HOMER Grid 1.9

The generator derating factor is the maximum output of a cofired generator operating at the minimum fossil fraction, as a percentage of its rated output. For example, a 20-kW diesel generator is modified to run on a mixture of diesel fuel and biogas, with a minimum of 20% diesel. If the output of the engine is limited to 15 kW when operating at 20% diesel, the derating factor is 15 kW divided by 20 kW, or 75%.

Note that HOMER assumes a cofired generator can produce up to 100% of its rated output if the fossil fraction is high enough. In the example above, the generator can produce up to 20 kW, but the diesel fraction must exceed 20% for output power above 15 kW.

For a more complete explanation of a cofired generator, see the Operation of a Cofired Generator section of the help.