His solar calculations IIRC were off by a factor of 10 in terms of what amount of energy could be extracted from a given piece of land. I do not have the book now otherwise I could've pointed it out. I think he was calculating the footprint of different forms of energy. Thumb rule is that at 20% efficiency a PV panel can get 200 Wp energy per sq m which translates to 200 MW per sq km. Leaving aside space for equipment, gaps, roads etc one can easily have a thumb rule of 100 Mw peak per sq km. I believe his book had this calculation as 10-20 MW per sq km.
This assumes 1 KW peak irradiance. Off course things will change based on latitude, season etc and one has to adjust for these factors however Solar is a no brainer in tropical and temperate climates alike at this point in my opinion.
