If a farm is unable to provide the number of gallons of propane used, how should one proceed in the evaluation?

FARM ES cannot provide estimates or industry averages for propane use because it varies tremendously. We would recommend referencing a FARM ES evaluation on a farm of somewhat similar size and style. Use that farm’s propane use as a proxy estimate.
Another option is to find out if the farm has a sense of propane use from a previous year that can be used as an estimate. Or, if the farm knows how much money they spent on propane you could use that to back-estimate the actual usage.

You could also reach out to local extension services for an idea of an estimate.

How should the question about the “percent of heating potential utilized” be answered when 60% of this heat is used to power the digester and 40% is used to heat domestic hot water and some rooms?

You should enter 40%. The 60% that is used to power the digester does not count toward the heating potential utilized. When we think about ‘heat potential’ and ‘energy potential’ used we should always think of the digester and its processes as something that can fit in an envelope. Anything we add to the envelope (electricity for example) needs to be included as an input and anything that leaves the digester unit can be included as an output. Therefore, if electricity (or heat) is created by the digester but goes back to running the digester, it should still be considered ‘in the envelope’ and therefore not included as an output. For the question at hand, only the heat used to warm the water for use in the farm can be counted as heat potential used.

What grid GHG emission factor does FARM ES use? Can a state grid number (kg CO2e/kWh) be used for a specific year instead?

FARM ES produces a lifecycle based GHG emissions estimate (cradle to farmgate). The electricity emissions factor is also lifecycle based. It is 0.842 kg CO2e / kg FPCM. This was originally derived from the ecoinvent database. We are exploring updating the electricity and energy emission factors in the future using DOE factors (e.g. those found in the GREET model). We do not recommend replacing the emissions factor with the eGRID factor since it isn’t lifecycle based.