Bill Gates' latest clean energy investment gives a whole new meaning to the term "natural gas." The Gates Foundation is putting $1.5 million towards developing a "Next-Generation Urban Sanitation Facility" in Accra, Ghana. The facility takes human poop and turns it into biodiesel and methane, the same stuff natural gas companies are so eagerly pumping out of the ground lately.

Besides the "wow" (or "ick") factor here, there's the unabashedly good-for-the-world part: even aside from providing frack-free natural gas power, facilities like these could keep human waste from contaminating water sources and spreading disease.

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