Hi Joe,
In Excel Exchange, the "Send To" variables are for SAM input values that you might want to use in an Excel Formula to calculate another value. For a simplistic example, for a PV system, you could use Excel Exchange to calculate an annual O&M cost that scales with the number of inverters by defining the Number of Inverters variable as a Send To variable to send its value to a cell in the workbook, and then use a different cell in the workbook to store a formula that converts number of inverters to an annual dollar amount, and defining the Fixed Annual O&M Cost as a "Captured From" variable that reads the value from that cell. When you run SAM, the temporary copy of the workbook would make the calculation and exchange the values with SAM.
Best regards,
Paul.