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Reaping the sun

Each day, the sun pours 15,000 times more energy on Earth than what we produce from fossil and nuclear sources, writes Prakash Chandra.

india Updated: Aug 21, 2006 03:32 IST

For a farmer, Heiner Gartner is unique: he reaps the sun. The fields on his 80-hectare farm in Buttenwiesen, Germany, are covered not by crops, but by thousands of solar panels that soak up sunlight and convert it into electricity for nearby villages.

Sunlight is the planet’s fastest growing energy source, powering everything from calculators and cars to satellites and spaceships. Each day, the sun pours 15,000 times more energy on Earth than what we produce from fossil and nuclear sources.

Solar cells, or photovoltaics (PVs), that generate electricity from sunshine range from tiny batteries to very large systems that provide thousands of kilowatts of power. PV technology is not unlike transistors that drive modern electronics. A sliver of silicon is doped with traces of other elements so that the ‘impurities’ produce more electrons on one surface of the wafer and make it more negatively charged than the other, creating an electric field.

When a photon hits this field, some electrons are displaced, prompting other electrons to move between the crystal’s two sides and setting off an electric current that flows through the circuit joining the surfaces.

Scientists develop PVs from various materials. Plastic PVs are inexpensive, but their lifespan gets shortened when exposed to sunlight. Semi-conducting plastics are a better option. Cheaper than silicon and more flexible, they make it possible to ‘print’ solar cells onto different surfaces.

Latest research focuses on PVs made of inorganic nanocrystals. A thin layer of electron-rich cadmium telluride is deposited atop electrically conductive glass and covered with a film of electron-hungry cadmium selenide. The stack is then topped off with conductive aluminum. Exposed to sunlight, the electrons in this PV generate a powerful current as they move through the nanocrystal layers to the aluminum contact.

The world will need 30 terawatts (30 trillion watts) of power, preferably carbon-free, by mid-century. This may encourage more farmers to emulate Gartner and turn scientists. Some scientists could turn farmers as well —  to ‘harvest’ the sun in Earth-orbit using space solar power (SSP) satellite technology.

These ‘powersats’ would catch the sun’s energy and pump it via microwave beams to Earth, where converted to electricity, it’d fed into power grids. But advanced composites and robotics will be needed to till these extraterrestrial PV fields. Beaming even 10 terawatts of power to Earth would involve 660 SSPs, each the size of a dozen football stadiums! Wonder how long before breakthrough technologies switch on this in-orbit power plug.