It's one of the latest ways big business claims to be curbing global warming: More than 750 utilities across the country now offer customers the chance to pay a premium on their electricity bills to generate "green power." But it turns out that, in many cases, most of the money goes for marketing costs, and little can be traced to the generation of additional renewable energy.

Lisa Baker of Atlanta jumped at the opportunity last summer to protect the environment when Georgia Power invited consumers to pay extra to "help bring more renewable power to Georgia." Paying the minimum annual premium of $54 "is equivalent to planting 125 trees or not driving 2,000 miles," the utility, a unit of giant Southern Co., boasts on its Web site. Baker, a 33-year-old freelance writer, joined more than 4,000 other customers who signed up for the Green Energy program. "I wanted [the utility] to know there's a market for renewable power," she says.

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