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Catching Some Rays
By Sarah Webb / July 2, 2007
Harnessing the power of the sun is nothing new. People have had solar-powered
calculators and buildings with solar panels f or decades. But plants are the real
experts: T hey’ve been using sunlight as an energy source f or billions of years.
Cells in the green leaves of plants work like tiny f actories to convert sunlight,
carbon dioxide, and water into sugars and starches—stored energy that the plants
can use. T his conversion process is called photosynthesis. Unf ortunately, unless
you’re a plant, it’s dif f icult and expensive to convert sunlight into storable energy.
T hat’s why scientists are taking a closer look at exactly how plants do it.
Plants such as this sunflower efficiently convert the sun’s light into energy that they can use.
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In a world with increasing energy needs, researchers are always looking f or new ways to power everything
f rom cars to computers without putting more stress on the environment. T hat’s another reason why
scientists are so interested in solar power—it doesn’t pollute the air, water, or land. And since the sun lights
and warms the entire planet, the ability to harness its energy could provide a clean energy source f or
everyone.
Focusing on fuel
T he main sources of energy that people use today are called f ossil f uels, such as natural gas, oil, and coal.
Unf ortunately, the supply of f ossil f uel is limited. Once we use all the coal and oil in the Earth, they’re gone
f or good. T he sun, on the other hand, is a renewable energy source. No matter how we tap it f or energy, the
sun will be around—at least f or the next f ew billion years.
T here’s another problem with burning f ossil f uels—pollution. T he ideal energy sources of the f uture will be
“clean”: they won’t produce carbon dioxide and other gases that pollute the environment as f ossil f uels do.
The air pollutants spewed by this oil refinery illustrate one drawback to relying on energy from fossil fuels.
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Hydrogen is one alternative to f ossil f uels that interests many researchers today. Hydrogen burns clean—it
produces only water, not carbon dioxide. Researchers are trying to come up with ways to make large
quantities of hydrogen cheaply and cleanly, and one way involves using plants or plant-like organisms, such
as algae.
Putting plants to work
Some scientists are trying to get plants, or biological cells that act like plants, to work as miniature
photosynthetic power stations. For example, Maria Ghirardi of the National Renewable Energy Laboratory in
Golden, Colo., is working with green algae. She’s trying to trick them into producing hydrogen instead of
sugars when they perf orm photosynthesis. Once the researchers can get the algae working ef f iciently, the
hydrogen that they produce could be used to power f uel cells in cars or to generate electricity.
The algae (green) are grown in flasks to produce hydrogen in the lab.
Courtesy of DOE/NREL, Warren Gretz
During photosynthesis, plants normally make sugars or starches. “But under certain conditions, a lot of
algae are able to use the sunlight energy not to store starch, but to make hydrogen.” Ghirardi says. For
example, algae will produce hydrogen in an airf ree environment. It’s the oxygen in the air that prevents algae
f rom making hydrogen most of the time.
Working in an airf ree environment, however, is dif f icult. It’s not a practical way to produce cheap energy. But
Ghirardi and her colleagues have discovered that by removing a chemical called sulf ate f rom the environment
that the algae grow in, they will make hydrogen instead of sugars, even when air is present.
Unf ortunately, removing the sulf ate also makes the algae’s cells work very slowly, and not much hydrogen is
produced. Still, the researchers see this as a f irst step in their goal to produce hydrogen ef f iciently f rom
algae. With more work, they may be able to speed the cells’ activity and produce larger quantities of
hydrogen.
Maria Ghirardi observes one of her algae reactors.
Courtesy of DOE/NREL, Warren Gretz
T he researchers hope that algae will one day be an easy-to-use f uel source. T he organisms are cheap to
get and to f eed, Ghirardi says, and they can grow almost anywhere: “You can grow them in a reactor, in a
pond. You can grow them in the ocean. T here’s a lot of f lexibility in how you can use these organisms.”
Making sun catchers from scratch
Other scientists interested in alternate f uel sources are also f ocusing on plants. But these researchers want
to re-create what plants do without actually using them.
Plants have molecules that catch and store solar energy. Scientists want to create molecules that mimic what
plant molecules do.
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Plants have specif ic molecules that catch the energy of sunlight during photosynthesis. Some biochemists
have used special techniques to take a snapshot of these molecules inside a cell. “We f inally know what the
little f actory looks like,” says Daniel Nocera, a prof essor of chemistry at the Massachusetts Institute of
Technology (MIT ).
Chemists in Nocera’s lab have an ambitious plan to capture the sun’s energy. Instead of tweaking the suncatching molecules f ound naturally in plants and algae, these researchers want to build artif icial suncatching molecules f rom scratch. “We’re all busily working away to try to f igure out how to make
[photosynthesis] happen outside of the leaf ,” Nocera says.
T heir goal—even though it is still many years away—is to have the artif icial molecules produce hydrogen f or
everyday use.
Sunlight is already Earth’s chief energy source. If humans can learn to harness solar energy more efficiently,
sunlight will provide even more energy than it does now.
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Finding solutions to our energy problems is one of the great scientif ic challenges of our time, Nocera says.
But it’s the challenge of the unanswered questions that keeps him excited about his work. “It’s like we need
to paint a picture,” he says. “At some points, we don’t even have the paints yet.”
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