SINCE 1904, when Prince Piero Conti managed to get a light bulb to flicker in an Italian lava field, geothermal power has depended on volcanic heat. The earth's crust needs to be thin, with high temperatures just below the surface. Cold water is pumped down a deep borehole and returns superheated to spin a turbine. To power its tiny and now spluttering economy, Iceland has already made use of what scientists call volcanism. Fiery bits of the Philippines also run on geothermal power.

So what about Africa? The continent's lack of electricity is a big deterrent to foreign investors, as demand for power grows by 8% a year. Some experts think the Rift Valley, which stretches from the northern end of the Red Sea down to Mozambique, is ideal for generating geothermal power.

This has many advantages. Geothermal power runs whatever the weather, making it ideal for providing the base power station of a national grid. It emits negligible carbon compared with fossil-fuel stations. Best of all, it offers indigenous power cheaply: east Africa sorely lacks west Africa's oil or the potential for solar power in the Sahel, Africa's wide belt just south of the Sahara desert. The United Nations Environment Programme, which has its world headquarters in Kenya's capital, Nairobi, thinks the geothermal potential of the Rift Valley is 14,000MW, yet only 200MW is currently captured. Aficionados of geothermal power say it could provide 10-25% of the region's energy by 2030.

But the technology has snags. It would create few jobs, a fact that turns off many African politicians, who tend to like national projects to be labour-intensive. It disrupts pastoralists herding their cattle and can leak radon and other gases. Its start-up costs are as high as drilling for oil, and may be higher than for coal power stations. So the World Bank has set up a geothermal fund to underwrite exploration in east Africa. If the Kyoto treaty on carbon emissions is rewritten, Africa may get cheap loans and know-how to help install more geothermal power stations.

Some 18 geothermal sites in the Ethiopian part of the Rift Valley and in the Danakil depression on the border with Eritrea and Djibouti have been identified. The Ethiopians hope for 440MW of geothermal power against their present energy capacity of 790MW. Geothermal could be an alternative to hydroelectric dams, which provide most of the region's power but are vulnerable to drought. Djibouti has signed a deal with Iceland to build a geothermal plant near the Dantean furnace of Lake Assal, the continent's lowest point. The project will also capture steam for use as water in the parched country.

Kenya is Africa's geothermal pioneer. Its Olkaria station outside Naivasha already produces 158MW. The government says it wants to raise its geothermal capacity to 576MW within a decade. That could make a big difference. Kenya already uses up all its 1,200MW capacity and is compensating for frequent power cuts by installing temporary diesel generators.