I've heard that solar cells actually consume more energy than they produce. Is that true?

Gil: As Amory Lovins notes in his 2003 paper 20 Hydrogen Myths:

"Any conversion from one form of energy to another consumes more useful energy than it yields. If it could do the opposite, creating energy out of nothing, you could create a perpetual-motion machine violating the laws of physics. Conversion losses are unavoidable; the issue is whether they're worth incurring."

Which is to say: How does their energy yield compare with other available options?

In the specific case of PV (photovoltaics), the U.S. Department of Energy states in item #6 of its informational article "The Myths of Solar Electricity":

"The energy payback period is... dropping rapidly. For example, it takes today's typical crystalline silicon module about four years to generate more energy than went into making the module in the first place. The next generation of silicon modules, which will employ a different grade of silicon and use thinner layers of semiconductor material, will have an energy payback of about two years. And thin-film modules will soon bring the payback down to one year or less. This means that these modules will produce 'free' and clean energy for the remaining 29 years of their expected life."

With technology investments, as with financial investments, the key is the return on that investment. And the key to understanding your ROI is making sure that all relevant data is included; in the case of energy economics, including the energy costs of the entire life cycle or supply chain -- extraction, refining, transport, (and, in the case of nuclear power, plant decommissioning and long term waste storage) -- is essential to getting a meaningful ratio. (If you'd like to read more, try this [currently disputed] Wikipedia entry, and the discussion that it's generated.)

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Gil Friend, systems ecologist and business strategist, is president and CEO of Natural Logic, Inc. -- offering advisory services and tools that help companies and communities prosper by embedding the laws of nature at the heart of enterprise. Sign up online to receive his monthly column via email. Read Gil's blog here.