At high levels of wind penetration the requirements of dispatchable reserves and inertia limit the volume of wind that can be accepted; the surplus is then curtailed. Marginal curtailment is 3-4+ times the average curtailment, but even in an efficiently designed market, price signals for wind investment are given by average not marginal curtailment, requiring a corrective charge to restore efficiency. The paper sets out a model calibrated to Ireland in 2026, showing the sources of distortion, formulae for the subsidies and charges needed to deliver the efficient level of renewables penetration, and estimates of their magnitude.