HOMER uses the following equation to calculate the levelized cost of hydrogen:
Where Cann,tot is the total annualized cost, velec is the value of electricity (you enter that in the Hydrogen Load Inputs window), Eprim is the primary electrical load, Edef is the deferrable load, Egrid,sales is the total energy sold to the grid, and Mhydrogen is the total hydrogen production.
In the numerator, we are trying to establish the annualized cost of producing hydrogen by subtracting the annualized cost of producing electricity. If your system meets no electric load and exports no electricity to the grid, then that whole electrical term will reduce to zero.