The solar water heating input Incidence angle modifier input is actually the coefficient b0 in the equation IAM = 1 – b0 × (1/cos(q) – 1). The label is misleading, but the description in Help is correct: "The incident angle modifier coefficient: The constant b0 in the equation, IAM = 1 – b0 × (1/cos(q) – 1)."

Solution is to change label to IAM coefficient.

Also Total system flow rate input does not appear to be used in the code. Consider removing the input, or explaining that it is not used in the Help description.