Despite what shortsighted critics say, solar power is the wave
of the future . . . and–of course–it’s been the basis of our
energy supply all along, since most of our current power sources
would not be available today if it weren’t for of Sol.
Unfortunately, the process of converting sunlight directly into
electricity–which is the form of energy most useful to us–by
means of solar cells has been prohibitively expensive . . . until
now!
That’s right . . . just recently, a genuine breakthrough
in photovoltaic technology pioneered by a research arm of
the Radio Corporation of America (RCA) has brought affordable solar power in reach. They’ve made it possible to reduce
the cost of sun-produced electricity from an average of $10 a
watt to $1.00 (or less) for that same watt . . . which,
unbelievably enough, is even less expensive than some
utility-supplied power!
Age-Old Technology
The truth is, photoelectricity has been around for some time.
It was first recognized in 1839, and was eventually developed
into a useful source of energy with the advent of wafer-type
solar cells in the mid-1950’s. In a nutshell, a conventional
photovoltaic cell works like this: A semiconductor material (in
this case, silicon, which is a component of sand and is thus
plentiful) is first refined to a high degree of purity in an
electric furnace. Next, this 99% pure material is “cleansed” even
further through various chemical processes, and is then
converted under intense heat from a granular form into a
single-crystal state.
During the conversion process, the silicon is “doped” with
either boron or phosphorus to form P (positive) or N (negative)
ingots. The impregnated crystals are then sliced very thin and
joined, P to N, using a doping agent and more heat. With that
done, minute nickel or aluminum strips are attached . . . to
conduct current and act as terminals. When sunlight penetrates
the thin P-layer, a reaction takes place in the “barrier”
between the P and N layers and electricity is produced.
Obviously, then, the cost of manufacturing a wafer-type solar
cell can be quite high. Besides the expense of merely
producing the necessary ultra pure silicon, the
substance must be further processed by physically slicing the
ingots . . . then each cell must be assembled, which also
increases cost. So, not only are the necessary materials at a
premium, but the manufacturing steps themselves run into big
dollars.
The Secret’s in the Sauce
How, then, has RCA broken through the price barrier? To put it
simply, the firm has attacked the problem from a whole new
direction. Conventional photoelectric cells are
relatively effective in terms of light-to-power conversion,
achieving an impressive 10% (or higher) efficiency in the field.
However, to achieve such a high rate of efficiency, the cells
must be manufactured from only the purest grade silicon . . .
anything less simply wouldn’t yield the magic number.
RCA researchers decided to try a different approach: If
manufacturing costs could be reduced drastically, they reasoned;
cell efficiency would no longer be of prime importance. So, as
early as 1974, RCA technicians began developing what they call
hydrogenated amorphous silicon cells . . . hardware that not only
uses inexpensive “impure” silicon, but requires less costly
manufacturing techniques as well.
According to Dr. David Carlson, group leader of RCA’s
photovoltaic research team, the fabrication process is completely
different from that used for conventional single-crystal silicon
solar cells. “We start with a gas called silane, which consists
of silicon atoms surrounded by four hydrogen atoms, and we use an
electrical pre-charge–much like that in a fluorescent tube–to
break up the silane molecules and deposit a film containing
between 5 and 50 percent hydrogen by atomic weight. In other
words, the hydrogen is chemically bonded into the silicon . . .
and it’s the hydrogen that makes the cells work. Prior to our
discovery, it was generally accepted among scientists in
photovoltaic research that you couldn’t use amorphous, or
noncrystal, silicon semiconductors to make solar cells because
there were too many broken bonds in the ‘impure’ structures. But
it turns out that the hydrogen ‘heals’ such defects and makes the
material a fairly good semiconductor.”
Of course, less costly silicon is only part of the story . . .
the fact that the new process minimizes production costs is just
as important. Since the gas and precharge technique doesn’t
require intense heat (necessary temperatures have been reduced
from over 1,400°C to 200°C), not only is less energy
consumed in production, but many types of inexpensive material
(including glass, sheet metal, and even plastic) can now be used
as a base or substrate . . . where only a high grade of metal was
acceptable before.
In addition, the innovative method cuts corners by
combining processing steps. The substrate section is
first coated with a very thin steel or titanium conductive layer,
then alternate P- and N-doped layers-sandwiched around a “spread”
of undoped silane about half a micron thick -are deposited. (The
beauty of working with a gas, by the way, is that different
layers can be “painted” on . . . and the “dope”–in this case
phosphine and diborane gas–can easily be premixed with the
silane.) The final step involves coating the structure with a
transparent conductive oxide-Indian tin-which naturally carries
electricity and allows light to pass through. The entire
process is so relatively quick and easy (it may take anywhere
from 1 to 20 minutes) that it makes the production of
“old-fashioned” single-crystal silicon cells almost impractical .
. . and, even more important, cuts costs to the point where the
glass substrate is the most expensive material used.
Efficiency is the Key
Before the company goes into full swing with the amorphous
silicon solar cell program, its people would like to increase the
efficiency of the little converters. So far, researchers have
managed to reach a conversion factor of nearly 5% . . . which
would put the cells in the range of $1.00 per peak watt for large
quantities-right now. Carlson hopes, however, to be able to
increase that percentage in the near future . . . since the
material they are working with now is capable of about
an 8% efficiency. (He also claims that in the next few years a
10% efficiency will likely be achieved.)
Today RCA . . . Tomorrow the World
Naturally, the effect that the mass production of inexpensive
photovoltaic cells could have on society as a whole is nothing
short of mind boggling. Since such devices will be well within the
financial reach of the average American family, it isn’t
inconceivable that in the near future rooftops all across the
nation will be covered with arrays of the 3″ X 3″ miniature
generating stations. The energy provided by photovoltaic cells
can, of course, be utilized in several ways . . . either totally
independent of the local utility by adding battery storage
(perhaps in combination with electrically heated water storage
for space heating if desired), or–on a limited scale–in concert
with the power company . . . by swapping that utility’s energy at
night for solar electricity during the day.
But that’s not all . . . since the cells are capable of
functioning even under adverse conditions (RCA researchers find
their creations can produce between 20 and 30% of total power on
an overcast day), future possibilities include using them as a
source of power for electric propulsion vehicles (in conjunction
with lightweight batteries for nighttime use).
What it all boils down to is that tomorrow’s dream is here
today . . . and it shouldn’t be long–perhaps two years or
less–before we all can enjoy low-cost, independently
produced electricity!
EDITOR’S NOTE: New developments in photovoltaic research
within the past few months may make it possible for us all to
enjoy energy independence in the very near future: Keep a weather
eye posted toward MOTHER EARTH NEWS’ pages, because in the next few issues
we should be reporting on several other pioneering groups who
are on the verge of making similar momentous discoveries.
