Power systems are facing complex challenges in order to achieve environmental targets, such as a strong abatement of CO2 emissions. Hence, an increasing share of renewable energy sources (RES) will change the generation portfolio. This is likely to push network operation into a risky territory, due to a lack of system inertia. This paper quantifies the impact of providing `effective inertia' by controlling domestic thermostatic loads. This inertial support mechanism would permit full absorption of available wind power even for those scenarios characterized by low demand and high wind penetration.