New energy: climate change and sustainability shape a new era

RENEWABLES HAVE VICES, TOO

To feel the constant whip of winds across the Great Plains, or to bake in the endless sunlight of the American Southwest, is to imagine that these renewable energy sources are limitless.

But they aren't, says Vaclav Smil, an energy scientist at the University of Manitoba. He points to his calculations that harvesting all of the accessible power from ocean currents, tides, and geothermal heat worldwide would only replace about 2 percent of the energy that we derive from fossil fuels. Likewise, stopping up every economically harnessable river on Earth with a hydroelectric dam – an unlikely scenario – would still replace only 10 percent of our fossil fuel use. And wind – if we harnessed all of the power that can be realistically recovered at a height of 250 feet over the Earth's surface – might replace 10 or 20 or 30 percent of our fossil fuel use.

Of all of the renewable energies, says Mr. Smil, only solar can do the job single-handedly. Capture just 1/1000th of the sunlight that reaches our planet's surface and we could replace our entire use of fossil fuels.

Even if solar and wind have the greatest potential, we'll need a diverse mix of renewables. Iceland has poor sunlight, but could do well with geothermal energy. Norway and New Zealand have done well with hydroelectric power. And in rural Asia and Africa, low-tech thermal reactors could convert agricultural wastes such as wheat chaff into gaseous fuels.

These measures might relegate oil spills and mountaintop removal to memory. But they'll create new challenges of their own.

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