Thermal lensing is becoming recognized as one of the dominant obstacles to the second generation of laser interferometric gravitational wave detectors. Very high optical power is required to circulate in the interferometer to reach the sensitivity goal, creating strong thermal induced wavefront distortion. These effects will be studied at the High Optical Power Test Facility in Gingin, Western Australia. In this paper, we present simulation results for the first test planned for the middle of 2004. This experiment will produce 5 kW of optical power circulating inside a Fabry-Perot cavity and will demonstrate large thermal lensing effects.Two compensation methods were investigated to offset the negative effect of thermal lensing on the cavity: a compensation plate within the arm cavity and adaptive laser mode matching. Advantages and disadvantages of both systems are discussed.