Solar dish scales down - project of MIT students

Sustainable Futures - from environmentalresearchweb - Aug 14, 2008

Solar dish scales down

A group of students at the Massachusetts Institute of Technology (MIT), US, has developed a small, easy to make, cost-efficient solar dish that might be mass produced by the company they have set up, RawSolar.

The dish consists of a 12-foot wide, mirrored parabola that concentrates sunlight by a factor of 1000. Attached to the dish's centre is a coil of copper tubing 12 foot long that has water running through it. When the dish is pointing directly towards the sun, the water in the coil instantaneously heats up to form steam. This is because the sun's rays converge onto the copper coil, providing intense energy. The steam comes out of the far end of the tube under the dish.

Led by Spencer Ahrens, the students hope that RawSolar will one day mass produce the dishes. They could be set up in large arrays to provide steam for heating, industrial processes, generating electricity, or even air conditioning.

The beauty of the new dish lies in its size – it is smaller than conventional dishes and so requires less support structure, which means it costs less, too. It is also robust (it has already survived a thunderstorm), uses easily-available, off-the-shelf parts and was made by hand, explains team member Matt Ritter.

The structure was based on a design by Doug Wood, an inventor based in Washington state. Wood patented key parts of his design – the rights to which he has now signed over to the MIT students – and says that Ahrens' team has made significant improvements to the original patterns. "They really have simplified this and made it user-friendly so that anyone can build it," he explained.

The students made their solar dish by riveting aluminium tubing to a steel crossbracing. Strips of mirror were then fixed to this frame and the coil collector at the top of the tube painted black.
The MIT team says the system could produce heat from steam for lower costs than that from oil or natural gas.

"I've looked for years at a variety of solar approaches, and this is the cheapest I've seen," said MIT Sloan School of Management lecturer David Pelly, in whose class this project first took shape last autumn. "And the key thing in scaling it globally is that all of the materials are inexpensive and accessible anywhere in the world." Pelly adds that the technology could scale without subsidies – a first in the solar dish world.

Cells lead astray

The New York Times has an article in today's Science section about lead, and its historical uses. It's not hard to see why people were so enthusiastic about lead in ancient times-- it's easy to find and recover, it has a low melting point, and it's malleable. Lead also gets cozy with sulfur, which is why there are so many health problems associated with it. Some of these problems were known by Hippocrates in 400 BC, but lead was so useful that people weren't ready to do without it. The most significant problems are experienced by young children, whose brain development is affected by lead molecules which disrupt some proteins by seeking out sulfur. Other animals are also affected by ingesting lead.
In my previous career in public health, I became a Certified Lead Inspector for housing. In New England, with its older housing stock, lead paint is a persistent issue. While Europe banned the residential use of lead paint in the 1920s, the US didn't until the Consumer Product Safety Commission issued a regulation in 1978 prohibiting its use in residential settings. At first, I thought that flaking lead paint was the big problem, since kids often eat the flakes (Apparently, lead lends a sweet taste to substances, which is why the Romans used it to treat wine.), but it is also present in house dust as a result of friction on window sashes and door jambs. Lead from gasoline contributed to the environmental load as well.
Here are some UMass Library databases you can search for more information on lead in the environment and it's effects on humans and other animals. Remember that you may have to use your OIT login information if you want to connect from off-campus.
CAB Abstracts
Engineering Village
Environment Index
Food Science and Technology Abstracts
Kirk Othmer Encyclopedia of Chemical Technology
LexisNexis Environmental
PubMed: UMass Amherst subscription
Web of Science
Zoological Record
If you're interested in the biochemistry of lead, try Beilstein.