Let's have a look at the boiler used in Coalinga. Here's a nice picture: http://farm6.staticflickr.com/5215/5443076052_b349f7732d_o.jpg (high resolution) http://www.flickr.com/photos/abstractstv/5443072946/ As you can see, the black boiler is flat with a high surface-to-volume ratio (contrary to your claim). If you want to collect a lot of solar irradiation for a high steam output, you need a big mirror surface. In a design where many mirrors are focused on a single solar tower, distances necessarily get long since you obviously need to avoid placing mirrors in each other's shadow. Distance is not really an issue in this case because most of the light reflected off the mirrors hits the absorber despite the distance of up to 500m. Also, you seem to imply that I'm affiliated to the guys who built that solar tower. That's not the case. I am a physicist working for a small tech company that develops and produces microelectromechanical tools.
As you can see, it has a huge internal volume relative to the conductive surface. Flat sides, rounded sides, you're not fooling anyone knowledgeable about geometry, physics and chemistry. And I have a hunch that people who read this particular forum have more than a C+ level of highschool achievment in these sciences. Now study this design compared to the hugely inefficient Brightsource type: The elongated tube at any given strike-point of FOCUSED/MORE POWERFUL/CONCENTRATED solar energy has a much much higher surface area relative to the internal fluid volume. So the heating is rapid & powerful. Layer fresenel focusers along the top & parabolics shining back up at its base from the bottom and you'll have a turbocharged heating element the minute the sun shines. Ask yourself when it was the last time you had a flat mirror vitrify sand into glass or cut through steel? Because these are things that a concentrator does. There is no argument. Your mirror design falls..lol.."flat" on its face.
A concentrator reflects the power of the sun's light that hits its surface and focuses it on a small area. If the concentrater is large enough and the heat dissipates slowly enough, high temperatures can be achieved. The important thing to note here is that the amount of energy per time hitting the small spot in the focus is the same as the energy per time reflected or refracted by the concentrator (losses neglected). That's called conservation of energy. When building a solar thermal power plant the amount of energy collected per time is by far the most important value. The output power is proportional to the amount of light shining on the concentrators and therefore to their surface. Twice as many concentrators in the same arrangement give twice as much power. No matter how well a concentrator focuses the light, the total energy transferred is still determined mostly by its surface area. The operating temperature is regulated by how much water is fed into the system in relation to the power of the solar irradiation. First of all, let's calculate the volume V and surface S of a flat boiler with side length s and thickness t. The volume to surface ratio for thicknesses t much smaller than the side length s is approximately V/S = t/2. By reducing the thickness of a flat boiler you can get as little volume compared to surface as the material used allows at the desired pressure. It makes sense to choose a high surface-to-volume ratio to get efficient heat transfer. Moreover, the absorber needs to be as black as possible, the material needs to have a high thermal conductivity, the temperature gradient needs to be big, and the distance in between the working fluid and the illuminated surface needs to be small. On the other hand, the walls of the boiler have to be thick enough to withstand the pressure of the steam. Both a tube and a flat and thin boiler are suitable shapes to get a high heat flux. Concerning your design, Silhouette, I have some questions before I can address it. 1. What's the size of the fresnel lenses and parabolic concentrators? 2. How are the fresnel lenses mounted above the fluid tube such that they're able to track the sun and focus the light on the tube? 3. How do you address the problem that parabolic mirrors don't focus properly when used off axis at varying angles?
Golly! 10 whole MW since the 80s? Maybe that's because the tower is so freakin' far away from the reflected light and maybe that's because the imperfect design trying to mimic a concentrator by a circular pattern has too many flaws? And maybe if those mirrors were parabolic, the increase in heat in all those miniature suns might have a chance at overcoming the great distance between them and the target: a large interior-volume tank relative to it's conductive surface area. This poor design has many hurdles to overcome, or designed as inefficiency flaws right into its makeup, depending on what you're trying to achieve. 1. Too far from the fluid target. 2. Fluid target's conductive surface too small relative to the volume of fluid inside. 3. Flat mirrors don't achieve high temperatures like the chart above illustrates. 4. North-facing mirrors are superfluous and negatively affect calculations "proving efficiency" vs gross square footage of reflective surface. In short, the Brightsource design is retarded. After all, we're not talking about total solar energy reflected but about total heat that can be harvested effectively from that solar energy. Heat is, after all, the bottom line in solar THERMAL energy designing. The higher the superheated steam temperature and the more quickly that can be arrived at = the more MWs produced over a day's time. Concentrator/tube designs are superior because they increase the surface area of the conductive material surrounding the fluid, reltive to that site's internal volume. Focused sun rays reach astronomically-higher levels of heat temperatures so an array of them reflecting onto this elongated tube with high surface area equals rapid achievement of very high temperatures. In addition, the reflected "miniature suns" are much closer to the target. The Brightsource tower is hundreds of feet away from the flat/nonconcentrating reflectors! The Brightsource design is like a sluggish, cold-blooded dinosaur and the concentrator/tube design is like a hummingbird on crack. I contend the Brightsource design was done in such a way as to make solar thermal appear inefficient. Engineers knew back then how to achieve high temperatures by concentration of the sun's rays close to the source. After all, they all had tried as kids to light paper on fire with a magnifying glass. They all knew, the farther away you hold it, the less likely you'll get a fire and if you try the same thing with a flat mirror, you'll be there all day. And if you try the same thing with a flat mirror facing north and never reflecting the sun, then you're a drooling moron..! All those guys knew that. And they went ahead and designed the Brightsource design. Now you do that math...
That's a very nice introduction to solar concentrators. I recommend reading and understanding it. 10 MW is an amount of power generated. That's energy per time. It doesn't matter how many years the plant has been running, the yearly average power generated stays roughly constant given proper maintenance. There is NO large interior-volume tank in any of the solar tower designs I've seen. It's just not true and if you keep repeating that claim, you're destroying your own credibility, Silhouette. I've repeatedly explained this. I've shown an aerial and a ground based photograph proving that point. As further evidence, here's an image of the design of the receiver of the Solar One power plant the paper you quoted seems to refer to. Are there losses associated with using mirrors far away from the absorber? Sure. Those losses are relatively small though. The atmosphere is often very transparent to light. That's why we can see pretty far. Whenever it's not, for example when there's dense fog, no solar power plant works well in that area anyway. See above. There is no large interior volume tank as you've repeatedly claimed. A single flat mirror does not achieve high temperatures, but thousands of flat mirrors reflecting the light onto the same area do. The chart above actually supports my position. Central electricity receiver is listed as performing similarly well in terms of concentration and temperature as a parabolic electricity dish aimed directly at the sun. This is partially true, although grossly oversimplified. Since I'm curious about efficiency, I did some Matlab coding to find out more about the angle related losses. The following 4 maps show the energy collection efficiency of flat mirrors concentrating the sun's light onto a central tower in the Coalinga design depending on their location relative to the tower at the center and the season. North is up. The efficiency is compared to two-axis sun tracking parabolic dishes with the receiver in their focus (the best possible solution in terms of energy collection efficiency). If anyone is interested in the Matlab code used to generate those maps, I can upload it too. Here's the yearly average efficiency as an overlay over the aerial photograph of the Coalinga power plant. The mirrors in Coalinga are located in an area with about 80% efficiency or more compared to sun-tracking parabolic dishes. The question an engineer or investor has to ask now is whether that loss is worth it when compared to costs. It can be worth it to sacrifice some efficiency to reduce cost. Parabolic reflectors are unfortunately rather costly compared to flat mirrors and they also need a heat engine at their focus or some tubing to collect the heat and transport it to a central steam turbine (with some loss of heat).
Thank you for acknowledging that. The central "whatever" mounted way high on the tower is too far away. It is. Your target needs to be closer to the reflective surface. The strength is too diffused by the time it reaches your tower. Making matters worse, there is no concentration, only a 1:1 reflection of the sun's rays. If you think of the Brightsource design, it is trying to mimic a parabolic design by it's configuration of mirrors. But those mirrors are too far away. It's comical really how far away from the target that they are. Sure, they may gather a wider swath of sunshine in pure squre feet terms, but the setup is too expensive with gigantic flat mirrors vs smaller ones closer to the source. Thanks for making another point for me. Thousands of mirrors are way too expensive to install vs just dozens or a few hundred for the linear-tube solar thermal plant. Staying with my theory that the Brightsource type of arrangement is engineered to be either/or/and "too inefficient" or "too expensive per MW". And again, thanks for acknowledging that the Brightsource-type flat mirrors do not take best advantage for thermal production of energy by taking the same amount of sunfall and concentrating it to a potent "miniature sun" instead of just flaccidly reflecting a 1:1 heat value back onto the target. The attempt to mimic the real value of a perfect parabolic surface falls flat like a limp..well, you know.. It's like you're trying to get a girl pregnant by trying to hump her with your granfather's unit from 500 feet away! OK, thanks for the diagram. And it makes sense that they at least got the surface area ratio high enough with smaller tubes. I was thinking that if it was just a tank full of fluid, they would NEVER heat it up beyond lukewarm. And the "sense" that it makes, still staying with my theory is, that they had to engineer at least one component of the bogus setup to function properly. After all, the best ruse is one that "sort of works but is too expensive". If it didn't work at all, people, knowing it has in other countries, would say "wait a minute!..." When considering solar THERMAL [heat/temperatures] energy, the rest of your claims are deceptive and ignore the temperature chart I posted from the Harvard paper. Giant flat mirrors very far away from the source will never be as heat-producing at near-perfect concave ones close to the source. You acknowledge at least that using a long tube close to the source makes sense. Your heat calculations are dubious at best. For anyone considering investing in solar thermal energy, instead of getting confused by all the back and forth technical [which is also part of the ruse] just remember kids, "what fries ants on a Summer day better? A flat mirror far away or a magnifying one close up?" Consider the design not only with parabolics shining death-rays back up at the elongated tube, but also overlain on top of the tube by fresnel concentrators beaming downward on top of it. Andall much closer to the target, just a couple dozen or so feet away and all of those considerably smaller, cheaper and easier to install than the Brightsource design. The system takes up less space and produces more superheated steam more quickly and therefore more potential for MW. Invest accordingly.
That's a misleading statement. No one is suggesting to use a single flat mirror to concentrate the sun's light. The idea is to use a number N of flat mirrors reflecting the sun to the same area the size of about a single mirror such that the intensity in that area is N times the intensity of the sun. The interesting question here is why no one just uses one (or a few) sun-tracking big parabolic mirrors, although they offer the highest energy collection efficiency. The parabolic mirror is relatively simple to build in the small scale, but the problem is that it doesn't scale well. Building large parabolic dishes is a costly and difficult engineering challenge. Massive support structures are needed such that the dish can hold its own weight and withstand some wind. As an example, here are two radio dishes of the Very Large Array used for radio astronomy. Those parabolic dishes are 25m in diameter and could concentrate the sun's light efficiently to a small area. They look cool too, but they're just too costly. That's where the idea of using many smaller sun-tracking mirrors comes in. By using, for example, 4 by 4 meter flat mirrors, you need 31 of them to get the same effective surface area of 491m^2. Those 31 small mirrors are much easier and cheaper to build than a single big one. This design is easily scalable by adding more mirrors and the light concentration factor increases with the number of mirrors. How is the strength diffused and by roughly how much? Why do the light rays significantly diverge from a straight path? Linear solar thermal plants are less efficient per mirror area because they track the sun only along one axis. I am aware of your design, Silhouette, that includes two axis tracking, but this isn't really linear. The parabolic reflector and fresnel lenses focus the light only on a few spots along the length of the tube in the middle. In other words, you have all the trouble of two axis tracking, but don't really gain anything by focusing on a tube. I've addressed that one before. N flat mirrors reflecting the light on the same area result in a N:1 concentration ratio, not 1:1. It's good to see that you noticed this picture. Your conclusion is interesting too, although rather far-fetched. I don't know why you call anything I wrote deceptive. I did not ignore the temperature chart. Here are the relevant entries: Code: Type Sun's Tracking Capability of Type of of Lens or Concen- Tracking Receiver Temperature Typical Concentrator Focus Mirror tration (yes/no) (yes/no) ([degrees] C) ([degrees] F) Applications Comments Parabolic point mirror > 1000 yes yes >2638 >3000 electricity Small-scale applications dish two-axis heat Central point mirror > 1000 yes no >2638 >3000 electricity Large-scale applications receiver two-axis heat Parabolic line mirror 100 yes no 538 1000 electricty Can be used for both small and trough one-axis heat large systems Parabolic dishes and central receivers provide higher concentration ratios and temperatures than linear designs. By the way, I encourage everyone to check and question everything I'm writing. In that spirit, here are links to the Matlab code used to generate the efficiency maps. solartower.m (returns efficiency matrix for one day) solartoweryear.m (plots efficiency maps for 4 seasons) Parameters: l.. latitude (from -pi to pi) s.. season (location of earth on its orbit, 0 is spring, pi/2 is summer in the north, and so on...)
Which is precisely why Brightsource design isn't a go. It is, in effect, an attempt at a gigantic parabolic mirror. Hence the circular configuration all pointing at a central point. It is large, unwieldy and inefficient for the cost of construction. It comes with the added downfall of since Brightsource went "huge" parabolic, it has to locate the reflectors at too-far a distance from the target. Smaller parabolics lined up along a linear tube make more sense. Making more sense still is to overlay that tube design with fresnel lenses, amplifying even more the quick-heating potential to superheated steam in the tubular design. They're getting built around the world as we speak..sans the fresnel overlay. But I believe it won't be long before this innovation will be part of the construction. So Herby, you're right, the very very large parabolic design of Brightsource is too unwieldy and expensive for the MW produced. Better to scale them down, like you said. Then array these "miniature suns" along the length of the tube, located much closer to the focused rays, then off to the heat exchangers like any other steam-driven turbine power source..
You didn't calculate (*)(*)(*)(*) you googled the answer. If your trying to find the volume of the "concave mirror" posted you use an antiderivative. The function f(x) as far as I can tell looks like x^2, thus y = x^2. Since we want to integrate on the y axis, x = Sqrt(y). And when dealing with volume we use pi * (integral, from a to b)[R(x)]^2dx Since there is no specified width we will take an indefinite integral of pi(ydy) = (pi*y^3)/3 + C
This is certainly the most colossally dumb thing you've ever said here -- and that's saying a lot. A lens in front of the parabolic trough means no light gets to the trough. The lens focuses light directly on the central collector, where it is absorbed. Hence the cost to build the trough is wasted. You've just doubled your cost for no reason. I'd also like to mention that fresnel lenses are likely to be much less efficient that the mirror trough. Since they're flexible, the focal point moves (and de-focuses) with the wind. The larger the lens, the worse this problem gets. Odd, since just the other day you were touting large-scale solar-thermal plants as being a good idea for "a centralized power plant like we are used to." A plant that size -- say 1 GW, which is typical of large coal and nuclear plants -- would require at least 1 square km of collector area. That's about 250 acres. And that means a loooong way to run a pipe full of hot water without losing most of the heat in transit. Plus, you get a power plant that won't work at night, won't work in cloudy weather, and is highly vulnerable to severe weather like hail and high winds. Can we agree now that solar thermal is useless for large-scale power?
Try to keep up, AT. The volume calculation was for the thermal collector, not for the mirror. Since the mirror in this case is flat, it's volume is effectively zero.
The fresnel lenses sit atop the tube, just. Not atop the parabolic troughs. Look at the design at the top of last page. It's a bit hard to tell but the "side view" picture has lines above the target tube. Those are the fresnel lenses/magnifiers and they don't obstruct light to the troughs at the sides and underneath the tube. The point is that Herby inadvertently made himself is that the Brightsource design is a crude attempt to mimic a parabolic reflector on a grand scale. But the scale is too grand meaning the individual flat reflectors are [must be due to their size/expense] located too far from the focal point. Since heat energy is what we're talking about reflecting, that great distance will result in too great a loss of heat by the time the focal point is reached. Putting smaller/cheaper parabolics closer to the target preserves the potency of the focused heat as it only travels a short distance to the conductive surface.
Finally, I understand why you keep worrying about distance, Silhouette. Those mirrors reflect light though, not heat. For the length scales we're talking about here, light rays travel in a straight lines to a high degree of precision. The light isn't converted into heat until it hits the absorber. The most relevant deviation from light traveling in straight lines in this situation is caused by the air. After traveling many kilometers through the atmosphere adding another 500m of air to scatter in only makes a small difference though. With the exception of cloud coverage, very high humidity, or more unusual aerosols like smoke, the air isn't a big problem. Lens and mirror are interchangeable. You can choose one, but can't have both to cover the same area of incident light. Since it's possible to tightly pack both mirrors and lenses, I don't see a good reason to use both. Here's a cross-section through Silhouette's design as I understand it. In this case, the green lens could be replaced by the green reflector segment behind the focus.
Yes, exactly. And this is why near-surface agitants impeded the efficiency of the Brightsource design, on top of the bigger you spread out individual facets of your parabolic array [which is what central-tower Brightsource designs try to imitate on a grand..and inefficent...>your words<...scale]. High up in the atmosphere there are less agitants like dust, pollen, moisture, smoke and so on. Not that those don't exist high up, just that near ground level [where the Brightsource flat mirrors are] you have the highest concentration. So over a distance of hundreds of feet, typical of the distance between the Brightsource flat mirrors and the tower focal point, you have a significant loss of heat. Add to that the fact that no mirrored surface can be kept spotless, including the tube arrays from concentrated solar heat. This means that there really isn't a 1:1 reflection ratio of incoming solar rays with the flat Brightsource mirrors. Instead it is diminished from that unless the reflectors are polished to a sheen, every single one, every single day...better if twice a day actually. And we know that's not happening... When you concentrate solar heat with parabolics and you keep them close to the target, the heat loss is extremely mitigated by the fact that the concentrated heat beams are so hot, even with imperfect reflective surfaces, that if the tubes were any closer, the beam may start to cut through the steel. That is maximum efficiency in heat-capture. Well not quite. If you overlay the elongated tube with fresnel concentrators [and no, they don't obscure the parabolic reflectors below] you have the most efficient solar thermal system I personally can think of. But that surely doesn't mean someone else doesn't have an improvement on that. For instance, if you can somehow get the concentrators closer to the target without jeopardizing the conductive material of the tube, then superheated steam can be achieved even faster. The Brightsource design is like a sluggish and expensive dinosaur, engineered to underperform as to solar thermal's true potential. BigOil has been doing this forever: creating sham efforts at green energy to portray it as weak and inefficient. I used to giggle at the Brightsource design thinking it was just poor engineering. But when I saw that Chevron had teamed up with Brightsource on the same design I knew in a moment that that particular design was engineered to underachieve.. to "prove we still need oil" to run the joint. There's a design for wind energy that isn't being used that is more efficient too. I don't have the time to develop it but I'll give a hint: it's in plain sight nearly everywhere you look. Just look. Look. The design already exists. It's just that nobody has harvested it. The big unwieldy prop designs are not it.
