As can be seen from this example, the Pi, P2 method is quick and easy to carry out manually.
As also can be seen, Eqs. (12.32) and(12.34) include only PwF values and ratios of payments to initial investment of the system and do not include as inputs the collector area and solar fraction. Therefore, as Pi and Pr are independent of Ac and F, systems in which the primary design variable is the collector area, Ac, can be optimized using Eq. (12.31). This is analyzed in the following Section.