We do improve our energy efficiency. For example, combined cycle gas generators are 60% efficient, about twice a good as nuclear reactors. So, in the absence of cogen, 40% of the heat is discarded. But, so it the other 60%. Turning on a light heat the wall the light shines on..... So, it is 100% waste heat eventually. It is the 100% stuff (after use) that must be emitted to space and that is what the paper proposes to search for.