Ideally with an over penetration of renewable energy (more supply than demand), electrolysis would be a perfect variable load tool to match times when there is too much wind and not enough load. Instead of curtailing the power output of the wind farms, crank up the load from the electrolysis systems and produce hydrogen.
Basically, you are describing energy storage. Using hydrogen for this purpose has several drawbacks. Namely the efficiency of the system and the storage problems that you have with hydrogen.
Under the ideal circumstance, you would use renewble energy 100% of the time and reduce the coal/nuclear sources when energy demands are low, not the other way around. If you want to see a interesting excercise in energy storage and the economics of the electrical grid, take a look at the following link:
http://www.deseretnews.com/article/1,5143,695272137,00.html