Unless your property is on the same parcel of land as the solar farm and receives electricity directly from the solar farm (i.e. the electricity does not pass through the grid), you should enter this energy under a grid electricity meter. You’ll want to track solar farm electricity on a separate meter from the property’s non-solar grid electricity. You’ll then mark that electricity as Green Power (assuming you have retained the RECs). The reason you’ll use this approach is that solar farm electricity that passes through the grid is still subject to losses in transmission and distribution, which impact the property’s source energy and source EUI.
You will be asked to enter the quantity, fuel source (100% solar), and the generation location. While you probably know the location of the solar farm, Portfolio Manager may not, so you will probably have to select the eGRID Region from the list.
The first option under "Generation Location," ("I know the specific plant where the energy was generated") will only list power plants with a nameplate capacity of 1 MW and above, and it will take ~3 years from the time a new plant switches on to the time it shows up in this list.