There was indeed a lot of hot air in sustainability thoughts in 2008, and probably still is, but Mackay's treatment is sometimes bordering the absurd.

For instance, the chapter on wind power starts by comparing a back of the envelope calculation on wind power with energy usage by a fossil car.

While there are occasional good points, I would not recommend reading this book unless you actually know something about the things the book is discussing. It's simply too misleading in important places.

In case anyone is wondering about this, there are real studies on the feasibility of 100% renewables by organizations that actually know this stuff and have done the modelling work.