When optimizing a generation design using HOMER, sometimes the size of component in the generation design shows up as "Not Included." This means that HOMER has determined the optimal, lowest cost system (given your load, location and cost parameters) does not include that generation component.
This often happens with the Generator component.
HOMER may exclude a generator if there is a "Minimum Renewables Fraction" constraint. This constraint acts as a filter. HOMER will first run the algorithm to determine the lowest cost system (which includes determining first the optimal run time for the generator), and then remove any systems that do not meet your renewables constraint. Therefore, if you have a relatively low fuel and O&M price for your generator, the lowest cost system may include a generator that runs more often than the minimum threshold you have set. HOMER will discard this result, and provide only the result that does not include the generator (to meet the constraint).
The best way to address this is to increase your fuel and O&M costs to limit HOMER's generator run time. Make sure to include replacement costs for the generator as well, to fully reflect the asset's lifetime costs. You may also want to increase your Load Availability constraint so that the generator is more likely to be used to meet the most expensive hours of production.
You may also switch off Optimize for the generator component and manually include a generator. However, if HOMER would determines the lowest cost option is to run that generator for longer than your renewables constraint allows, you will receive a notification that HOMER has determined that the design is not feasible. Increasing your generator costs will reduce the run time of the generator.
To return a size for the component from the optimization, try lowering the unit cost of the component or relaxing input constraints. See also:
Iterating with Optimizations