energy bursts
Solar Max
The promise of solar
energy—harvesting power that falls free from the sky—has always
run into one hard problem. Photovoltaic cells are not very efficient at
turning sunlight into electricity. For every 100 watts of power that falls
on a surface, a typical solar cell can produce only 8 to 12 watts of electricity.
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| These photovoltaic panels are part of a 5 kW solar power system at Edwards Air Force Base. |
A 5 kW power system recently installed at NASA's Dryden Flight Research
Center, at Edwards Air Force Base in California, may change all that.
The power system uses photovoltaic cells that are 20 percent efficient.
Such cells may prove to be cheaper and more compact than conventional
cells.
The cells, manufactured by SunPower Corp. of Sunnyvale, Calif., made their
efficiency gain, in part, by exposing more light-gathering surface to
the sun. Unlike conventional solar cells, the electrical contacts are
all on the back surface. This enables the cells to collect as much as
50 percent more energy per square inch than traditional photovoltaic cells.
The power system at Dryden is the first full-scale installation for the
new cells, but it isn't the first NASA project for SunPower. Another type
of solar cell produced by the company powered Helios—an unmanned
aircraft that set an altitude record of 96,863 feet.
Dropping Mercury
Coal
is getting more attention as a fuel source than it has received in years.
The United States has plenty of the stuff, and its price has none of the
variability of oil and natural gas.
But burning coal has some rather dire environmental consequences. In the
U.S., for instance, coal-fired power plants are the largest unregulated
source of mercury emissions and are responsible for approximately 40 percent
of the country's industrial emissions.
The Environmental Protection Agency estimates that U.S. power plants account
for about one-third of the mercury deposited in the country.
But must coal and mercury go hand in hand? A recent study commissioned
by Northeast States for Coordinated Air Use Management, a nonprofit association
of air quality agencies of northeastern states, indicates that mercury
emissions from power plants could be reduced by more than 90 percent by
combining existing air pollution controls and commercially available mercury
reduction technologies.
The report states that existing emission control technology designed to
reduce sulfur dioxide and particulate matter can deliver simultaneous
substantial mercury reductions. This side effect could enable plants to
meet a more restrictive mercury standard even if the emissions controls
are not specifically optimized for the metal.
In addition, the report found that activated carbon injection, a technology
used in municipal waste combustors, can achieve mercury emissions reductions
of more than 90 percent. The report recommended adapting activated carbon
injection for use in coal-fired boilers to achieve similar reductions.
Already, there have been a number of successful pilot and full-scale demonstration
projects that prove the transferability of this technology.
H2 Uh-Oh
Many environmentalists
are looking forward to the arrival of the so-called hydrogen economy.
The tailpipes of hydrogen-fueled cars, after all, would spew only water
vapor. But a recent study from researchers at the California Institute
of Technology in Pasadena has pointed out a potential flaw in this green
dream: Leaked hydrogen gas might well damage the upper atmosphere.
No one knows just how much hydrogen would escape the pipelines, storage
tanks, and refueling centers of a national-scale hydrogen infrastructure.
But if losses ran 10 to 20 percent, the researchers estimated that an
all-hydrogen economy would leak around 100 million tons of hydrogen a
year into the atmosphere—about seven times as much as is currently
released by human activity.
This added hydrogen would alter the chemistry in the stratosphere, where
ozone is created. A reduction in atmospheric ozone would lead to higher
influxes of ultraviolet radiation.
The authors of the study stress that this in itself is no reason to turn
away from hydrogen as a form of fuel. Instead, they say, engineers should
be mindful of the potential harm as they design the parts of the hydrogen
infrastructure.
This section was written by Editor Jeffrey Winters.