Roma Valve converts any standard water heater tank to a solar water heater (storage) tank.  It replaces the tank's drain valve. Cold water is  removed from the bottom of the tank and discharged back to the middle of the tank through solar loop. The flow rate can be adjust for an optimal operation. 

Roma valve converts any tank to a solar tank.

The Roma Valve consists of two coaxial pipes and one balancing valve. The inner pipe discharges warm water into the storage tank, while the surrounding outer pipe takes the cold water from the tank. A circulating pump, in concert with the Roma’s balancing feature, circulates water (or heat transfer fluid through a heat exchanger) in the solar loop as shown: