lost in space

Imagine you’re lost in space, with no energy source in sight, only the CMB: Could you use that as an energy source? clearly not the CMB-monopole, because of thermal equilibrium, but by using the anisotropies? What conversion efficiency would you be able to get?

Patches of different temperature in the CMB can be used as an energy source and the energy conversion would depend on the Carnot-efficiency \(1-T_c/T_h\). With typical variations of \(\delta = 10^{-5\ldots -6}\) between hot and cold patches, one obtains \(T = T_\mathrm{CMB}(1\pm\delta)\) and \(\eta \simeq 2\delta - \delta^2\), so similar numbers for \(\eta\) and \(\delta\).