It is easy to get solar resource data into HOMER via the Internet
In the Solar Resource Inputs window, enter your latitude and longitude, then click Get Data Via Internet. If you are connected to the Internet, that button retrieves monthly solar data for the specified latitude and longitude from NREL's and NASA's satellite databases. Give that a try, it's really handy. (If you specify a lat/long outside the US, HOMER refers to the NASA SSE dataset. So depending on what location you request data for, HOMER might ask you to specify a username for NASA on their SSE website.
Please use firstname.lastname@example.org as your NASA SSE username in HOMER2. NASA recently re-configured their website and eliminated the need to validate specific email addresses. To enter this in the HOMER software, open HOMER2, select File >> Preferences, and enter email@example.com into the field for NASA SSE username.