Dear Nicole,
I have the following observations based on the file you emailed me:
1. You are modeling a solar field with heliostats one one side of the tower, which suggests the design is for a cavity receiver rather than the external receiver specified in SAM. To change the receiver to a cavity receiver, on the Tower and Receiver page, choose Cavity Receiver, and, because you are using your own heliostat layout, click No in the message asking about running the optimization wizard. Then, change the receiver dimensions in the Cavity Receiver box to the dimensions of your reciever.
2. In our tests with small power tower systems, the solar field characterization calculations seem to fail when the receiver design thermal power (shown as a calculated value on the Tower and Receiver page) is around 1 MWt or less. That's because the algorithms are designed for larger systems and we did not test them for smaller systems. We don't know exactly why the calculations fail, but are investigating. We can't promise a fix for this at the moment, but it is helpful for us to hear from people who want to model small tower systems to give us a sense of how many are affected by this limitation of SAM.
Best regards,
Paul.
