[George]

With the most efficient electrolyzer technology available, what is the volume of hydrogen produced per watt hour? I can't seem to get a straight answer to this.

[Borek]

P=UI, you have to assume what voltage is required, that will allow you to calculate current. You already know the time (1 hour), once you will know the current you can easily calculate charge. Charge and Faraday constant (mole of electrons, usually expressed in coulombs) gives number of moles. That's all.