Why are you giving an option of hydrogen load instead of a hydrogen fuel cell?

HOMER models hydrogen fuel cells.  The hydrogen load is entirely different from a fuel cell.  Use a hydrogen load only if you want to simulate a system that produces hydrogen for some external use.  To simulate a system that electrolyzes excess electricity to produce hydrogen, stores that hydrogen in a tank, and then uses the hydrogen to supply a fuel cell, you do not need a hydrogen load.  At least one sample file on the HOMER website demonstrates how to model a fuel cell in this way.

The efficiency of the electrolyzer is based in the higher heating value of the hydrogen, but if I want to model a fuel cell, the stored hydrogen is based on the Lower heating value.  Why is that?

We chose to specify the energy content of all fuels using LHV because we think that is the most common metric.  But we found that electrolyzer manufacturers tend to specify efficiency in terms of HHV, so we used HHV for the electrolyzer efficiency.