In 1979, Nicholas Georgescu-Roegen famously wrote: "matter matters, too". In this way, he emphasized the material foundations of economic activities, and criticized the theories of production whereby materiality was out of scope. In his view, this shortcoming was due to a quantitative (or "arithmomorphic") bias that prevented most economists to take into account the qualitative characteristics of the world. In this paper, I look deeper into Georgescu-Roegen's diagnosis by examining other reasons for this shortcoming (atemporality, homogenization). Because of its various material forms, energy is a typical case: the economists have always felt some discomfort with it. I illustrate this discomfort with two examples in the history of economic thought. And back to Georgescu-Roegen's fund-flow proposal to overcome the common difficulties, I suggest that the next transition to renewable energies, which have peculiar material specifications, might challenge the economics of production both in its standard and in its roegenian shapes.