Nanotech: The Next Big Thing in Solar

Nanoantenna, courtesy of  Idaho National Lab

Imagine this, a photovoltaic (PV) panel as thin as a piece of foiland produced by printing it like a newspaper. Now imagine using a sprayto convert your window into a transparent solar panel. It’s all happening now as companies and researchers adoptnanotechnology production methods to the world of PV. This new class ofphotovoltaics, called nanophotovoltaics, are starting to enter themarket in 2010. As the technology continues to advance, it may helpspeed the adoption of PV.

Nanophotovoltaics are the third generation of PV and the latest inthe quest to develop less-expensive solar panels that are cheaper toproduce, and lighter than their predecessors. Right now scientists arecreating photovoltaic panels using technologies including carbonnanotubes, multiple quantum wells, nanowires, nanoantennas, and quantumdots. These nanophotovoltaics can consist of PV components that are1/1,000th the thickness of a human hair, and are printed directly ontosheets of metal or other substrate.

By using these mighty micro PV conductors, companies are greatlyreducing the amount of materials needed to make a PV cell, and are ableto cut production costs. While some are market-ready and are already ontheir way to PV installations, other technologies are still beingresearched to determine their efficiency and how inexpensive they are to produce.

Nanoparticle ink panels

Nanosolar is one company that’s now making partnerships to market its panels, which consist of a nanoparticle ink printed on a thin foil. You can see a video of the printing process here. The National RenewableEnergy Laboratory (NREL) certified that the PV foil is capable ofcapturing 15.3 percent of the sun’s energy. That puts the technology inthe range of most photovoltaics including thin-film and silicon. At this point, most installed systems convert between 10 to 11 percent of thesun’s energy into electricity, NREL said. However, commerciallyavailable photovoltaics convert between 8 percent and 20 percent ofsunlight into energy.

Nanosolar has had two plants making photovoltaic panels. The first is in San Jose, CA, and a newer plant is in Germany. The company’slong-term goal, when the production process is fully optimized, is toproduce photovoltaic panels at 60 cents per watt and retail them forabout $1.00 a watt, according to company spokesperson Joey Marquart.When that efficiency is reached, a fully installed Nanosolar panelsystem would cost about $2.50 a watt.

Nanosolar is field-testing its solar panels now and plans to increase deployment of the panels “sevenfold” in 2010, Marquart said.

Thinner still, Nanowires are on the Horizon

Another promising PV technology being developed at the LawrenceBerkeley National Laboratory is silicon nanowires, which are about1/1,000th the thickness of a human hair. Each nanowire is a completephotovoltaic cell with a p (positive) and n (negative) junction,according to the lab. By incorporating a p-n junction into each wire, it greatly reduces the distance of electric transmission to electrodes and allows electricity produced by the wire to move much faster across thepanel’s surface.

Cells manufactured with nanowire technology use minute amounts ofsilicon and can use lower-grade silicon, making production much lessexpensive than crystalline silicon cells, which need expensive,high-grade silicon. The lab said that with improvements, PV panels madewith nanowire technology should be suitable for large-scale deployment.

At this point, panels made of nanowires are 5 percent to 6 percentefficient at converting sunlight to electricity. However, chemistPeidong Yang, who led the research, asserted that this efficiency wasreached with little effort in efficiency-increasing modifications.

“With further improvements, most importantly in surface passivation,we think it is possible to push the efficiency to above 10 percent,” heexplained. “The fabrication technique behind this extraordinarylight-trapping enhancement is a relatively simple and scalable aqueouschemistry process.”

He added, “We believe our approach represents an economically viablepath toward high-efficiency, low-cost thin-film solar cells.”

Microscopic antennas: 80 percent efficient and produce PVpower after dark

Some PV nanotechnology promises to be the most efficient PVtechnology yet. Nanoantenna arrays have captured up to 80 percent of the sun’s rays mid-infrared rays at the U.S. Department of Energy’s IdahoNational Laboratory. The nanoantennas are 1/25th the width of a humanhair.

The lab said the material, which looks like gold on a sheet ofplastic, could “cost pennies a yard, be imprinted on flexible materials, and still draw energy after the sun has set.” Yeah, photovoltaic powerproduced after dark. These tiny antennas are able to produce energy from infrared light reradiated from the earth after dark. They also are able to absorb infrared heat from other things, like industrial processes.And researchers think the material could produce electricity from wasteheat, allowing the nanoantennas to cool buildings and computers withoutair conditioning.

There’s just one teensy problem. The electricity produced by thenanoantennas moves too fast. The alternating-current (AC) electricitythey produce oscillates trillions of times every second. To compare, the AC power used throughout the U.S. oscillates at 60 times a second.Electric lines, transformers, as well as appliances and motors poweredby conventional AC electricity can’t handle the higher oscillations.

"We need to design nanorectifiers that go with our nanoantennas,"researcher Dale Kotter explained. A nanoscale rectifier will require new manufacturing methods since it is about 1,000 times smaller thanavailable commercial rectifiers. Another possibility is developingelectrical circuitry to slow the current to usable frequencies.

Originally etched into a gold silicon wafer, researchers at the labhave achieved the same efficiency results by depositing the antennas on a plastic, like those used for food-storage bags.

The lab partnered with Microcontinuum Inc. and Patrick Pinhero of the University of Missouri, to develop the material.

Nanospray? Is that like sunscreen?

Not quite. New Energy Technologies, Inc. said it developed a methodof spraying windows with a transparent nano-thin PV material. Its PVcells are 1/4 the size of a grain of rice and 1/1,000th the thickness of a human hair. The tiny cells produce electricity both from natural andartificial light. The techonology was developed by the company inpartnership with the Nanostructure Optoelectronics Lab in USF.

The company is developing a product called SolarWindows, which willuse the spray process to create electricity-producing windows. However,the company did not disclose how efficient the PV windows are.

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Invisible PV Windows Will Soon Power Your Lights

Ultra small solar cell, courtesy of New Energy Technologies

Building-integrated photovoltaics (PVs) are undergoing arevolution, from thin, visible PV wafers suspended in window panes tofully integrated into the windows themselves. Thanks to nanotechnology and advances in photovoltaic materials, some PV cells are now thinnerthan a strand of hair, and no bigger than a quarter of a grain of rice.And by replacing metals with certain hydrocarbon-based plastics, theycan be made virtually invisible. This makes them ideal for a variety ofapplications, like turning windows into PV devices that can help power or offset abuilding’s energy use.

New Energy Technologies has developed a spray-on application thatconverts a window’s surface into a PV unit. The spray-on PV cells areapplicable at room temperature and in normal conditions. The companysaid its SolarWindow units will be able to absorb light energy not onlyfrom the sun, but also from artificial light, like that produced bylights inside the office. The company was able to eliminate all metalfrom the cells, making them more transparent and easier to apply. NewEnergy is currently developing the production process to scale it up for commercial production.

Other companies are nipping at its heels. Peer Plus, a company in the Netherlands, unveiled its Smart Energy Glass, which produceselectricity that powers its electrochromatic abilities—ability to shadewhen small amounts of electricity are applied—and also provides PVgenerating capabilities for use in a building. The company said it haspilot projects underway in the Netherlands, but offered no otherinformation about its projects. In its bright mode it allows allsunlight in; in its privacy mode, the window turns opaque; and in itsdark mode, it allows for additional shading.

Konarka, a producer of organic PV, made an agreement in 2009 withArch Aluminum & Glass to integrate Konarka’s Power Plastic PV filmin its windows. In November 2009, they introduced a 1.5 kilowatt PVpilot project at Arch’s office building in Tamarac, Fla.

A technology being developed at MIT uses layers of glass, each dyed a different color to collect different spectrums of sunlight at theglass’ edge. At the edge, small efficient PV cells collect the energyfrom each pane. The focused solar radiation increases the electricalpower generated by each solar cell "by a factor of over 40," said MarcBaldo, MIT Associate Professor of Electrical Engineering.

As these new technologies make it to market, they’re likely to firstfind commercial applications, like windows in office buildings andhigh-rises. But, hopefully, homeowners can one day replace their windows with more efficient, active PVwindows.

-Chris Meehan

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