But exploration is very costly, so the African Rift Geothermal (ARGeo) fund aims to encourage investors by paying for part of the bill at sites where test drilling -- which can cost several millions dollars at a time -- comes up "dry".

"The expense of looking for geothermal is huge," Catherine Vallee, a senior UN Environment Programme (UNEP) programme officer, said in an interview. "This new facility will provide a kind of insurance scheme to mitigate against some of that risk".

Geothermal plants use steam trapped deep underground to spin turbines, creating power. The technology has attracted growing interest as rich and poor nations alike try to boost generation while reducing gases emissions blamed for climate change.

The World Bank has committed $13 million so far to the ARGeo fund, which will operate in six countries along the Rift: Kenya, Uganda, Tanzania, Ethiopia, Eritrea and Djibouti.

UNEP has contributed $4.7 million, and bilateral donors are expected to add at least another $10 million to the pot.

Kenya was the first African country to tap geothermal power, and already hosts the continent's biggest geothermal plant near Naivasha, about 140 km (85 miles) west of the capital.

The ARGeo project will seek to build on that by boosting local skills and sharing experience and exploration equipment.

"Geothermal is secure, reliable and clean energy, once set up," Vallee said. "It can really change things in this region."

Katherine Sierra, the World Bank's vice president for sustainable development, said the Bank had donated some $200 million to building geothermal capacity in Kenya over the last 30 years -- about a third of its total donations to the country.