Thank you for this message! Yes, you may still include PV & DG as part of the existing DER setup. Just ensure the CAPEX cost is zero, since its already paid for and include other costs like O&M. On your second point, the cost of fuel for an ICE generator is controlled in the GUI by 2 parameters: fuel cost (in $/gallon) and Efficiency (gallons/kWh). To have the GUI consider natural gas as a fuel, you must adjust these 2 parameters accordingly (even though the units may be improper). Note that in the next release of the GUI (coming soon), DER-VET will have a newly designed project-wide fuel cost with units in MMBtu instead of gallons.