Surrogate models are used to approximate the expensive ‘true’ simulation codes and thus have the potential to speed up the wind farm layout optimisation problem (WFLOP). One technique to make surrogate models is Polynomial Chaos Expansion (PCE). PCE can approximate a (wind farm) model by using orthogonal polynomials which are constructed based on input variables. In case of a wind farm model, these are wind speed and wind direction. The technique sounds promising, but up till now, PCE has mainly been used as an uncertainty quantification method and not as much in order to help with optimisation problems. This thesis research project aims to implement the PCE method in WFLOP by implementing a multivariate polynomial basis based on the wind speed and wind direction. The usability of the method will be determined based on a comparison between the WFLOP results of the PCE surrogate model and the conventional approach.