Hydrogen obtained from water electrolysis in addition to being sustainable becomes commercially competitive when a high degree of purity is sought. Ideally such purity is achieved by keeping the electrolyzer on a constant and rated power. To satisfy this objective the assistance of the electric grid to deal with the variability of the wind resource was proposed. The disadvantage of this alternative is the failure to ensure a 100% carbon-emission-free hydrogen. The surplus wind energy can be delivered to the grid to optimize the trade-off between purity and cleaning degree. This paper presents a study on how the electrolyzer should be sized - according to the turbine and wind resource - to fully compensate these emissions along the year, that is, to cancel the annual power supplied by the grid.