The exact time depends on the characteristics of the plant and its installed capacity, but it is generally a matter of a few years. Unless it’s in a particularly arid area, building a hydropower plant is always worthwhile in terms of emissions. It is estimated that just 10 years after its construction, the difference when compared to fossil fuels is already so vast as to be incomparable, and that after 50 years of operations, the hydroelectric energy generated results in total emissions of just 13.6 grams of CO2 per kilowatt-hour, which falls to 8.1 grams after another 50 years. By way of comparison, at the beginning of the 2010s, the average was 469 grams per kilowatt-hour for natural gas combustion, 840 grams for oil and 1001 grams for coal.