You would want to look at lifecycle analysis studies (here's a few [1][2]). The big problem with fossil fuel is that it takes fuel to extract new fuels (high cost sources like tar sands have a ratio of like 1 fuel unit used to extract 2) AND they have a cost for each unit of power generated. Most renewables (excluding biofuels for example), have a manufacturing cost, but little to no energy generation cost (solar and wind have none, hydropower basins have something like 1/1000th the emissions of coal).
[1] http://phys.org/news/2014-10-first-ever-global-life-renewabl...