When people talk about renewable energy, they usually mean that the main source from which the energy is derived—wind, the sun, ocean waves and tides, the never-ending heat below the Earth’s surface—is available in endless supply and either remains relatively constant or continually regenerates as part of the planet’s natural cycles.

For renewable energy to be sustainable, however, the mechanisms we use to convert the raw energy to usable power have to be just as renewable as the source from which it is drawn. Currently, most of those mechanisms—from solar cells to hydrogen fuel cells—contain enough non-renewable material to make them the weak link in the renewable energy chain.

That idea was highlighted at the Financial Times Energy Conference in London a couple of weeks ago and reported in New Scientist magazine. Solar cells convert sunlight to electricity, but the most efficient solar cells rely on indium, a rare and expensive mineral that is in short supply worldwide. Hydrogen fuel cells, among the most promising alternative vehicle-fuel technologies, require platinum, which is even rarer than indium.

Scientists are hard at work on alternative ways to make renewable energy truly renewable, by finding new ways to convert the energy to electricity or other types of power without the need for components that may not be available when needed. Unfortunately, many of those breakthroughs may be years away—and at a time when the world is looking to renewable energy to slow global warming and replace fossil fuels before supplies are exhausted. Clearly, we have a lot more work to do.

Larry’s Environmental Issues Blog

By Larry West, About.com Guide to Environmental Issues