Bitcoin Q&A: Energy consumption
Basically since most energy produced is usually lost( due to the fact energy can't be stored efficiently or storing energy costs more than making more energy itself ) bitcoin mining gives another use for this energy preventing it from being wasted and giving it value. It also will force miners to use renewable resource because nonrenewable resource will keep on getting expensive. In fact here are already solar bitcoin farms. Yes not the best but the stats saying bitcoin mining is completely wasteful is not true.