A solar collector assembly comprises a plurality of heater collection tubes. A thermal enhancement manifold assembly is integrated into the solar collector assembly to enhance thermal efficiency. The enhancement manifold assembly includes a supply manifold subassembly which selectively distributes a refrigerant between at least two supply manifolds and a return manifold subassembly which distributes the refrigerant between at least two return manifolds. A thermal enhancing tube provides fluid communication between each supply manifold and respective return manifold. The thermal enhancing tubes are assembled within an interior volume of the solar heater collection tubes. Each manifold pairing is operatively governed by a respective fluid control valve. The manifold pairings alternate between an active state and an inactive state, optimizing thermal transfer between the collection tube and a refrigerant. The refrigerant is retained within an inactive tube set of thermal enhancing tubes and flows therethrough in an active tube set.