In HOMER Grid, there are two ways of adding a generator:
(1) Expand the Components Tab and select "Generator" (column on the left in the below screenshot)
(2) Expand the CHP Tab and select "Generator (CHP)" (column on the right in the below screenshot)
The Generator (CHP) menu only lists generators that have a default heat recovery ratio of greater than 0%.
To learn more about the generator in HOMER Grid, please refer this article