New options for solar power

July 19, 2009

New Options for
Solar Power
We need cheaper and more
diverse solutions

Harley L. Sachs 7/20/09
Solar panels can be as small as the tiny one on your light-charged pocket
calculator; but there are new developments that promise to provide more
significant supplies of electricity. What’s new are more efficient
collectors and alternatives to the silicon wafers we’re seen before. We’ve
come a long way from the 1954 photovoltaic (PV) cell developed by Bell
labs.
Some years ago, an Israeli professor at Michigan Technological University
was ready to give up on solar energy. His view was that the amount of
energy that fell on a given acre of land was insufficient to generate
enough electricity. He felt that solar power converters needed to cover
the earth with solar collectors, leaving no room for other development. It
looked like one needed places like the Negev Desert to provide enough
space and sunlight for the placement of acres and acres of solar
collectors.
Instead of direct conversion to electricity, an alternative is to focus
the heat from the sunlight and use it to power electric generators. In the
Nevada desert several installations were built that focused the sun’s rays
on a boiler, heated it to 400 degrees Centigrade and ran steam turbines.
Unfortunately, the Nevada generators use only 20 percent of the sun’s
energy and could not compete with coal.

STIRLING ENGINE
An alternative that takes up less land surface than what the Israeli
engineer visualized is a tower surrounded by focusing mirrors. The heated
fluid in the tower in a high pressure boiler is used to power a Stirling
engine. The Stirling engine, first patented in 1816, is efficient. The
next step is to collect enough solar energy during the day to keep
electricity generating when the sun is down. A solar collector that
focuses the light to boil water -- which then turns a steam turbine --
doesn’t hold the heat long enough. Something that doesn’t cool as quickly
is needed.
A solution of salts, like a mix of sodium nitrate and potassium nitrate,
can be heated to 600 degrees Centigrade. That stored heat can last long
enough to create steam for a turbine even after the sun is down.
The panel that converts light directly to electricity is not dead. To keep
production costs down, something more efficient than a flat panel had to
be invented.
A California company called Soliant Energy has created a solar collector
which needs less expensive photovoltaic material than most converters.
Instead of a flat panel, the company uses open, half-pipe cylinders with
plastic lenses that focus the sunlight on a central PV strip. Always
turned toward the sun, the half-pipes’ lenses maintain maximum exposure
during the day. Of course, they don’t generate power at night.
But can solar generated electricity compete? The average cost of
generation using conventional methods is 10 cents per kilowatt while solar
has been twice that. A new California company claims they can generate
energy for 3 cents a kilowatt; if true, that might solve the efficiency
problem.

BIG NEEDS
Unfortunately, what may work in the laboratory on a small scale may not
translate to large scale manufacturing. Fifty percent efficiency can be
achieved in an experiment, but if it’s too expensive it may be like
running your diesel engine on Chanel #5 - possible, but not practical.
The manufacture of some PV panels involves toxic chemicals and waste
that’s expensive to dispose of. If we factor in the cost of cleaning up
the pollution a product generates, can we afford it?
In the past those costs have been simply passed on to the next generation,
like the toxic cleanup needed in the copper country of the Upper Peninsula
to undo the damage done when the mines and smelters were active. They’re
gone, but the waste remains. Like the wilderness tourist who takes only
pictures and leaves only footprints, whatever means we devise to satisfy
our energy demands must leave no mess behind and not destroy the
environment.
One possibility for solar power generation is a new form of plastic that
conducts electricity. Though not as efficient as the PV panels we’re
familiar with, when it comes down to cost of manufacture versus final cost
per kilowatt, this may be the one that works.

CUT COSTS
A solution may be a really cheap form of solar panel. If it’s cheap
enough, even only a six percent efficiency can make it viable. Imagine if
the siding on your house could generate all your power needs! For
instance, if your house had siding that generated electricity, even if the
efficiency were low, the volume might be enough.
The choice seems to be between a great many solar chargers working at a
low efficiency versus a few much more expensive devices that work at 50
percent efficiency. Ultimately, none of the non-polluting alternative
means of generating electricity -- be they windmills, hydroelectric dams,
generators working off ocean swells, or solar power -- will be enough to
satisfy our gluttony for energy, but in combination they will.
Imagine that little solar charger on your calculator expanded big enough
to power your refrigerator and charge the batteries of your electric car;
in the 1970s we got special tax breaks for insulating our homes, etc.
Maybe it’s time to revive that method to encourage solar power
generation.

Visit the web site www.hu.mtu.edu/~hlsachs where you can listen to two
stories, read a third, read reviews, and find links to the publishers of
my books.