There are two templates of generators in Homer Grid:
(1) Fixed Size - A generator that uses the "Fixed Size" template will not have a search space.
(2) Size your own - A generator that uses the "Size Your Own" template will include a search space.
When you are adding a generator to your model, you can differentiate the two templates by the name as shown below:
If you chose a Size your own generator, then you can see the Search space section allowing you to enter multiple generator sizes.
When you select this template in the library, and are ready to create a size your own generator, make sure to un-check the " Fixed generator Capacity".