Roughly, it took 50 years for coal to replace wood as a major energy source. It then took about 50 years for oil to replace coal for most applications. Solar and wind will probably happen much more quickly. Technological change is accelerating the supply. Societal awareness is accelerating the demand. Renewables may not arrive quickly enough to stop global warming, but global warming will be moderated in proportion to the rise in renewables and the decline in fossil fuels.