Solar Cell Efficiency

banner6Solar cell efficiency has increased significantly since the invention of the modern silicon solar cell.  The silicon solar cell was invented at Bell Labs in the 1950’s.  On April 25, 1954, Bell Labs demonstrated the first silicon solar cell.  It was about 6% efficient, converting 6% of the sun’s energy that struck it to electricity.

This was huge advance over the previous generation of solar cell, the selenium solar cell.  Selenium solar cells were only 0.5% efficient.  You read that right, they converted ½ of 1 percent of the energy in sunlight to electricity.  The silicon solar cells invented at Bell Labs were an order of magnitude more efficient than the selenium cells.

Since then, research has focused on both increasing solar cell efficiency and decreasing manufacturing costs.  Using exotic materials in the research lab, cells with up to 40% efficiency have been produced.  Unfortunately, producing these high efficiency cells in low quantities can cost 100 or more times what the 8% efficient amorphous silicon cells in mass production cost, but only produce about 4 times the electricity.  In order to increase widespread adoption of solar power, production cost has become as important, if not more important, than efficiency.

The sun delivers 1,000 watts of power per square meter at noon on a clear day at sea level.  This scientific definition of the sun’s power is how different types of solar cells are compared.  This measure is what one might expect under ideal conditions and can vary based on dust, pollution, elevation and temperature.  Things like volcano eruptions can reduce sunlight worldwide for a year or two.   Higher elevation actually increases solar cell efficiency.  Higher elevation means less air, dust and pollution between the sun and solar cells so less of the sun’s power is filtered out before it hits the cells.

Currently, solar cell efficiency for commercially available multicrystalline cells is about 14-19%.  This is significantly higher than the 6% efficiency of the first silicon solar cells, but this is fairly mature technology and the efficiency of this type of cell is not expected to increase much.  Amorphous silicon cells are currently about 8% efficient, but increasing the efficiency of amorphous technology is currently an area of much research.

So, assuming efficiency doesn’t improve significantly, what would it take to replace all of the fossil fuel based energy production in the United States and convert entirely to solar power?  Using commercially available solar panels and power inverters, supplying all the electricity currently produced in the United States would require a little more than 10,000 square miles of solar panels.  There is plenty of unused desert in the US that could be used for this purpose.

Now, people like to use electricity at night as well as during the day so some form of power storage would also be required.  Putting banks of batteries either in homes or close to homes is the most logical solution and these kinds of “smart grid” systems are currently being tested by power companies to solve the problems of elastic demand.  More power is used by air conditioners and other appliances during the day so power companies hope to store energy in batteries to be used to offset increased demand during the day.  These same batteries, however, could also be used to store energy from solar power during the day to be used at night.

Solar cell efficiency has increased dramatically over the past 60 years, from 0.5% to as much as 40%.  While mass production solar cell efficiency is not expected to increase significantly in the near future, solar prices continue to fall.

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