Net Zero or Net Gain? Next Generation Solar:

In this article we explore the use of Transparent Solar Glass to create electricity while providing lighting in architecture on
a mass scale, and more so, to do it in an environmentally sustainable fashion.

Can cities of the future give back to an aging power grid?
Will new solar technologies be the key to self-sustaining architecture?

The world is grappling with the question of how to provide for growing energy needs in the foreseeable future. With projected electricity usage worldwide increasing 60% to 70% by the year 2030 (DOE 2008 energy projections), the current energy infrastructure is operating beyond its carrying capacity in most developed regions. Civilization is in need of innovative solutions to help meet the energy needs of the future. The race is on to develop and implement new technologies capable of providing affordable, clean, and renewable energy for the world of tomorrow.
The question of how to provide for growing energy needs is pressing. There is no clear strategy to address the expanding need for electricity in today’s aging infrastructure. The current methods of energy production are ecologically and economically maladapted with energy costs continuing to rise. It is critical that sustainable energy solutions be developed to meet growing energy needs while minimizing the impact on the environment. Recent breakthroughs in solar technology may provide the chance to rethink how the energy of the future is produced and to help overcome the limitations that have been preventing solar use from evolving into a viable means for wide-scale use in cities. A net-zero pollution index has become achievable.
One of the most prominent issues facing civilization is growing need for energy and its production (or lack thereof). Aging energy infrastructures are beginning to feel more strain as power users in modern cities increase in number. Power companies are struggling with the impact of growing demand while having few plans for increasing production on the scale needed to meet projected demand. Even the increase in computer servers used by businesses is putting a noticeable strain on the power system. The prospect of new electric cars on the road will reduce emissions in the city, but how will that balance out with the extra fuel being burnt in coal-fired electrical power plants? Clean energy solutions from alternative green energy sources have been elusive on a large scale and a drastic turnabout is needed in order to avoid devastating consequences to our ecosystem. It has become a runaway train, consuming increasing amounts of resources to meet the growing demands of our population.

The Answer May Seem Obvious to Solar Enthusiasts Everywhere
It is well known that the amount of energy received from the sun could power the planet beyond imagination. Electricity from the sun is an abundant and free source of energy. Why then are the sun’s rays not being harnessed and converted into electricity on a broader and more massive scale? Solar power amounts to less than one percent of the total energy consumed in the US and throughout the world. Yet the Earth receives 1000 watts of power per square meter from the sun during daylight time excluding cloud cover. The amount of energy from the sun that the earth absorbs is known as irradiance. Irradiance is the measure of the sun’s power available at the surface of earth. The average solar cell in use today is known to operate at around 16% efficiency and currently 130 watts per meter of silicon can be converted. If solar could be incorporated into urban and architectural design and commercial applications, then perhaps entire city centers could be brought to a status of net zero energy usage.

Solar Energy: How Is It Produced and What Are Its Limitations?
Currently solar power is produced in many ways. One common method is the solar concentrator, which is used to concentrate sunlight using mobile mirrors that track the sun as it travels across the sky; the light is focused onto a small high-performance silicon photovoltaic panel similar to traditional flat panel solar cells. One drawback to this method is that the intense heat created from the concentrated rays reduces the efficiency of the panels.
Another choice is the Concentrated Solar Thermal (CST). The CST concentrates the sun’s rays to create heat and – indirectly – electricity (through steam spinning a turbine and the turbine spinning a generator similar to the one in a car). There may be a way to increase electrical output with the CST by reusing the waste heat in a thermoelectric process before releasing the steam into the air.
What we are most likely to see in everyday life, though, is a traditional silicon photovoltaic cell (PV). These are the fixed panels that are placed on the roofs of buildings and houses and do not need to track the sun. Light reaching the panels is absorbed and converted to electricity through a semi-conducting process. PV-embedded glass is beginning to be used architecturally.
Why are non-renewable resources like coal and natural gas still being used when solar technology has been around for decades? The main reason is that silicon cells used to convert the sun’s rays into electricity have been prohibitively expensive to manufacture on a large scale. One other aspect of traditional silicon photovoltaic cell is that the industry that creates them releases significant amount of nitrogen trifluoride. Nitrogen trifluoride is a colorless, toxic, flammable gas that is 17,000 times more effective as a green house gas than an equal mass of carbon dioxide. Nitrogen trifluoride is used to etch silicon wafers for microelectronics.

Researched and written by
Kevin Meaney

Photography by
Donna Coveney

Image courtesy
Nicolle Rager Fuller, NSF

Covalent Solar
An example of a dye-sensitized solar cell array - provided by Dr. John Bell.
Collecting light across their entire surface and concentrating it at the edge allows luminescent solar collectors to reduce the required area of the solar cell and, consequently, the cost of solar power. Layering and stacking multiple concentrators allows the LSC solar cells to collect energy
at specific wavelengths, increasing the
power output.
An artist’s representation shows how a cost-effective solar concentrator could help make existing solar panels more efficient. The dye-based organic solar concentrator functions without the use of tracking or cooling systems, greatly reducing the overall cost compared to other concentrator technologies. Dye molecules coated on glass absorb sunlight, and re-emit it at a different wave-lengths. The light is trapped and transported within the glass until it is captured by solar cells at the edge. Some light passes through the concentrator and can be absorbed by lower voltage solar cells underneath. Alternatively, the partially transmissive concentrator can function as a window. Graphic not to scale. Image courtesy / NSF
MIT Associate Professor Marc Baldo (left), and Shalom Goffri (right), Postdoctoral Fellow in MIT’s Research Laboratory of Electronics, holding an organic solar concentrator.
Transparent Gratzel Cells manufactured by Dyesol allow rosy colored light to pass through while deflecting heat, thereby offering means to reduce cooling cost in warm climates.

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