Solar cells and the environment impact

Well, once you start looking at the options with solar energy things look pretty rosy right? I mean in ten years from now a third of the produced energy will be solar or otherwise green ( wind power, biomass… ). Most building will be energy self suficient with those fancy dyes on every window and spray-on solar cells everywhere. Right? Well not quite. Everything looks fine until you realize that to produce solar cells NF3 is used. NF3 or nitrogen trifluoride is a gas thats used in the production of LCD displays and solar cells. Unfortunately it is also a very potent green house gas.

Fortunately The Linde Group a world leading producer of gasses has found out that NF3 can be replaced with fluorine gas. Fluorine has no effect on the green house effect and its readily available. On top of that it also speeds the production process thus lowering the costs of solar cells altogether.

For the in detail story click below:

http://www.marketwatch.com/news/story/making-lcd-tv-solar-cell/story.aspx?guid={96198A7A-9B93-43DF-BF35-D7C74148E3F5}&dist=hppr

 

Spray on Solar Cell

One of the breakthroughs in the field came in late 2005 with the invention of a plastic solar cell that can be sprayed on other materials to form a very versatile source of energy. One can envision the material being sprayed on cell phones, laptops, cars … giving the devices true independence from wires and recharging. Larger scale implementations could be the use of the spray to cover entire buildings or even unused land such as deserts to provide an abundant green source of renewable energy.

Scientists are expecting to improve on the efficiency of the plastic cells by harnessing the infrared part of the sun’s light, which represents about 50% of the total light that reaches the earth and which other solar cells cannot use to produce electricity.  Another benefit of this aspect is the possibility to use the cells in cloudy weather or even at night in warm climates as infrared light is actually heat.

With greater efficiency come lower costs. Solar power is infact 3-5 times more expensive than the average U.S. residential power costs. The spray on power cells may finaly brige this gap and bring solar power to the mainstream.

 

The photovoltaic effect

The photovolataic effect is the means by which the photovoltaic cells ( the first generation of solar cell ) are able to transform sunlight into electricity.

A photovoltaic cell is made from a thin slice of semiconductor, usually silicon or galium-arsenide. Two special types of impurities called dopants are added to the semiconductor. The upper and lower part of the slice become respectively a p-type and n-type semiconductor. The n-type has a surplus of electrons while the p-type has a lack of electorns – also called “holes”. This electron imbalance forms an electric field in the semiconductor slice.

When an electron is hit by a photon it becomes free of the p-n structure leaving a “hole” or positive charge behind. Being in an electric field he negative electron and the positive “hole” begin to move in oposite directions creating an electric current. If we connect wires to the semiconductor we can run this current through a load ( light bulb, battery charger, etc ).

Of course not all the photons hit the electrons in the solar cell. Some light bounces right off the cell and some misses the electrons and passes right through. Also the semiconductors used today are able to absorb just about half the spectrum of sunlight, further limiting the efficiency of cells.

The efficiency of photovoltaic cells can be raised using different combinations of semiconductors to try to absorb the whole length of the sun’s specturm and also use thicker slices with more p-n junctions to catch the photons that pass thorough the first junction.

 

Solar power technology

Many of us might thing that solar cells are something new and cutting edge. Well the truth is that they have been around for decades. The buzz surrounding them now is caused mainly by the soaring gas prices and the green movement in general. The solar cells technology is at its third generation.

The first generation the classic photovoltaic silicon based cells still represents more than 80% of all the installations. They are highly effective but bulky and expensive.

The second generation tries to address the shortcomings of its predecessors. The lightweight and flexible thin-film solar cells are very low cost. They can be arranged in many different ways making their use much more suitable for urban settings. Despite their lower efficiency they are expected to dominate the solar market in a few years.

The third generation of cells are actually a group of technologies that are still being researched. The research is directed towards new materials like polymers and nanotechnology and away from silicon-based materials. The idea is to merge the flexibility and low cost of the thin-film cells and the effectiveness of the classic silicon based cells. I will try to cover the new technologies in a later post.