The Democratic Party 2016 Platform pledged to end the use of fossil fuel by 2050.
Total elimination of fossil fuels in the US by 2050 would require prohibiting emissions from fossil fueled vehicles, civilian and military airplanes, military tanks and other vehicles, home heating and air conditioning, lawnmowers and other gasoline-powered yard equipment, earth moving equipment, and electrical generation.
In an isolated area of South Korea, the local power company experimented with eliminating the use of fossil fuels for generating electricity.
They paid for solar energy and wind energy capacity three times higher than the highest previous usage, and four times average usage.
They installed a large battery to hold enough energy for over a day of ordinary use.
The experiment was a failure -- they were forced to use backup diesel generators for more than half of all electricity (not enough wind and sun).
The sun usually does not shine, and the wind usually does not blow, when electrical demand happens to be high.
The cost of (if paid by the South Korean residents), would have averaged $1,100 per month for electricity, compared to US average electric bills of about $100.
All this investment achieved only a 42% decrease in CO2 emissions for electrical generation, and only a 20% decrease of total CO2 emissions for electrical generation plus automobile use.
Full conversion to wind and solar energy cannot be done without electric grid collapse during periods when sun does not shine and the wind does not blow.
Hospitals, traffic lights, computer systems, and manufacturing plants need continuous, reliable electric power.