That's not what he means. A solar energy harvester with 0.1% efficiency might still be worth it if the costs are low, it doesn't matter that you "wasted" the other 99.9% since it's unlimited.
It does matter when it comes to CO2 fixation though... if you only get 0.1% efficiency in fixing CO2 with biofuel production, but would get 1% with normal forestation, then there is a quantifiable difference.
