Is there any chance of being able to use Hydrogen as a heating fuel directly, ie in an instantaeneous water heater or similar?  We have a heating value for it resumably and it should be easy enough to plug into being able to use it in the boiler operation mimicking the instant water heater for a thermal load.

Good question about fueling the boiler with stored hydrogen.  That would be easy to do if HOMER could cleverly dispatch heat sources to serve the thermal load the way it does the electric load.  Unfortunately it can't do that.  What it does is much less clever.  It considers the value of waste heat when choosing among electrical power sources, but it doesn't worry about actually meeting the thermal load.  It assumes the boiler is always available to serve whatever thermal load is not met through heat recovery and excess renewable power -- unmet thermal load is impossible.  That avoids considerable complication in the simulation logic, but it means the boiler can't be allowed to run out of fuel, hence it can't burn stored hydrogen, biogas, or any fuel with limited consumption. 

Some day we will make the logic smarter to allow HOMER to dispatch components to meet the thermal load.  We'll promote the boiler to be a real component, with a capacity and a cost, so that HOMER can decide whether it wants the boiler, or how big it should be.  And you'll be able to fuel it with hydrogen.  But it's not possible right now.