Multijunction Solar Cells - Overview and History

Ultimately, all energy - even energy derived from fossilinexpensive compared to the rest of the country.
fuels - is solar energy. The difference betweenOne of the keys to this bright energy future is
petrofuels and what we think of today as solar energymultijunction solar cells. These cells have multiple layers,
is that the former represents the sun's energy that haseach of which is "tuned" to a different part of the sun's
been locked up in the form of carbon for hundreds ofspectrum. As you may know, the sun's rays are made
millions of years and is released when it is burned.up of different colors, which you can see through a
New technology such as solar photovoltaic cells makeprism or after a storm when water droplets in the
direct use of solar energy as it reaches the surface ofatmosphere break up the spectrum, producing a
the planet. Although this is virtually pollution-free andrainbow. Each layer in one of these specialized cells
can ultimately provide virtual no-cost energy, therecaptures part of the spectrum - which means they are
have been two major drawbacks to photovoltaic solarable to capture more of the sun's light and turn this into
cells: cost and inefficiency. Solar cells have historicallyelectricity.
been exorbitantly expensive, and generate relativelyThe bottom line is efficiencies up to 40% - 4-3 times
little in the way of usable electrical power.that of older types of solar panels.
However, as has been the case with the personalMultijunction solar cells have been around for awhile,
computer, solar energy technology is undergoing rapidbut until now, costs have been astronomical - literally.
changes that allow solar voltaic cells to produceThey have long been used for orbiting satellites (and
greater amounts of energy at much lower costs;are used on the Mars Rover as well), because their
barring interference from federal legislators and oillight weight went a long ways toward offsetting the
company lobbyists, it is very possible that within thecost of getting them into outer space. Today, scientists
next few years we will be able to generate electricityat the U.S. Department of Energy Renewable Energy
from solar panels for as little as.03c a kilowatt - aboutLab have achieved more than 40% efficiency using
half of what folks are paying for hydro power inthis technology, which is currently the record for such
Washington State, where electricity is alreadygeneration.