Wind energy predictions accounting for both clumping and porosity of the clumping stratification in which clumping sets in at the sonic velocity (models labeled 2) and at 0.4 3_∞ (models labeled 3). The scale of the clumps is given by H_ρ/D, where D = 10,100,1000. These results should be compared to the corresponding models in Fig. 4, which account for clumping but not for porosity. The addition of porosity always causes a decrease in E_kin. See Sect. 3.2 for a discussion.