Banking giant Citigroup recently issued a report [PDF] that ought to thrill fans of renewable energy. However, tucked inside the good news is a pill that some greens will find difficult to swallow.
The good news is that Citi expects renewable energy to triumph; it believes that typical forecasts like those from the International Energy Agency are too pessimistic. Contrary to a certain strain of conventional wisdom, it says, shale gas will not crowd out renewable energy. Quite the opposite.
The pill? Citi expects it will take lots of natural gas -- more than we're currently using, in the medium term -- to get to a power system run primarily on renewables. In fact, renewables and shale gas are in a "symbiotic" relationship, the report says, each helping the other increase market share. If that's true, a moratorium on fracking, called for by many greens, might serve to inhibit the spread of renewable energy.
There are two reasons to see renewables and natural gas as mutually reinforcing. The first and most familiar is that renewables -- at least wind and solar -- are intermittent and require backup plants that can quickly ramp on and off ("peaker" plants) to support them. Those peaker plants typically run on natural gas.
The second reason is less well understood.