THE Great Rift Valley in East Africa is set to become the world’s biggest source of geothermal energy. Engineers, governments and bankers agreed last month to press ahead with an ambitious renewable energy programme that will use a new generation of remote sensing technologies to pinpoint the best places to tap the Earth’s heat.
The valley was created when a chunk of the Earth’s crust 4000 kilometres long sank between a pair of parallel fault lines. The rocks beneath the valley are still heated by volcanic activity and have the potential to provide around 7000 megawatts of electricity-generating capacity, which is the equivalent of a dozen or more large, coal-fired power stations. If fully exploited, the valley would almost double world output of geothermal energy.
For 20 years, 33 wells sunk into the Olkaria geothermal field west of Nairobi have tapped steam held under pressure around the hot rocks to generate up to 45 megawatts of electricity, enough to supply around 5 per cent of Kenya’s demand. The country has baulked at further investment because of the expense of drilling new wells, and uncertainties about precisely where to drill them.
Advertisement
At a meeting in Nairobi last month, technologists from the World Bank and the UN Environment Programme said that a combination of remote sensing methods, known as “joint geophysical imaging”, could transform the valley’s energy-generating potential by locating the hottest, wettest and most accessible rocks. The technique can identify cracks in rocks and the presence of hot water and steam at depths of a kilometre or more by mapping micro-earthquakes and measuring the electrical resistance of the rock.
The cost savings of eliminating even one or two uneconomic production wells will “dramatically reduce geothermal development costs”, says Mohamed El-Ashry, chairman of the World Bank, which is funding the plan.
The first target is a zone of geothermal energy thought to lie beneath Longonot, a volcano close to Olkaria. It could be generating one-third of Kenya’s electricity within 15 years.
Kenya’s neighbours also want to get in on the act. Ethiopia commissioned its first geothermal plant four years ago. And up to a dozen other nations along the valley as far south as Mozambique could soon join the rush.
UNEP and the World Bank see cheap power from hot rocks as a way for Africa to industrialise without using more fossil fuels, at a time when climate change is making hydroelectricity increasingly unreliable. Tapping geothermal energy also releases toxic gases such as hydrogen sulphide, and measures would be needed to ensure that the geothermal power plants do not harm valley wildlife.