The old saw that “the devil is in the details” characterizes the kind of needling obstacles that prevent an innovative concept from becoming a working technology. It also often describes the type of problems that must be overcome to shave cost from the resulting product so that people will buy it.
Emanuel Sachs of the Massachusetts Institute of Technology has struggled with many such little devils in his career-long endeavor to develop low-cost, high-efficiency solar cells. In his latest effort, Sachs has found incremental ways to boost the amount of electricity that common photovoltaics (PVs) generate from sunlight without increasing the costs. Specifically, he has raised the conversion efficiency of test cells made from multicrystalline silicon from the typical 15.5 percent to nearly 20 percent—on par with pricier single-crystal silicon cells. Such improvements could bring the cost of PV power down from the current $1.90 to $2.10 per watt to $1.65 per watt. With additional tweaks, Sachs anticipates creating within four years solar cells that can produce juice at a dollar per watt, a feat that would make electricity from the sun competitive with that from coal-burning power plants.
Most PV cells, such as those on home rooftops, rely on silicon to convert sunlight into electric current. Metal interconnects then funnel the electricity out from the silicon to power devices or to feed an electrical grid.
Since solar cells became practical and affordable three decades ago, engineers have mostly favored using single-crystal silicon as the active material, says Michael Rogol, managing director of Germany-based Photon Consulting. Wafers of the substance are typically sawed from an ingot consisting of one large crystal that has been pulled like taffy out of a vat of molten silicon. Especially at first, the high-purity ingots were left over from integrated-circuit manufacture, but later the process was used to make PV cells themselves, Rogol recounts. Although single-crystal cells offer high conversion efficiencies, they are expensive to make. The alternatives—multicrystalline silicon cells, which factories fabricate from lower-purity, cast ingots composed of many smaller crystals—are cheaper to make, but unfortunately they are less efficient than single-crystal cells.
Sachs, who has pioneered several novel ways to make silicon solar cells less costly and more effective, recently turned his focus to the details of multicrystalline silicon cell manufacture. The first small improvement concerns “the little silver fingers that gather electric current from the surface of the bulk silicon,” he explains. In conventional fabrication processes, cell manufacturers use screen-printing techniques (“like high-accuracy silk-screening of T-shirts,” Sachs notes) and inks containing silver particles to create these bus wires. The trouble is that standard silver wires come out wide and short, about 120 by 10 microns, and include many nonconductive voids. As a result, they block considerable sunlight and do not carry as much current as they should.
At his start-up company—Lexington, Mass.–based 1366 Technologies (the number refers to the flux of sunlight that strikes the earth’s outer atmosphere: 1,366 watts per square meter)—Sachs is employing “a proprietary wet process that can produce thinner and taller” wires that are 20 by 20 microns. The slimmer bus wires use less costly silver and can be placed closer together so they can draw more current from the neighboring active material, through which free electrons can travel only so far. At the same time, the wires block less incoming light than their standard counterparts.
The second innovation alters the wide, flat interconnect wires that collect current from the silver bus wires and electrically link adjacent cells. Interconnect wires at the top can shade as much as 5 percent of the area of a cell. “We place textured mirror surfaces on the faces of these rolled wires. These little mirrors reflect incoming light at a lower angle—around 30 degrees—so that when the reflected rays hit the glass layer at the top, they stay within the silicon wafer by way of total internal reflection,” Sachs explains. (Divers and snorkelers commonly see this optical effect when they view water surfaces from below.) The longer that light remains inside, the more chance it has to be absorbed and transformed into electricity.
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Add CommentWhat about the cells made into panels that ordinary roofers can install?
Reply | Report Abuse | Link to thisPhogat, it depends what question your asking. I think, (though I was listening to raining blood throughout reading this article) that the difference between the two is the 120 by 10 microns one has many gaps, and glass if going to be added to allow the light to essentially be trapped.
Reply | Report Abuse | Link to thisIn short, ordinary roofers should be able to install this anyway... there doesn't seem to be that much change, maybe in the wires. If anyone knows...?
JUST AN IDEA ABOUT SOLAR
Reply | Report Abuse | Link to thisAS A HOME OWNER I DRED REPLACING MY ROOF BECAUSE OF THE COST. MY HOME IS 85 YEARS OLD IN THE INNER CITY.
i KEEP HOPING SOMEONE WILL COME UP UP WITH AN IDEA TO KEEP INSTALLATION COSTS DOWN. EVERYONE KEEPS HOPING THAT NEW TECHNOLOGY WILL INCREASE $ per watt RATIOS OT OVERCOME INSTALLATION COSTS
MY LATEST THOUGHT IS A FLEXABLE BASE TO PUT THE CELLS ON.
LIKE A HUGE SHEET OF SEMI-FLEXABLE UV RESITENT PLASTIC
THAT CAN SIMPLY BE PULLED OVER THE ROOF AND THEN SECURED FROM WIND PROBLEMS.
IF IT COULD LAST 5 YEARS AND THEN HAVE THE VOLTAIC PROPERTIES RECYCLED THEN WERE IN A RENEWABLE ERA WITH THAT TOO.
IT JUST MAKES SENSE TO START DEVELOPING
SOLAR ENABLED ROOFTOPS FOR OLDER HOMES.
MY THOUGHT IS APPLY IT OVER AN EXISTING ROOF TOP
BUT APPLY IT LIKE A STIFF 8 FOOT WIDE WALL PAPER - SEMI FLEXIBLE
THAT ADDS AN ADDITIONAL LAYER WATER PROOFING TO THE ROOF.
SO THATS IT MY IDEA IS
RECYCLABLE SOLAR WALLPAPER THAT CAN BE PUT ANYWHERE.
ON ROOF TOPS
OVER LAWNS
ON TOP OF CARS
ALONG HIGHWAYS
BUILDINGS
STADIUMS
SIDE WALKS
WIND TURBINE POLES AND BLADES
BLIMPS ,BOATS . RAILROAD CARS - RAILROAD TRACKS ,TRACTOR TRAILERS
SEASONAL ROLLOUTS
AS A WINTER FARM CROP
PARKING LOTS , FENCES
MOUNTAINS
PLANETS , WORLDS, AND ORBITS
OK THAT MAY BEING GOING TO FAR BUTT.
i REALLY THINK HOME OWNERS WOULD FLOCK TO IT AND THUS PROVIDE MUCH OF THE MONEY NEEDED TO DRIVE NEW INNOVATIONS.
I KNOW THIS CONCEPT COULD SPIN WILDLY OUT OF CONTROL .
IN MY OPINION THINGS ARE ALREADY OUT OF CONTOL WITH CLIMATE CHANGE POSSIBLY BEING MASKED BY SOLAR DIMMING. COVERING LARGE AREAS OF EARTH WITH RECYCLABLE BLACK OR WHITE WALLPAPER SEEMS TOO COSTLY
UNLESS THE PAPER IS ACTUALLY PROFITABLE
AND A ECO FRIENDLY POWER SOURCE. THAT CAN REMAIN AFTER GREENHOUSE CRISISES ARE LONG GONE.
SAMUEL_MARCHBANKS
Reply | Report Abuse | Link to thisHi, Could some one please tell me how or where to find out about making Amorpohous solar panels. What inks are used and what order they are put on and how do you connect the leads off it. I think there is huge potential in creating light wieght plastic solar panels like they make for backpacks to cellphones etc.
Reply | Report Abuse | Link to thisWhat if plastic concentrators are placed over the solar panels to substantially increse the input sunlight? Would higher temperature then decrease the efficency of the solar panel?
Reply | Report Abuse | Link to thisWhy cant one put plastic lenses over the sols panel to increase the solar input? Would the higher flux decrease the efficiency of the solar panel?
Reply | Report Abuse | Link to thisPlay in the Day! I have seen ball fields with lights on day and night. Games were once played during the day. Let's do it again.
Reply | Report Abuse | Link to thisIf you can't watch it in the day, have local news channel film and show you at 8. Sure would cut out the need for many coal fired plants.
Play in the Day!
Reply | Report Abuse | Link to thisGet local schools involved, collecting alluminum, etc. Teach how to make solar cells in schools.
There is atleast one building in everytown that cold be making solar cells. If this is going to cut someone's electric bill and clean the environment for their children. They will participate......
can we plan to raise and lower the panels so that it will match the sun's angle?
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Thanks for the post. What is the concentration of <a href="http://budcare.com">organic hydroponic nutrients</a> in these silicon solar cells? This could seriously affect the performance.
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