Comment: 15 pages, 2 figuresGrowth theory has rarely considered energy despite its invisible hand in all physical systems. We develop a theoretical framework that places energy transfers at centerstage of growth theory based on two principles: (1) goods are material rearrangements and (2) such rearrangements are done by energy transferred by prime movers (e.g. workers, engines). We derive the implications of these principles for an autarkic agent that maximizes utility subject to an energy budget constraint and maximizes energy surplus to relax such constraint. The solution to these problems shows that growth is driven by positive marginal energy surplus of energy goods (e.g. rice, oil), yet materializes through prime mover accumulation. This perspective brings under one framework several results from previous attempts to insert energy within growth theory, reconciles economics with natural sciences, and provides a basis for a general reinterpretation of economics and growth as the interplay between human desires and thermodynamic processes.