You mentioned you would like to model thermophotovoltaic generators but cannot with HOMER.  In fact, HOMER is capable of modeling a TPV generator that burns fuel.  If the TPV generator operates off waste heat from some industrial process, it might be difficult to model it in HOMER.  But if the generator consumes fuel to produce electricity, it is just like an internal combustion engine generator, microturbine, fuel cell, thermoelectric generator, or stirling engine in that it consumes fuel at some efficiency to produce electricity and possibly heat.  The efficiency can vary according to the electrical output, although HOMER can't model a generator that gets less efficient at higher output.