# How can I express parameters of a natural gas generator in terms of a diesel generator?

I am using the REOpt tool from the U.S. National Renewable Energy Lab to help in sizing a new battery energy storage system and solar PV array for an existing building. The building already has a natural gas-fueled generator, and the cost to operate this should be accounted for in the optimization. Further, the site has emissions reduction targets, so the emissions from this generator need to be modeled.

The problem is, REOpt assumes that any generator is diesel fueled. How can I express these parameters of a natural gas generator in equivalent terms for a diesel generator in order to correctly run the model? Is it as simple as multiplying everything by the conversion factor for gallons to therms, or will it be more complicated?

Input Diesel units (input) Natural gas units (known)
Fuel cost dollar/gal dollar/therm
Fuel burn rate gallons/kWh therms/kWh
Fuel consumption curve y-intercept gallons/hour therms/hour
Generator fuel emissions factors (CO$$_2$$, NOx, SO$$_2$$, and PM2.5) lb/gal lb/therm

To enable generator input parameters you first need to select "Resilience" as a goal, then "Generator" as a technology. Select "Advanced inputs" to see additional parameters. Emissions rates are in the "Renewable Energy & Emissions" section under "Advanced inputs."

• A therm is ,more or less , 100 cubic feet of methane at STP. Jan 30 at 22:15

I think you need to do this on an energy equivalent basis.

Firstly determine the amount of heat energy, in joules or BTU, that can effectively be provided by one gallon of diesel. Similarly do the same for a therm of gas. This will then give the number of therms of gas that can provide the same heating effect as one gallon of diesel. That should suffice for the first three items on the list.

The last item of the list, fuel emissions, will be different because gas tends to have fewer polluting contaminants compared to diesel. Less CO2 will be produced, likewise for NOx, SO2 and PM2.5. You would need to get those figures, possibly from the fuel suppliers.

• Yes, this is what I ended up doing, using the heat content of each fuel in terms of BTU (which was most readily available). Later this month I'll be writing up my report for the project so if I remember I'll come back and post my findings as an answer. May 31 at 18:15

I would compare the gallons of diesel to therms of gas and that would be the key to sorting yhe input values.

You need to find the reliable sources of info for the two fuels you are comparing - even diesel is not the same summer to winter and neither is gas.

Found 1 link but you need to decide if others are better:

https://www.kclarson.com/Compare-Fuel-Costs.php