<p>Turbulent convection is generally believed to occur on the Sun on three different characteristic length scales. These are the smaller granulation scale, the intermediate supergranulation scale, and the potentially existing giant cell scale. While granulation is mostly understood, there are several competing theories for the emergence of supergranules as a characteristic length scale and coherent phenomenon. While the prevailing approaches assume a convective origin of supergranulation, others follow the path of a potential wave-like behaviour of these features, because the power spectrum of supergranulation seemingly follows a dispersion relation. Since supergranulation shows an asymmetry in up and downflows, it is clear that non-linear affects must play a role in its evolution, which create a characteristic observed skewness in the divergence of the horizontal motions at the solar surface. Supergranulation may thus as well be a non-linear wave or an example of wave turbulence. While the power spectrum of supergranulation is reasonably constrained by observations, we here present an observational characterization of the non-linearities involved in creating supergranules. We characterize the spatial pattern of solar supergranulation using a third-order correlation in Fourier space, the bispectrum. We find that the strongest non-linearity is present when the three coupling wave vectors are all at the supergranular scale. These are the same wave vectors that are present in regular hexagons, which have been used in analytical studies of solar convection. At these Fourier components, the bispectrum is positive, consistent with the positive skewness in the data and consistent with supergranules preferentially consisting of outflows surrounded by a network of inflows. We use the bispectral estimates to generate synthetic divergence maps that are very similar to the data. Using this method, we estimate the fraction of the variance in the divergence maps from the nonlinear component to be of the order of 4&#8211;6%. We conclude by discussing the implications of our study on the question whether supergranulation is rather a convective feature or an example of wave turbulence.</p>