This study presents an analysis of the energy curtailment caused by the DC series-parallel collection systems of HVDC connected offshore wind farms. Wind speed differences between the series connected wind turbines cause unequal voltages at the DC output of the wind turbines. This can lead to unacceptable over-voltage or under-voltage conditions. The over-voltage and under-voltage conditions on the turbine DC outputs can be avoided by curtailing the power outputs of the wind turbines, which will result in loss of wind power. The annual energy curtailment due to the over-voltage limits of turbine DC-DC converters is analysed for a 200 MW DC series-parallel wind farm. The impact of wake effects on the energy curtailment losses is quantified and demonstrated with a case study.