Triboelectric nanogenerators, or TENGs, are prominent among power take off (PTO) systems being researched for use in specifically small scale wave energy converters (WECs). The low power requirements, and modest size of data buoys, suggests TENGs as an ideal PTO for this small-scale wave energy application. However, a physics-based model of the relationship between the movement of the buoy and the performance of the onboard TENG is difficult, particularly for rolling-ball-type TENGs. This paper develops three multiple input single output system identification (SI), black-box models for a rolling-ball-type TENG. The SI models are identified, and validated, using input-output data gathered from real wave tank tests on a 1:8 Froude-scaled model of a navigation buoy. The models described in this paper, relate the TENG’s current output to the displacement, in 6 degrees of freedom (DoFs), of the buoy to which it is mounted, across a range of wave conditions. The SI models used include linear autoregressive with exogenous input (ARX), and nonlinear Kolmogorov-Gabor polynomial (KGP).