A wealth of scientific publications covers the overall balance of the carbon footprint created by geothermal plants. What is certain is that geothermal energy entails a considerable reduction of emissions compared to fossil fuels; the picture, however, is more complex when we compare it to other sources of green energy. The power plants’ construction phase, indeed, has to account for the construction of the buildings themselves as wells the energy required to drill and reach the heat source underground.
Nevertheless, the signals emerging from quantitative analyses are clear. Over the course of a geothermal plant’s lifecycle, a few dozen grams of carbon dioxide are released in the air for every kilowatt-hour of energy produced; depending on the studies and the kind of plant technology, this amount can vary from 15 to 180 grams per kilowatt-hour. There is no comparison between geothermal and fossil sources: in the early 2010s, natural gas released on average 469 grams per kilowatt-hour, oil emitted 840, and coal a staggering 1,001. Even if technological progress is slowly lowering these values, geothermal energy still ensures a definitely greener performance.