District heating with renewable energy. Baseline?

I'm modeling a district heating system according to option 2 of “Treatment of District or Campus Thermal Energy in LEED V2 and LEED 2009 – Design & Construction”. In the proposed model I'm going to model a virtual on-site hot water boiler, according to Table 4 of the document. Since the real district heating is fueled by agricultural crops, I can consider it as renewable energy (see page 15 of “Treatment of District or Campus Thermal Energy in LEED V2 and LEED 2009 – Design & Construction”). For the baseline model I have to consider System 7 (according to Table G3.1.1A of ASHRAE 90.1). What fuel shall I consider in the baseline model? Since in the real plant there is a system (another district system) that is fueled by natural gas and that can be considered a backup system, shall I model natural gas for the baseline model? The use of natural gas is very common in Italy (I would say, it's the “standard solution”). Best Regards