October 17, 2006 4:31 PM PDT

Sharp expanding beyond silicon in solar

SAN JOSE, Calif.--Sharp Electronics, one of the largest manufacturers of silicon solar panels, is experimenting with new materials.

At the Solar Power 2006 Conference and Expo here, the company is showing off several prototype solar panels and a new system it hopes will increase efficiency and make it easier to install new solar systems. One prototype solar panel combines a tiny solar cell measuring about a quarter of an inch per side that sits beneath a Fresnel lens (a ridged lens originally used in lighthouses), which radically concentrates sunlight. Further improving its performance, the solar panel rotates with the sun.

Overall, Sharp says the panel can convert 36 percent of the sunlight that strikes it into electricity, far higher than the 13 to 22 percent conversion rates of commercial silicon solar cells.

Solar Power 2006

Sharp has also developed prototype solar cells that combine a layer of amorphous silicon and a layer of conventional, crystalline silicon, said Ron Kenedi, vice president of Sharp's solar-energy solutions group. These solar cells are nearly transparent, so they could potentially be used in windows. Sharp has installed some of these cells at its latest LCD (liquid crystal display) plant in Kameyama, Japan, which obtains much of its power through various "clean" energy sources.

In another experiment, the company has inserted a layer of LED (light-emitting diode) lights between the two layers of the experimental combo cells. The solar cells power the LED lights, which can then light a room at night. Sharp is also experimenting with solar cells made from organic materials and different types of silicon.

The experimentation arises from a belief that different types of panels will be required for different applications, said Kenedi.

"You can't use the same product on the ground as on the roof. You have to have different weapons for each one of the wars," he said.

Cheap and easy
The solar panel with the concentrating lens is one example of a use-specific panel. This system, which may come to market in the next year or two, would be used for solar power plants--large installations in a field that would pass power onto the grid. These systems, for example, most likely would not be seen on suburban rooftops.

The underlying solar cell, which converts sunlight to electricity, in these panels is made out of III-V compounds (molecules made from elements in the III and V columns of the Periodic Table of Elements). Producing chips from these materials, such as gallium arsenide, is expensive. Thus, the solar cell needs to be small. The lens, by contrast, is much less expensive and measures a few inches across. The panel itself measures about 12.5 feet by 16 feet and contains 270 lenses. Overall, a complete panel with 270 lenses can churn out 2.9 kilowatts and rotates with the sun for maximum efficiency.

Unlike traditional solar panels, these panels require direct sunlight and can't, for example, harvest energy from light reflected off snow. So they work best in dry areas with lots of sunlight, such as the southwestern United States.

"The cell is expensive if you use it as it is," without the lens, acknowledged Kenedi, "but it will outperform traditional solar cells in the right conditions." The lens concentrates the energy to make it seem as if 700 suns are pointing at the solar cell, he added.

Sharp is also producing equipment for conventional silicon solar panels. At the show, the company announced that it hopes to bring what it calls a solar racking system to the U.S. The system, which is already in use in Japan, essentially cuts down the time it takes to put a solar system on a roof by about 20 percent.

On the consumer front, Sharp announced a partnership with Citibank that will let customers finance new solar systems through a home equity line of credit.

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10 comments

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Solar on cars
Pretty soon I will just be able to snap my fingers for all my energy consumption needs, and then... it will still cost money. Someone will charge me for snapping my fingers

If they do get solar to except more energY mnaybe solor powered cars will become more viable.
Posted by Blito (436 comments )
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Who knows, but probably not
If you are interested in solar cars, they do hold a race once a year that goes cross country using solar powered cars. They are purely experimental, expensive, and not designed for general purpose use. I beleive the winner went about 40 mph average.

Perhaps one day you will see an electric car that suppliments its charge with solar, but will also plug into a wall outlet for charging. A pure solar car doesn't have the energy capacity to maintain what we expect in automobile performance.
Posted by Seaspray0 (9714 comments )
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It is needed
I really expected embedded solarcells (or solarpaint) to have been there already. Enough to cool a car interior, trickle charge batteries and any owner devices within.
Instead, we have automakers more concerned with price-gouging the green buyer, and focused on "bling" rims a lowprofile tires...on SUVs and Trucks! No wonder the Japanese should get a pat on the back for their determination at providing a solution.
Posted by Below Meigh (249 comments )
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Numbers don't seem to add up
Supposedly the lensed solar arrays are 36% efficient.

Supposedly a 12.5 foot by 16 foot (approximately 18.6 square meters) outputs 2.9 kW.

The solar constant (the amount of light hitting the Earth) is over 1.35 kW per square meter. Even assuming 50% of that is lost in the atmosphere (which it's not, but I'm too lazy at the moment to look up the actual percentage) this would be over 675 watts per square meter. Thus a minimum of 12.5 kW falls on that 18.6 square meter array.

With only 2.9 kW out (in the form of electricity) and over 12.5 kW in (in the form of light) This gives an average efficiency of about 23% -- no where near the claimed 36%.
Posted by shadowself (202 comments )
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Numbers don't add up
I think alot of the panel space is taken up by the lens and the actual solar panel area coverage is much less.
Posted by (14 comments )
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Numbers may add up
Well, the article is not well written so there is this uncertainty about the numbers, but the 2.9 kW could add up.

It is 1 kWp/m^2 on the Earth's surface, so:
1 kWp/m^2 * 18.6 m^2 * 36% = 6.7 kWp can be converted at direct normal sun. Their number of 2.9 kW is 43% of 6.7, so there are two options:

1. They are being conservative and adding losses for inverter, performance ratio, actual cell efficiency due to not be a lab-based cell and temperature differences (possibly the 36% efficiency is only for non mass-produced cells). However, 43% is a large loss.

2. They are not talking about peak wattage but rather average wattage over the course of the solar irradiation cycle (for instance, 24 hours). For a flat-panel non-tracking PV panel, the irradiation gets about an equivalent of 5 hours per day of full peak sun (1 kW/m^2). For a tracking panel, this could maybe be 10 hours I am guessing, which is about 42%. So they are then quoting a maximum power output averaged over the course of a day, with optimum tracking and optimum cell efficiency.

I think #2 is most likely.
Posted by Hardrada (359 comments )
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microconcentrator cells
What has to be kept in mind about microconcentrators is that they magnify the sunlight hitting so instead of one sun your getting 100x suns thereby increasing the effective efficiency. In concentrators you are trading off high cost PV semiconductor real estate for lower cost concentrator so on a $/W basis you are ahead. For an American microconcentrator design see SunPower's ATP project at <a class="jive-link-external" href="http://jazz.nist.gov/atpcf/prjbriefs/prjbrief.cfm?ProjectNumber=99-01-4040" target="_newWindow">http://jazz.nist.gov/atpcf/prjbriefs/prjbrief.cfm?ProjectNumber=99-01-4040</a>
Posted by pzev (20 comments )
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solar PV on cars
Back in the 1990s a number of thin film PV companies (notably ARCO Solar)developed thin film a-Si sunroofs to power a fan to keep car temperatures down during the summer. This application never attracted enough interest from customers. Remember that to power a car you need 60-100 kWatts of power. A 4 sg ft solar panel provides 100-200 watts so even stored in a battery solar PV doesn't provide enough energy to make a significant contribution to battery recharging.
Posted by pzev (20 comments )
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