Hello,
In your scenario, SAM will only use the GCR input to calculate acres of land shown on the System Costs page. As long as the two $/acre cost categories are zero, the GCR will have no impact on the results for a system with horizontal photovoltaic arrays. (If you want to account for land cost, you can use one of the $/Wdc or $ units for the land-related costs.)
In the next software update, we will remove the upper limit on the GCR input so that you can specify a GCR of 1.
Best regards,
Paul.