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The dish is composed of a set of 10 inch by 12 foot curved mirrors, like the one seen here. The students easily mount the mirrors to the aluminum framework using simple hardware like washers and zip ties.  (Source: MIT)

The mirrors incredible power makes short work of a beam of wood, disintegrating it in flames and smoke. The focal point can melt steel.  (Source: MIT)
New solar dish from MIT concentrates sunlight intensely enough to melt steel

The solar industry is booming.  With waves of investment and grants, the solar power industry is for the first time becoming a serious business.  New power plants will soon be pumping power out to consumers, while other firms market to sell panels directly to the consumer, providing them with a more direct means of experiencing solar energy.

There are many forms of solar power technology.  Today the most dominant is photo-voltaics, which comprise the traditional solar panels that come to mind when one thinks of solar power.  However, there are other promising ways of capturing the sun's energy that are merely less developed.

Among these is a parabolic collector.  A parabolic collector consists of an array of mirrors focused on a singular point, which they heat to a high temperature.  By placing water or another liquid at the collector, energy can be stored in the form of a phase transformation, and later harvested through a turbine generator.

However, parabolic collectors are still a relatively new field of research.  Their true potential remains relatively unknown.  A glimpse of it was provided by a research team at MIT, which developed a new parabolic collector design, which will blow away current solar power designs in terms of efficiency.

The MIT team believes that their lightweight, inexpensive device holds the promise of revolutionizing the power industry and providing solar power to even remote regions.

The key piece is the 12-foot dish, which the team assembled in several weeks.  The design is exceedingly simple and inexpensive.  The frame is composed of aluminum tubing and mirrors are attached to it.

The results are staggering -- the completed mirror focuses enough solar energy at its focal point to melt solid steel.  The energy of typical sunlight is concentrated by a factor of 1,000.  This was showcased during a demonstration, in which a team member held up a board, which instantly and violently combusted, when brought within range of the focal point.

By directing the dish at a more practical target -- water piped through black tubing -- steam can be flash created, offering instant means of producing energy or providing heating. 

Spencer Ahrens, who just received his master's in mechanical engineering from MIT, was among the designers of the dish.  He and his fellow team members are serious about marketing it, and leveraging its cheap cost and easy production.  They have founded a company named RawSolar.  They say their design is easily mass producible and that they hope to be pumping out 1,000 of dishes in years to come.

The new dishes would return their costs in a mere couple years, unlike standard photo-voltaic installations which can take 10 years or more to return their costs.  This improvement is critical to providing practical economic justification for adoption.

The dish is based partly on components invented and patented by inventor Doug Wood.  He was so pleased with the team's work that he signed over rights to the components to the team.  He elates, "This is actually the most efficient solar collector in existence, and it was just completed.  They really have simplified this and made it user-friendly, so anybody can build it."

Wood says one of the keys to the success of the project is the smaller size.  Dishes are affected by the same weight dynamics that effect living organisms.  Much as large living organisms would need an inordinate amount of weight support and thus are not favored, larger dish designs fall short in that they require an exponentially greater amount of infrastructure.  For example, a dish the size of the RawSolar team's design costs only a third of what a larger dish would cost.

MIT Sloan School of Management lecturer David Pelly gave a guiding hand to the students and thinks the economic upsides of the technology are impressive.  He states, "I've looked for years at a variety of solar approaches, and this is the cheapest I've seen. And the key thing in scaling it globally is that all of the materials are inexpensive and accessible anywhere in the world.  I've looked all over for solar technology that could scale without subsidies. Almost nothing I've looked at has that potential. This does."

The ability to build unsubsidized, profitable, and easy to manufacture solar power will truly be something amazing.  This should be an exciting technology to follow as it is marketed and further developed.

Besides Ahrens, the other students primarily working on the project were Micah Sze (Sloan MBA '08), UC Berkeley graduate and Broad Institute engineer Eva Markiewicz, Olin College student Matt Ritter and MIT materials science student Anna Bershteyn.

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RE: Mythbusters
By trajan on 6/21/2008 4:45:26 PM , Rating: 5
Nahh.. If I remember the myth of Archimedes, it was that he burned Persian ships out at sea from the shoreline. Building a parabolic mirror that can incinerate wood at a short distance is nothing new, but doing it at a range of half a kilometer or so -- that would be impressive. THEN, try doing it using bronze or other materials available to the ancient Greeks.

If the MIT device is novel, its only because its cheap to build and relatively high efficiency, both of which are very important for the future of solar energy.

RE: Mythbusters
By Goty on 6/21/2008 7:17:38 PM , Rating: 3
If the collecting area remains unchanged, all you have to do is change the focal point of the mirror.

RE: Mythbusters
By freeagle on 6/21/2008 7:49:16 PM , Rating: 3
but focusing several mirrors on a close-range focal point is way easier than focusing on something several hundreds meters away

RE: Mythbusters
By Goty on 6/21/2008 9:18:11 PM , Rating: 3
Well, yeah, it's easier, but that doesn't mean long-distance focusing isn't possible.

RE: Mythbusters
By Flunk on 6/21/2008 9:51:59 PM , Rating: 3
You forget, the technology to create curved mirrors did not exist so the point is mute.

RE: Mythbusters
By drank12quartsstrohsbeer on 6/21/2008 10:38:26 PM , Rating: 3
i think 'moot' is the word you are looking for. And how do you know that curved reflectors could not be produced? they most certainly had the technology to make a curved reflector.

RE: Mythbusters
By omnicronx on 6/27/2008 9:03:04 PM , Rating: 2
And how do you know that curved reflectors could not be produced?
Mirrors were not known to exist for 800 years after Archimedes 'apparently' created this death ray. Its pretty hard to believe that not only did he have something that did not exist(mirrors), but he also figured out how to curve the them. Seems pretty unlikely to me.

RE: Mythbusters
By masher2 on 6/21/2008 11:32:08 PM , Rating: 3
> "You forget, the technology to create curved mirrors did not exist so the point is mute"

You don't need a curved mirror to build a parabolic reflector; you simply need a large number of flat reflective segments, arranged on a parabolic surface...something which the Greeks certainly knew themselves.

RE: Mythbusters
By TheBaker on 6/22/2008 12:35:02 AM , Rating: 2
Yeah, but if you don't use curved mirrors you get a "stack" of flat panels of light, rather than a true parabolic reflector.

That is, the energy is focused into a (for example) 12" x 12" square rather than a 1" x1" (or smaller) area. The energy in the large square would make something really hot, while that same energy in the small square would be 144 times more powerful, and would burn things to a crisp. Make it a true parabola and the energy is condensed to a point source. Eventually, you get what these kids at MIT came up with.

They didn't do anything new, they just did it with more precision and efficiency than before.

RE: Mythbusters
By masher2 on 6/22/2008 12:46:14 PM , Rating: 5
Even a mathematically perfect parabolic reflector won't focus to a light to a single point. The minimum focus size is defined by many factors: aperture (size) of the reflector, wavelength of the reflected light, visual size of the sun or other psuedo-point source, etc.

So in reality, nothing is a "true"parabola. If a stacked mirror such as this contained, say, 1000 flat segments, the intensity at the focus could be as strong as 500X normal solar flux....certainly hot enough to ignite wood.

RE: Mythbusters
By blue7053 on 6/26/2008 6:48:06 PM , Rating: 2
The embarassing thing about this is the number of people who are amazed by it. 'The kids' at MIT didn't do it, some guy in Iowa did it and showed them where to buy 12' mirrors. There is absolutely nothing new here except the knowledge of the melting point of steel. Even there, they don't enumerate it. They just wave in the general direction.

RE: Mythbusters
By achintya on 6/22/2008 1:54:23 PM , Rating: 3
Yeah, but after a point, if you scale the piecemeal 'parabolic' mirror up it slowly starts achieving the shape of a true parabola. Basic geometry. Even a polygon with enough sides starts looking something like a circle. Think of a polygon with over 20 sides. Looks enough like a circle anyways. Most new large telescopes are made the same way by assembling many small straight pieces.

RE: Mythbusters
By someguy743 on 6/22/2008 3:39:16 PM , Rating: 2
Wow, this new solar thermal technology really could be revolutionary. I'd like to know what the "solar to grid conversion efficiency" number is for this solar thermal dish. Stirling Energy already makes a larger sized one that looks similar. It set the record for efficiency at 31.25%:

If Raw Solar's solar dish is a lot more efficient than Stirling Energy's AND it is a lot cheaper to manufacture and deploy in the field then these MIT guys might be sitting on a gold mine. Big Coal and the other fossil fuel industries won't like this one bit. :) It really could reach and exceed the price per kilowatt that coal is now. Now ... if only the solar thermal industry can get some really cheap energy storage technology to come out, they've got the world by the tail.

Cheaper energy storage and cheaper transmission lines are all that's standing in the way of solar thermal, photovoltaic and wind from becoming the dominant energy sources in the next 20 years ... in a super efficient and flexible "smart grid". I bet it's going to happen. The dream might soon be realized. Inexpensive, inexhaustible, non polluting clean energy that will NEVER run out and cannot be manipulated nearly as much by the Wall Street schemers and Big Oil, etc. :)

RE: Mythbusters
By masher2 on 6/22/2008 3:54:04 PM , Rating: 3
> "Stirling Energy already makes a larger sized one that looks similar. It set the record for efficiency at 31.25%:"

Concentrating solar cells already exist which have efficiencies in excess of 40%. They're still far more expensive than coal or nuclear.

RE: Mythbusters
By Denithor on 6/23/2008 9:00:44 AM , Rating: 2
Inexpensive, inexhaustible, non polluting clean energy that will NEVER run out and cannot be manipulated nearly as much by the Wall Street schemers and Big Oil, etc.

...which is exactly why it likely won't happen for several years.

RE: Mythbusters
By jskirwin on 6/27/2008 3:50:36 PM , Rating: 2
Inexpensive, inexhaustible, non polluting clean energy that will NEVER run out and cannot be manipulated nearly as much by the Wall Street schemers and Big Oil, etc.

Electricity gets manipulated all the time by Wall Street schemers (Is that what some call investors nowadays?) Enron did it to California in 2001.

RE: Mythbusters
By blue7053 on 6/26/2008 7:11:25 PM , Rating: 2
I don't know whether this is new or not, nevertheless I worked it out 20 years ago. Showed it to a country neighbor once, he said, "Oh yeah. I read about that in a magazine."

Forming the Greek parabola:
Start with a 4x8 sheet of plywood, drive a nail in lower left corner of the long side.
Tie one end of an 8' string to the nail, double the string, (now 4') and put your pencil in the loop of the string.
Hold one end of the string at the nail and the other end with the pencil at the upper left side of the plywood.
Move the free end of the string along the bottom side of the plywood and the pencil to the right, maintaining a right triangle relationship between the nail, the pencil and the free end of the string.
As you move the pencil and the free end of the string to the right, you will be drawing a curved line describing the point of the opposite side and the hypotenuse. As the opposite side of the triangle moves away from the nail, the opposite side diminishes as the base and the hyoptenuse increase. The relationship amoung the sides remains constant.
When you end up with your 8' string at the lower right corner of the plywood, you will have half a parabola described across the sheet of plywood. The focal point is the nail.

RE: Mythbusters
By lco45 on 6/23/2008 4:07:22 AM , Rating: 2
A stack of flat mirrors is the same as one curved mirror, if you know your calculus.

A curve is just a bunch of straight lines, with the length of each line tending towards zero.

The greeks understood calculus, although not to the degree the Newtonians took it. Google "squaring the circle" for info on an early greek take on calculus.


RE: Mythbusters
By masher2 on 6/23/2008 11:24:17 AM , Rating: 2
More precisely, a curve can be considered a set of infinitely short line segments. There is a difference between a stack of flat mirrors and a curve...but that difference tends to zero as the size of the mirrors decreases.

And 'squaring the circle' isn't calculus. It's the equivalent problem to finding the area bounded by a curve, a problem which can also be solved by integral calculus..

RE: Mythbusters
By mpc7488 on 6/22/2008 12:16:18 AM , Rating: 4
Did you guys watch the actual show? They dealt with a lot of these questions after they had the first show, then invited MIT back for the re-visit.

It wasn't the distance itself that made it fail, it was the fact that the ship was moving. Even a slight shift brings it outside the focal point, which requires re-alignment (not trivial at all), in which time it's moved again, etc. It was pretty neat to watch them make the ship smoke though, even if they couldn't ignite it in flames.

RE: Mythbusters
By masher2 on 6/22/2008 12:37:22 PM , Rating: 2
> "It wasn't the distance itself that made it fail, it was the fact that the ship was moving"

But of course, in the time of the Persians, attacking ships would not have always been moving. In this day of motorboats and jet skis, people forget that ancient ships could not move against wind and tide. You couldn't simply sail (or even row) into any harbor whenever you wished; you needed conditions to be right.

The normal process was therefore to approach a harbor, then anchor until tide and/or wind was favorable for entry.

RE: Mythbusters
By tmouse on 6/24/2008 9:43:33 AM , Rating: 2
I guess you did not see the show. The MIT group tried and totally failed. The materials available at that time (bronze) was far inferior to silvered glass, the ship was rock steady in their tests in a calm bay slip, not the ocean; even bringing it in to 50 feet just got a slow smolder (this was a VERY dry old ship, not one that just made a voyage and would have been far damper). Add to this Syracuse faced east limiting the use of the weapon to the weaker morning rays and the availability of other more practical fire based methods and it seems very implausible. Even historically; it took 300 years to even mention that fire was used in the battle and the use of mirrors was never mentioned till 800 years later.

RE: Mythbusters
By mindless1 on 6/26/2008 6:16:57 PM , Rating: 2
Maybe they spent a great deal more time refining it than the basic mythbusters test did. Mythbusters is an interesting show but they try to take a know-it-all attitude instead of realizing they don't actually have all the variables resolved in their one-off tests.

RE: Mythbusters
By tmouse on 6/27/2008 8:21:10 AM , Rating: 2
Possibly but not likely; this is the second or third time they looked into it and the MIT group spent ALOT of time on it. Think about it; a defense like that would not likely disappear. Even though things like the formula for Greek fire are gone there are MANY independent references to it and most of the other colossal weapons developed during that age. There is only a single reference to the magic mirror, the rest are references to it.

RE: Mythbusters
By radializer on 6/24/2008 10:00:11 PM , Rating: 2
If the MIT device is novel, its only because its cheap to build and relatively high efficiency, both of which are very important for the future of solar energy.

Is it truly, though? Not much in the above write-up offers either figures for comparison or relative merits in terms of power concentration efficiency as compared to other existing schemes. I acknowledge the relevance of the MIT team's work but would prefer more numbers and analysis to proclaim that it is "revolutionary" indeed.

The single parabolic dish has the highest energy concentration efficiency - but this does not necessarily translate into gross efficiency since you cannot pack these dishes together as closely as you could a parabolic Trough system or a Fresnel Reflector system.

Also, unlike Troughs or Flat Mirror systems, parabolic dishes need dual-axis tracking (altitude & azimuth or RA and declination; pick your poison) which adds to the complexity of the tracking required. So it would be interesting and more valuable to compare these systems on the gross energy efficiency (energy produced per actual installation area with periphery included) or cost per kWh produced instead.

For reference on parabolic dishes; Sandia Labs has a dish-Sterling system made of laminated aluminum mirrors (82 of them) arranged in the shape of a dish on a steel frame (patented in 1990) that can achieve a net solar-to-electric conversion efficiency that reaches 30%.

For more on Trough and Tower designs, check out this study by the National Renewable Energy Labs

Just for fun, here's a parabolic reflector that they claim could achieve 8500 degrees (not sure what units but still pretty hot) ... check out the page scan from this March 1954 edition of Popular Science

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