Efficiency as a concept requires a lot of context. In this case, when the power source is free and unlimited (at least until you get close to utilizing all inco

Efficiency as a concept requires a lot of context. In this case, when the power source is free and unlimited (at least until you get close to utilizing all incoming solar energy), talking about efficiency as simply the output energy divided by the input solar energy is probably not the most useful concept. Another common example is electric heat versus geothermal heat pumps. Electric heat is "100% efficient" in the sense that essentially all the electric energy is converted into heat. And yet, a GHP can provide the same amount of heating using less electric energy, because it's moving heat from an effectively free and unlimited source.