Two things: 1. Capital expenses are quite high, even though running expenses are low. 2. It's only viable in specific geographic places, where heat is brought

Two things: 1. Capital expenses are quite high, even though running expenses are low. 2. It's only viable in specific geographic places, where heat is brought up close to the surface by magma and water flows. Otherwise you just need to drill too deep to get useful heat. So the big sites are at places like The Geysers in California, the hot springs of Iceland, and the places the site mentions in Kenya.