COATING FOR WINDOWS, SOLAR CELLS: A SOLAR BREAKTHROUGH?

Scientists – from theoretical physicists to organic chemists to materials engineers – are daily working miracles of innovation in an effort to find that one disruptive breakthrough that will turn solar energy-generated electricity into an economic proposition. It will happen any day. If the development by Massachusetts Institute of Technology (MIT) researchers of a window coating that increases the efficiency of sunlit window panes (by a factor of 40, according to the researchers) is not it, another technological wonder soon to come along will be.

Nathan Lewis, chemistry professor, California Institute of Technology: "We're not in a hype cycle…There's a lot of innovation we're seeing now, regulations guaranteeing a market expanding for the next decade. . . . If you go to Silicon Valley and around Route 128, everyone and their brother who used to make computer chips are now trying to make thin-film solar cells."

By the middle of the next decade, in most informed observers’ opinions, it will make more sense to use solar energy to make electricity than it will to use coal. At that point, obviously, the game changes.

Allen Barnett, professor of electrical and computer engineering, University of Delaware: "The parallel is microelectronics…Microelectronics started out in big universities, now they are in laptops, cellphones, microelectronic chips all over your home. People think of solar as replacing a coal-fired power plant; it's really different. . . . It is a new way to use electricity and use energy."

Knowing that the change is coming raises a crucial question for every leader and citizen in today’s world: What is the best use of current energy sector dollars?

Is it wiser to build new coal and natural gas plants with unproven greenhouse house gas-capturing equipment or to retrofit existing coal and natural gas plants with the best greenhouse house gas-capturing equipment in anticipation of using them as a bridge to the Age of Sun and Wind and Wave?

Is it wiser to plan to overspend on new nuclear facilities without real solutions for waste storage and disaster safety or to retrofit existing facilities with the best new technology available and use them as a bridge to the Age of Sun and Wind and Wave?

Is it wiser to turn precious, dwindling, hundred-million-year-old supplies of fossil fuels to into liquids for vehicles or to develop renewable, noncrop biofuels from algae and perfect vehicles that plug into a clean grid powered by Sun and Wind and Wave?

There are many ways to answer these questions. There is only one crucial consideration: In the words of Sam Cooke, “It’s been a long time comin’ but a change is gonna come…”

The dyes coated on glass absorb sunlight alter the wavelengths and send it to solar cells at the windows’ edges. Some light passes through to solar cells underneath. (Graphic by Nicolle Rager Fuller, NSF - click to enlarge)

More Efficient Solar Energy Collectors Attach to Windows
Andrea Thompson, July 10, 2008 (LiveScience via Yahoo News)
and
High-Efficiency Organic Solar Concentrators for Photovoltaics
Michael J. Currie, Jonathan K. Mapel, Timothy D. Heidel, Shalom Goffri, Marc A. Baldo, July 11, 2008 (Science)
and
Innovation fuels solar power drive; Rising fuel prices, new technology help make such generation feasible
Carolyn Y. Johnson, July 11, 2008 (Boston Globe)

WHO
Michael J. Currie, Jonathan K. Mapel, Timothy D. Heidel, Shalom Goffri, Marc A. Baldo, research scientists, Massachusetts Institute of Technology (MIT)

WHAT
The MIT scientists have devised a solar energy concentrating window coating that will capture light photons and drive them to photovoltaic devices at the edges of the windows to maximize electricity production.

The abstract of the research report from Science: “The cost of photovoltaic power can be reduced with organic solar concentrators. These are planar waveguides with a thin-film organic coating on the face and inorganic solar cells attached to the edges. Light is absorbed by the coating and reemitted into waveguide modes for collection by the solar cells. We report single- and tandem-waveguide organic solar concentrators with quantum efficiencies exceeding 50% and projected power conversion efficiencies as high as 6.8%. The exploitation of near-field energy transfer, solid-state solvation, and phosphorescence enables 10-fold increases in the power obtained from photovoltaic cells, without the need for solar tracking.”

(Graphic from the Boston Globe - click to enlarge)

WHEN
1979: The Carter administration embraced solar energy research and put solar panels on the White House.
1981: The Reagan administration embraced the fossil fuels industries, took the solar panels off the White House and drastically cut funding for research.
2007: Solar energy generated 0.7% of U.S. electricity.
2011: MIT breakthrough implementation.
2012-13: Algae-based biofuels expected to be produced at commercial scale.
2015: Solar energy expected to be cost competitive with fossil fuel power generation.
2018: Any nuclear power plant begun in 2008 expected to be complete if finished on time without running out of funding.
2025: Solar energy expected to provide 10% of U.S. power generation.
2028: Commercial scale “clean” coal expected to finally be widely available (if still needed or wanted).
2030: Wind energy expected to provide 20% of U.S. power generation.

WHERE
2 or more photon-sensitive dyes are painted on panes of plastic or glass.

WHY
- Research funded by the National Science Foundation and the U.S. Department of Energy's Office of Science.
- The efficiency of the dyes is based on their ability to be layered and capture light at aq variety of wavelengths without interfering with the transparency of the window.
- The theory goes back to research done in the 1970s but the MIT breakthrough was in finding dye concentrations that maximize photon capture and transfer.
- MIT has solar energy research a priority, creating several specific initiatives ex: the $10 million Solar Revolution Project, the Eni-MIT Solar Frontiers Center, the MIT-Fraunhofer Center for Sustainable Energy Systems).

German company Dyesol has been developing a similar concept. (click to enlarge)

QUOTES
- Marc A. Baldo, research team leader, MIT: "[While present sunlight concentrating systems] track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain…Light is collected over a large area [like a window] and gathered, or concentrated, at the edges [in the MIT system]…"
- Jon Mapel, graduate student/team member, MIT: "We made it so the light can travel a much longer distance…We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."
- John Deutch, solar research veteran, MIT: "Tremendous progress has been made, much higher technical performance, for much lower cost…[Today] is not at all comparable to 1979."