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Future of Solar Power: How About
Transparent Solar Cells That Can Be Put On Windows?

Hari Pulakkat
Economic Times, August 5, 2013

When you scour the world of solar energy research for potential game-changing advances, most people would focus on a few areas: high-efficiency solar cells, transparent solar cells, hydrogen through solar water-splitting, or solar thermal.

Last week saw breakthroughs in the first three of these fields, and three weeks ago there was another breakthrough in solar thermal.

There is a strong possibility that at least some of this research will result in successful commercial technologies in a few years, expanding the possibilities of solar energy and making it work without subsidies.

Solar energy, as we use it now, consists largely of photovoltaic installations; those that use light from the sun to generate electricity. The problem with photovoltaic solar is its low efficiency. Current solar cells absorb only part of the visible spectrum of light, and a solar panel can face the sun only during part of the day.

Of course, you can design more complicated cells that absorb more light, or add sophisticated machinery to track the sun's movement throughout the day. Suntracking can be especially useful at times, and can increase the efficiency substantially in some cases.

But these additions also increase the cost, and in the end are not as useful as they first seem. Which is why even some of the most optimistic long-term projections for solar energy fall short of what the earth needs. Greenpeace, for example, estimated that solar energy can serve 9% of the world needs by 2030 and 20% by 2050. Considering that by 2050 the world needs to reduce carbon dioxide emissions by 80%, solar energy needs to contribute far more than 20%.

This cannot be achieved without paradigm shifts in technology. And the current scenario looks extremely promising. Consider a recent paper in the journal Applied Physics from Lawrence Livermore National Laboratory, a top-notch research institute near Silicon Valley. It has made a cell with 95% efficiency by using the entire range of sunlight colours that make the rainbow, and then adding infrared at the top and ultraviolet at the bottom.

Their scientists use a plasmonic solar cell, a promising third-generation technology that uses the bizarre laws of quantum mechanics to achieve high efficiency at low cost. The second-generation thin film cells are not able to break through commercially because of their poor efficiency.

Many think that plasmonic thin films can break this barrier and make the technology applicable on a large scale.

Splitting Water

The other breakthroughs are a transparent solar cell from the University of California in Los Angeles, a simple solar cell from Germany that can split water and produce hydrogen, and a photovoltaic-thermal system from Canada. Transparent solar cells are an exciting development as they can be put on windows, gadgets and in other places to generate electricity on the sly.

Producing hydrogen from water using sunlight is a dream of the solar energy world, as it lets us store the energy -- in the form of hydrogen gas or in a fuel cell -- that can be used at night or on cloudy days. Combining photovoltaics with thermal uses both light and heat from the sun.

There is a long way from a technology demonstrator in the lab to a commercially successful device. In the field of solar energy, this is important, as the cost of commercialisation can at times be very high. We do not know how these technologies will end up, but there is no need to belabour this point. Lab-scale technologies are developing at high speeds, and it may be only a matter of time before a game changer arrives.

Hari Pulakkat
Future of Solar Power: How About Transparent Solar Cells That Can Be Put On Windows?
Economic Times, August 5, 2013

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