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| 2008/6/20-23 [Consumer/TV] UID:50315 Activity:kinda low |
6/20 http://www.engadget.com/2008/06/20/mit-solar-dish-holds-promise-for-low-cost-energy-production MIT STUDENTS RECREATE DEVICE FROM 4000 YEARS AGO THEY MUST BE GENIUSES \_ If you are referring to Archimedes' supposed defense of Syracuse, that was about 2200 years ago, not 4000 years ago. And most people think that the story is untrue (mythbusters ran a piece on it a few years ago). \_ MIT recreated the stunt right after that episode was aired. they did it using $1 mirrors. So, Mythbusters proof on TV > actual demonstration? You watch too much TV! http://tinyurl.com/yu7e5x \_ Actually I have never seen an eps. of mythbusters. Wikipedia mentioned the eps. re Archimedes, which is how I knew about it. In any event, I think it is still an open question if this would work against a non-stationary target. \_ You should. It isn't good science but it is amusing. \_ What is the important thing about this dish? Clearly the basic idea of a concentrating dish is pretty ancient and the blurb didn't go into what is unique here. \_ "Another standout feature of the dish is its small size, and furthermore, the material required to build it is relatively inexpensive and accessible worldwide" \_ Still not sounding very interesting to me, sorry. |
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| www.engadget.com/2008/06/20/mit-solar-dish-holds-promise-for-low-cost-energy-production The company's name is RawSolar, and in due time it could end up selling solar dish arrangements that could power factories or even heat / cool office buildings. Recently, a team of students and faculty celebrated as a prototype dish proved that it could concentrate sunlight by a factor of 1,000, which obviously bodes well for converting that into useful energy here on Earth. Another standout feature of the dish is its small size, and furthermore, the material required to build it is relatively inexpensive and accessible worldwide. Sounds like all the ingredients for a successful startup are there, now we've just got to wait and see if anything becomes of it. Jun 20th 2008 9:21AM Because it would burn a hole through it. This type of solar concentrator is normally used in conjuction with a water/steam generating system. Though I have not seen one small enough that would work with this. However I am sure that is what they would be working on. Jun 20th 2008 9:17AM @Don Corleone Silicon and heat don't mix all that well. Solar Collectors are used sometimes to make the concentration of a specific wavelength of light more efficient, or to just increase the amount of light avaialble, but a design like this one is probably aimed at generating heat. By superheating something like water you can make steam and use the steam to drive a generator. Or heat a pool, or your office, or the backside of your jeans (remember the magnifying glass prank from grade school).. Jun 20th 2008 9:18AM Because the heat generated would reduce the output, and it is likely if you can burn a 2X4, you would destroy the panels. However, a lot of people are using small lenses on solar panels to get a slightly higher output. Jun 20th 2008 9:27AM Let's just say that you wouldn't damage the PV panels you were pointing at... The efficiency of PV will drop about half a percent (from posted STC rating) for every C over 25C. Jun 20th 2008 9:16AM This strikes me as a very bad idea. I imagine any unfortunate bird would be fried instantly should the accidentally fly over one of these things. Not to mention the abundance of "Darwin award" winners should these things ever get out in public. I can already see the headline "Man incinerated while trying to clear dirt off his solar dish". Jun 20th 2008 9:21AM I think there are enough birds in this world that the occasional cooked sparrow isn't going to threaten the existence of the species. As far as the Darwin award goes, there are a million and one ways to hurt yourself in this world, doesn't mean we shouldn't have things that might be able to hurt us around. Idiots and animals, are for the large part, disposable to society. Not to mention that a solar array is a lot safer than burning coal. If some kid manages to burn his head off once every year then thats a lot better than millions of people eventually getting lung cancer or empheseuma because of pollution. Jun 20th 2008 11:07AM Actually for much of the developing world generating heat for cooking is the major problem. I'm sure once their 50" Plasma TVs arrive they will become interested in electricity. Unlikely to be fried instantly (or even baked instantly) - just as your hand is not baked instantly if you happen to touch a flame (which has a higher temp than this will generate). Jun 20th 2008 9:19AM Solar collectors/concentrators have been around for many, many years. The innovation here is not the concept, but the manufacturing process and efficiency of light gathered. You can buy them from catalogs as portable grills, pool heaters, alternative water heaters, magnifying glasses, fresnel lenses, etc, etc,etc,etc,.. Jun 20th 2008 9:21AM I wonder if one of these could heat up a hot water heating system here in the north, the type that runs water tubes through a slab. Heat the water during the day and the slab holds the heat until the next day. My parents have a slab system that runs off of LP and it's about the nicest feeling heat you can get. Jun 20th 2008 9:36AM They are called Thermal Energy Storage solutions or TES. They are used primarily for cooling but conceptually it is similar. You use the off peak power (or free power such as solar) to create energy which is then stored in some container. In cooling systems you literally freeze a large block of typically water and some chemical and then use that block of ice during the day during peak hours to provide cooling. Work is just starting in heating systems but there are examples of this in commercial production as well. Jun 20th 2008 9:38AM they already have professional companies doing these dishes but their expensive because of the mirrors etc.... my idea would work better and be made for A LOT cheaper... a properly molded and tuned standard satellite dish..... Jun 20th 2008 9:55AM Sweet, now thats one hell of an idea. I would get one for my house if I could afford such a thing. Any way to cut bills and emissions would be someone to be proud about. At least I know I would be doing my part to help fight the cause. Jun 20th 2008 10:13AM I'm glad someone mentioned Rob's "Cockeyed" website. Aside from the 'prior art' I like the form of the MIT dish, it looks very light and still rigid. Jun 20th 2008 10:25AM Just looked for more specifications on how this was done without much luck. I then looked for flexible mirrors and found a couple of sources -- funhouse mirrors and children's mirrors seem to predominate. It would take only a bit of work to compute a cutting pattern to fit the mirror onto a parabolic frame. With about 4 of these sheets one could have a 4'-square (approximately) mirror without having to wait for some special supplier as they (apparently) did. The downside seems to be that these flexible mirrors are not designed for long-term weather exposure. I suspect some UV coating on the front and some epoxy or other coating on the back would make them last a long (enough) time. Having to replace the surface every few years would not be a huge burden. Another thought -- how about getting an old satellite dish and gluing small mirrors to it? Already comes with the hardware to position it -- just add a tracking module. Jun 20th 2008 11:43AM UNLV in Las Vegas has had two of these operating for years - they move and track the sun automatically, and generate energy by focusing the sun on a Stirling Cycle engine. The principles of sunlight concentration have been known since antiquity, and low-cost solar cookers have been used since decades, esp. in areas in Africa where wood was becoming dangerously scarce. I would be much more interested to see how the geniuses at MIT are going to convert this heat into something more usable. They're not going to cook their potatoes on it, are they? The Stirling engine comes to mind if you want to convert heat into motion. Or they could split water molecules into hydrogen and oxygen. E-Mail me when someone replies to this comment Add your comments: Add Your Comments Please keep your comments relevant to this blog entry. Email addresses are never displayed, but they are required to confirm your comments. When you enter your name and email address, you'll be sent a link to confirm your comment, and a password. To create a live link, simply type the URL (including http://) or email address and we will make it a live link for you. 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| tinyurl.com/yu7e5x -> web.mit.edu/2.009/www//experiments/deathray/10_Mythbusters.html read about and see video of the original experiment at MIT in 2009. On Friday, October 21, 6 students from the current and previous two years of 2009 and the course instructor went to San Francisco to burn a real boat with the MythBusters. October 21 was used for final mirror fabrication and to setup the stands for the array. condition after On Saturday, October 22, the weather was good. We were able to cause charring and smoldering in a 1-2 foot wide swath along much of the boat's length. After three passes over the boat, the hull was penetrated and a small open flame was achieved. high moisture content of the boat that was used as a target. In my view, it is an open question as to whether the boat was representative of a seaworthy Roman ship... but at least this boat should not be considered as too easy a target! first MIT test as a benchmark and accounting for the different mirror material, along with the different conditions in San Francisco. The tiles were polished using Brasso by the MythBuster and MIT team. About 30% of the mirrors had a variety of flatness defects that would reduce their performance to some degree. The tiles were aimed in a manner similar to the MIT test, with the exception that there were 4 tiers of mirrors instead of just two rows. The mirror array was about 110 feet long, similar to the MIT test. The goal was to make an array that was big enough to start a fire, but small enough to implement within reasonable budgetary and time constraints (my guesstimate is 3-4 person weeks, mostly spent on polishing the bronze). Our understanding was that the target boat was a 30 foot, 1924 wooden fishing boat. It was purchased from its prior owner after it had sunk and then been retrieved and brought back to port. We were told that it was much lower in the water before the engine and other heavy items were removed a few days before the test. It is believed that the boat planks were made of douglas fir. The planking was estimated to be 2-3 inches thick, dependent upon location. The boat had been partially stripped of paint and then coated with pitch. The boat was positioned so that it was roughly 150 feet from the center of the array. Since the array was in a straight line along the edge of a dock, the furthest mirrors (at the ends of the array) were roughly 160 feet from the boat. The test began at roughly 12:15 and the 300 bronze mirrors took 10 minutes to aim (14 people working in pairs) using an aiming process similar to the MIT experiment. The aiming mirror was initially pointed at the stern of the boat since the motion of the the earth around the sun caused the point projected by the fixed mirrors to move towards the bow of the boat over time. Almost immediately after uncovering the mirrors, a considerable amount of smoke was visible. Black charring was visible on the side of the boat in a few minutes. The bright spot was estimated to be 4-5 feet in diameter... not as tightly focused as we had anticipated based on preliminary tests, but not terrible either. As the sun spot moved along the side of the boat (at about 9 inches per minute), it created a roughly 1-2 foot wide charred band along the side of the boat, but without open flame. We believe that a significant amount of moisture was being boiled out of the wood. When the sun spot had moved to 3/4 along the length of the boat (leaving an estimated 20 feet long x 1-2 feet wide charred strip on the boat), we attempted to continually adjust the position of the mirrors to keep the bright spot on a single location, giving the wood more time to dry and heat. In doing so, we were not able to keep a focused beam, and the bright spot became much larger, reducing the power per square foot. At roughly 12:40, we repeated the process, again using the bronze mirrors. The targeting mirror was aimed at the stern of the boat and the entire array was re-aimed. This allowed us to make a second pass over the band partially dried and charred in the first attempt. There was an even more substantial amount of smoke and the charring deepened. The beam was better focused than the first attempt (3-4 feet in diameter). There were glowing, smoldering embers in a number of locations along the side of the boat, and in some locations there was white ash on the surface of the planks... After letting the beam traverse the length of the boat it was requested that we try to ignite a sail, again using the bronze mirrors. This created a bright spot on the sail and no charring whatsoever. During the time that the beam was focused on the sail, charred areas on the side of the boat continued to smolder. After the test with the sail, we decided to switch to silver/glass mirrors to see if they could take us from smoldering embers to open flame. The silver mirrors provided a tighter beam that we could more easily focus (2-3 feet in diameter). We repeated the process, making a third pass along the side of the boat, starting with the aiming beam at the stern of the boat, and letting the bright spot move its way along the side of the boat (again, at roughly 9-10 inches per minute due to the motion of the earth). There was substantial smoke, and at one point near midship, there was a period of near-calm wind. The smoke pattern looked very much like what we saw just prior to flash ignition in the test at MIT However, no open flame appeared, even though there were substantial glowing embers. At this point, we decided to bring the boat closer for one last attempt to achieve open flames. The rationale was that, at a shorter distance, we would be able to more tightly focus the beam. It would have been better to use the time to just make another pass over the boat since, as became apparent later, the coals were on the verge of reaching an open flame (the glowing coals can be seen right under Jamie's feet in the picture at left, which was taken while the boat was being repositioned). Regardless, we brought the boat to a distance of 75 feet and began the aiming process once again, starting from the stern using the silver mirrors. However, while the beam was still near the stern, a modest open flame broke out mostly on the inside of the hull at midship, near a scupper hole. The sea breeze was really picking up and presumably fanned the burning embers to obtain an open flame. The open flame was caused by the efforts at 150 feet since the beam at the closer distance had not yet reached this point on the boat (Jamie pointed this out to us when the flame broke out). It is not clear if the switch to silver mirrors was necessary. Before the closer range beam reached the burning area on the boat, a substantial wind gust blew over several of the mirrors, creating a rather spectacular effect and ending the experiment. We had modeled that this would occur when the winds reached 14-15 knots. We did not have the instrumentation needed to obtain a wind speed measurement. Thus, we could not make a comparison with our estimated value. We had planned to finish before 2 PM and thereby avoid the afternoon period when the sea breeze becomes quite strong. The fire at midship continued to smolder with glowing embers and also intermittently burn with open flame. Open flame appeared to be dependent on fanning by the wind. About 2 hours after ending the test, the fire was still smoldering with intermittent flame. There was a roughly 10 inch diameter hole in the side of the ship. Final thoughts: We were able to cause charring and smoldering along the length of the ship. After three passes along the boat, we were able to penetrate the hull in one location and achieve an open flame. This burning area was self-sustaining as a smouldering fire, and about 2 hours after the test had ended it was still burning and had created a roughly 10 inch hole in the boat. We were not able to achieve the large flash ignition as we did with the 2009 experiment at MIT Most likely, the difference was the moisture content of the wood, which was very high. Certainly wood in any boat on the water would have higher moisture content than kiln dried lumber but, given the history of the boat, it may still be an open question as to whether the moisture content (above the... |