[Solved] storage not charging if allow diesel-off operation is not active  


I am simulating a system wind+diesel+storage. The system works correctly if the option "allow diesel-off operation" is selected in the controller page.

However if I deselect this in order to avoid start-up of the generator, the storage is charged at 100% SOC and is not used anymore during the simulation.

Can someone explain me why and how to deal with this in order to balance the use of diesel generator and storage?


Hey Maurizio, check out the comment I left on your other post.

- AF

Dear Andrew thanks for the answer.

I attach a file of some experiments I did in order to better explain what happens. I think I have found a very strange behavior and if you could check it that would be great.

In any case reading the document you suggested I have found that there should be an option in system control tab that is named "fuel minimization". However this option is disappeared in my version that is a trial 3.7.6. Could you tell me something about this? Because this option could be very useful to me.


Thank you for any further help


Hello Maurizio,

Select the option "Allow diesel-off operation" if the system can maintain stability without the generator running. This option only has an effect if there is a generator in the system which can sometimes be turned off. Some systems require a generator to maintain bus voltage and frequency. If the system includes a "grid-forming" component other than the generator, you can deselect this option, and HOMER will turn the generator off if the load can be supplied with other sources. 

If you uncheck the "Allow diesel-off operation", the generator will not be turned off. Also if you have selected "Parallel with AC generator" on the Converter page, it is always going to be in sync with the generator, thus keeping the genset always on. That is why when you choose not to have the diesel-off option, your battery is stays at 100% SOC. If you want to cycle through the battery, then you will have to allow the generator to be off at times, allowing the converter to sync with the battery. 

The fuel minimization option does not exist anymore. You can do this by setting a very high fuel price in your Genset and lower component costs, forcing the dispatch to minimize the cost on fuel. You could then sort the results by the fuel usage/ price, allowing you to view results by the minimized fuel option. 

Hope this helps!

- Aarabi Madhavan 

Hello Aarabi,

thank you for your kind clarifications. If you have still time to consider my issue I write down here some comments.

Thank you in advance

1. Fuel minimization option would be very useful. Forcing the price of fuel high is an uncomfortable workaround because Homer is useful at calculating prices and expenses, so if I put in wrong numbers...

2. It is quite strange that Homer does not take into account the number of start/stop of a genset as it strongly affects the life of the component (it is not feasible to have 17,000 start/stop in one year!).

3. If you could read my document I think there is a BUG in the optimization strategy of Homer. I copy here what I mean:

being the battery charged by the genset at the beginning of the time series, due to lack of wind energy, the “cost of cycle charging” is obviously at least equal to the cost of the fuel consumed to charge the battery. This will prevent for any future time sample the battery to be discharged! But this should not be the case as there are many time samples where there is excess energy due to renewables and therefore the cost of cycle charging would be zero. And I wonder also: if at any time it happens that the battery is charged by the genset unless by the renewable, it will be discharged no more!


Hello Maurizio,

There is an option called Minimum Run time, in which you can specify the minimum number of minutes a generator has to run if started. 

As I explained in my previous reply, if you want the battery to cycle through you will have to check the "allow diesel-off option". 

- Aarabi Madhavan 

Hello Aarabi,

thank you for your support. I used the minimum run time option and it helps in reducing the number of stops of the generator. However the issue is twofold:

1. As outlined in my previous comment at point 3, it seems that HOMER has a bug when operating with the option allow diesel-off deselected. Would you check if my statement is correct?

2. It would be advisable that HOMER includes also the start and stop of diesel generators in the optimization algorithms because this affects the life of the system and therefore the cost and therefore it could be more convenient to discharge the battery rather than stop the generator.

Kind regards



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