The threshold of economic viability?

Question

Here is an English para :

Technological improvements and reduced equipment costs have made converting solar energy directly into electricity far more cost-efficient in the last decade. However, the threshold of economic viability for solar power (that is, the price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-fired power plants) is unchanged at thirty-five dollars.

i don't understand "the threshold of economic viability".

why they are saying "the price per barrel to which oil would have to rise in order for new solar power plants to be more economical " ?

what is "oil-fired power plants" ? does solar plants also consumes oil ?

Answer 1

He's saying that the moment the price of a barrel of oil rises above thirty-five dollars (the "threshold" price), electricity from a traditional oil-fired power plant becomes more expensive then electricity from solar energy. And solar power then becomes economically profitable.