The charge is certainly plausible; financiers, like most people, are susceptible to fads.

But others see something much more important at play — that yieldcos represent a breakthrough for renewables: a powerful new way for wind and solar developers to raise money on the capital markets.

Considering the billions of dollars and untold number of new investors that yieldcos have delivered to the renewables sector over the past year, the question of whether they are a flash in the pan or a trend with staying power is among the most interesting facing the industry in 2014.

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