North of Nairobi, for example, the lush, farm-laced hills gradually give way to the semiarid landscape of the Laikipia District, 2 million acres framed to the east by Mount Kenya, to the south by the Aberdare Mountains, and to the west by the fossil-rich Great Rift Valley.

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The ash is a waste product of the Kingston Fossil Power Plant which is operated by the Tennessee Valley Authority.

NPR: In Tenn. Town, A Muddy Christmas For Some

In contrast to the depletion economics that drive up the cost of fossil fuels over the long run, solar power is a Silicon Valley-style energy resource: the more we make, the more we learn, innovate and lower the cost of the technology.

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