Actually I am working on a wind/diesel project and I have rebuilt the system with the HOMER simulation tool.  The actual simulation step time is 10 minute.  The number of the diesel starts seems to be too high but unfortunately I have no data of the number of starts in the real system.   The number of starts is getting less in the case of a simulation with one hour steps and in the case of another diesel generator min load, say 6%. Also in case of a generator which is forced on the whole year the number of starts is getting less.  Do you have other ideas to get the number of diesel starts down?

 *This response applies to HOMER Legacy only. In HOMER Pro, you can set the minimum runtime on any generator.*

The number of diesel starts is higher in the HOMER simulation than it would be in the real system.  With this many diesels to chose from, HOMER can precisely optimize the combination of diesels that need to operate in each time step, to provide the required power and spinning reserve at minimum operating cost.  HOMER is happy to run a diesel for ten minutes, then shut it off in favour of another diesel when conditions change slightly in the next time step.  But in real life, you would not run a generator for such a short period before shutting it off.

Unfortunately, HOMER does not allow you to specify a minimum run time for diesels.  I think a minimum run time restriction would solve this problem quite effectively.

The good news is that I don't think such a restriction would significantly affect the operating cost or the diesel fuel consumption in this case.  In other words, I don't think HOMER's over-optimization of the system dispatch has much effect on the output variables that matter: fuel consumption, generator operating hours, operating costs.  That's because your diesels are very similar to one another.

For example, HOMER may decide to run two 810 kW diesels in one time step, then one 810 kW and one 600 kW diesel in the next time step, then back to two 810 kW diesels in the next time step.  In reality, you would operate two 810 kW diesels for all three time steps, but the difference in fuel consumption and operating cost would be modest.  So while it would be nice for HOMER to report a more realistic number of diesel starts, I think its estimate of fuel consumption and diesel operating hours are fairly dependable in this case.