Consider the power/power density ratio 10⁵ m² for the “zero dimensional” hydro resource in the figure in Box 36.3, compared to the “1D” waves resource (10⁷m²) and the “2D” solar resource (10⁷m)². Try to explain the relative ratio in the hydro case using the scale of a typical hydro power installation (which is very small compared to the terrestrial length scale) and a rough estimate of the number of independent hydropower installations that could be constructed.