When applied universally, its a fuckin' disaster, when applied where all the key factors align it can be highly efficient. Geothermal is the best example, essentially it's free energy at the cost of infrastructure, but the only places its reasonably efficient are in northern europe and northern japan AFAIK. Solar makes a hole lot of sense in equatorial and desert nations, but people who think it's efficient in a place like Scotland should be removed from the gene pool. Hydro electric and wind both work great if you build them in the right places but the damage to local ecology can be mighty fucking bad so that further narrows the places they should be. The problem with green energy was the upfront cost a decade back so they figured economies of scale should fix that but nobody did the research on materials costs. Now it looks like that strategy will prevent green from ever really being green.