IS THERE A COAL BASED SOLAR CELL IN OUR FUTURE?
by Harold Hough

Coal and solar cells may have more in common in the future than you think.  In recent months there has been a burst of interest in Polymer Solar Cells thanks to research showing them able to reach efficiencies of over 10%.  And, since this is a Coal Bin article, that means they are partially made from coal.
Before going into greater detail, here’s a simple explanation of how a solar cell works.  Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon. 

Then the electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.  An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.

Traditionally silicon has been used for solar cells because it has a high efficiency rate (20%+).  The problem is that the most efficient solar cells require large crystals of silicon, which are more expensive to grow.  Consequently, there has been a search for other, cheaper alternatives.  These have included poly-crystalline silicon.  However, researchers have begun to look at different materials.  That’s where coal comes in.

That’s also where polymer solar cells come in.  Compared to silicon-based devices, polymer solar cells are lightweight, potentially disposable, inexpensive to fabricate (sometimes using printed electronics), and flexible. They still have some problems like the fact that they tend to deteriorate in sunlight.
However, depending on the polymer used, solar cells can be tailored to be especially efficient in absorbing certain parts of light spectrum.  That means they could capture more of the energy from the sun than other types of solar cells.

The key to these cells are the types of polymers used.  And, that is where coal comes in.  Polymer solar cells use what are known as conducting polymers – they can  conduct electricity.  They can also act as semiconductors just like silicone.

This is a relatively new field and the discovery of conductive polymers earned its three discoverers the Nobel Prize in Chemistry in 2000.  One such polymer is polyaniline.  It is a plastic that is polymerized from aniline, which was discovered over 150 years ago and comes from coal tar.   There are other polymers that are being considered that have their basis in coal based chemicals too.

Although a solar cell that degrades in sunlight seems impractical, they may be ideal economically.  If the cells are inexpensive and easy to manufacture, they might be ideal to power a while array of low power personal electronics.  Since few digital gadgets last longer than a few years before being upgraded or becoming obsolete, a solar panel that doesn’t last 20 years is unnecessary.

Needless to say, a plastic that can generate energy from the sun has great potential.  One company Konarka has a product called Power Plastic that it claims can be used in umbrellas, curtains, and even buildings.  Although the efficiency is less than traditional silicon cells (9%), the ability to “tune” the plastic to certain wavelengths means it is more efficient in low light conditions and even indoors.

Polymer solar cells don’t stop there.  Since they are so flexible, there is research on turning them into a fiber that will allow woven solar panels that could be used in backpacks or even clothes.

Unfortunately, the promise of solar cells has usually failed to live up to expectations.  The biggest problem is that they can’t produce the high levels of electricity necessary for modern living.  However, we can take comfort in knowing that whether it’s traditional coal powered electricity or the latest polymer solar cells, we still need coal to power our lives.