OG10 CR NO153翻译

153.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.

谁能帮忙翻译下蓝体字的部分，意思没看懂，尤其是“threshold of economic viability"还有括号里面一部分。

谢谢。

Thanks,jbyupei~~~

"the price per barrel to which oil would have to rise"...这一部分怎么翻译，

为了使太阳能工厂更经济，每桶油油价上升？不太理解这里是什么逻辑。

to which 以及后面的都是 price 的定语成分，   

一个价格， 什么价格呢， 为了使。。。更经济每桶油需要上升到的价格