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Tuesday, November 13, 2007 Focusing Light on Silicon BeadsPlacing tiny spheres of silicon in reflective trays could be the key to cheap, efficient solar cells. By Duncan Graham-Rowe
A company in Japan has developed a novel way of making solar cells that cuts production costs by as much as 50 percent. The photovoltaic (PV) cells are made up of arrays of thousands of tiny silicon spheres surrounded by hexagonal reflectors. The key advantage of the system is that it reduces the total amount of silicon required, says Mikio Murozono, president of Clean Venture 21 (CV21), based in Kyoto, Japan. "We use one-fifth of the raw silicon material compared with traditional PV cells," he says. This can make a huge difference to the overall cost of producing solar cells, says Howard Branz, principal scientist at the National Renewable Energy Laboratory's National Center for Photovoltaics, in Golden, CO. "About 20 to 30 percent of the cost of a solar-cell module is in the cost of the raw silicon," he says. CV21 started production of its cells in October; the first of its 10-kilowatt modules go on sale this month. While these modules will initially cost about the same as the traditional variety, the price is set to drop by 30 percent in 2008, as production increases in May from 1,000 cells a day to 60,000 cells a day, says Murozono. The ultimate goal is to make them 50 percent cheaper than existing cells by 2010, he says. Spherical solar cells were originally proposed by Texas Instruments about 30 years ago, says Branz. But while they had the potential to reduce the amount of silicon used, they brought with them a host of new problems. Their curved surfaces, for example, can cause more light to be reflected, which reduces their efficiency. What's more, only half of the sphere ends up actually being exposed to light. Significant gaps also tend to form between the spheres when arranged in arrays, which can further reduce the efficiency of the solar cell. CV21's solution was to place each of the one-millimeter-diameter silicon spheres in its own hexagonal aluminium reflector. These work like car headlights but in reverse, ensuring that any light hitting the reflector is directed toward the sphere. When this approach is used, even the underside of the sphere is utilized. The hexagonal shape of the reflectors allows them to be slotted together without dead space between them. "Effectively, these are mini-concentrators," says Branz. The spheres themselves consist of a positively doped (p-type) ball of silicon. The ball's surface is treated to make it negatively doped (n-type), and an antireflective coating is also added. These two outer layers form the basis of the photovoltaic semiconductor material. The spheres are then bonded to an electrode on a flexible foil substrate via a hole at the bottom of the reflector. |
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Tiny Solar Cells
10/18/2007
Comments
cripdyke on 11/13/2007 at 5:06 AM
9
Also, this doesn't seem to be particularly conducive to combining with other techniques that are just now ready to move out of the lab into the market. Some other techs are designed in such a way that they would still benefit from others' advances.
What isn't noted, however, in the text is that the costs here are the costs of manufacture. The tech described, however, is perfectly positioned to save a bundle on installation as well. So...if they can achieve their 50% production cost, and the installation costs are further reduced, the relative ease of manufacture could allow them to build plants in multiple countries and reduce shipping & tariff costs leading to a genuinely competitive product.
So, I give it a 6 out of 10 compared to other techniques that have just left the lab or just hit the market (and the ones in between, such as having finished R&D but the plant isn't up to full production yet).
And what's nice is that it is indigenous to Japan - the other techs that rate higher than this one aren't. With their notable barriers to foreign competition, the Japanese gov't and MITI might be a significant barrier to the economic boost that solar pv will be getting elsewhere in the world ...unless local pv costs fall based on entirely japanese IP/manufacture.
Nice to see that Japan won't (really: might not) be pumping out extra CO2 just because of MITI over the next 8 to 10 years.
ajimenez on 11/13/2007 at 10:56 AM
14
GaryB on 11/13/2007 at 6:23 PM
39
With solar, you have many
Heliovolt, First Solar, Nanosolar etc etc. How are they doing? Where are they at?
cripdyke on 11/15/2007 at 6:46 PM
9
But what I would really like to know is how things are going with combining technology/i.p. from different companies. If they can reach deals on how to share technology so 1 new product can get the benefit of both breakthroughs, prices can drop dramatically.
samlum on 12/02/2007 at 10:13 PM
1
asdar on 11/14/2007 at 9:36 AM
60
Right now CIGS can be produced cheaply, but how about when Galium and Selenium start to feel the crunch.
Silicon shouldn't be that much of a long term problem, but if we're making a true push toward solar we're going to need a hundred times what we're using now, not even mentioning the still blooming computer usage of silicon in China and India.
Demand will most likely continue to rise, and supply might be under a crunch.
Plus, this is technology. Maybe it will lead to something else.
Spothannah on 11/14/2007 at 11:32 AM
1
TimG on 11/14/2007 at 7:42 PM
8
weee on 11/15/2007 at 4:27 AM
31
The news is looking very good indeed - if the cost savings are passed through to consumers; installing solar power will pay for itself in less than 5 years in a sunny climate and 10 years in the UK.
Silacon on 11/15/2007 at 11:18 AM
33
Our company, Silacon, in association with Los Alamos National Laboratory invented a similar array that is useful for PV and blast absorption. Your idea should move to LANL.gov.
anon on 11/16/2007 at 9:55 AM
1
ess on 11/18/2007 at 8:47 PM
1
v-man on 12/11/2007 at 12:46 PM
1
Wow! I guess they ship these 10kw modules on really BIG trucks?