It has long been the basis of solar pool heat design to have an opposite end feed and return. In fact, it’s published in several books and manuals about solar pool heating. This is not the case with FAFCO brand solar pool heating panels, which can be installed with same side feed and return. The downside is greatly increased backpressure.
Opposite end feed and return simply means that the plumbing that brings up to the solar panels and connects to the lower header is connected at the opposite end of the bank of solar panels from where the plumbing connects to the return line to the pool. Conceptually, this is done to ensure that all solar panels get filled with water and the flow rate is even throughout the bank of panels.
The FAFCO system is a bit different, mainly because FAFCO’s panels have sub-header that supposedly helps to balance the flow among all panels in a solar array/bank. This ensures that all panels have the same flow rate in theory, but the added backpressure reduces the flow rate, reducing performance for a given pump.
It is important to note that you cannot exceed 12 panels in a row with same side feed and return (see Figure 4). Also, split feed and multi-bank systems with varying heights must use opposite end feed and return lines (see Figure 5). The FAFCO manual is very clear about the layouts that are permitted.