This paper investigates the marginal system value of increasing the penetration level of wind power, and how this value is dependent upon the specific power (the ratio of the rated power to the swept area). The marginal system value measures the economic value of increasing the wind power capacity. Green-field power system scenarios, with minimised dispatch and investment costs, are modelled for Year 2050 for four regions in Europe that have different conditions for renewable electricity generation. The results show a high marginal system value of wind turbines at low penetration levels in all four regions and for the three specific powers investigated. The cost-optimal wind power penetration levels are up to 40% in low-wind-speed regions, and up to 80% in high-wind speed regions. The results also show that both favourable solar conditions and access to hydropower benefit the marginal system value of wind turbines. Furthermore, the profile value, which measures how valuable a wind turbine generation profile is to the electricity system, increases in line with a reduction in the specific power for wind power penetration levels of >10%. The profile value shows that the specific power becomes more important as the wind power penetration level increases. (C) 2017 Elsevier Ltd. All rights reserved.