Verdant hills, Kenya, stretch into the distance at Hell’s Gate National Park, where zebras, buffalos, antelopes, baboons and other wildlife roam an idyllic landscape of forests, gorges and grassy volcanoes near the shores of Lake Naivasha. Snaking over the same landscape are pipes. Miles and miles of pipes — some high enough off the ground that trucks can pass underneath and giraffes won’t hit their heads — carry steam from beneath this volcanic valley to big power plants inside the park.The valley’s animal herders have long known the unusual properties of the ground under their feet. On chilly days, they warmed themselves near vents that emit plumes of hot steam. Now, Kenya is increasingly harnessing that steam to turn generators that can allow it to expand electrical service and power its rapidly growing economy.