A pressurized solar hot water system almost always follows a standard layout, which is one of the reasons most manufacturers are able to offer simplified kits for residential installations.

Pressurized systems normally use flat-plate or evacuated-tube collectors to heat a solar fluid made of propylene glycol and water. The collector array is connected to the heat exchanger by two insulated copper tubes which are completely filled with solar fluid and are sealed closed.

The pipe that brings solar fluid to the collector has a small pump attached to circulate the fluid. An expansion tank is also installed on this pipe, along with valves to drain and fill the system, a check valve and a pressure gauge to monitor performance. A pressure-relief valve and associated drain pipe are installed in case the solar fluid gets too hot.

The other half of the loop takes the solar fluid back to the heat exchanger after it has been heated in the collector array, and usually has a temperature gauge, a pressure gauge and a combined temperature/pressure relief valve installed on it.

The power for the system is often provided by a PV panel which generates the electricity needed to run a small DC pump , with or without a controller attached. Alternatively, a differential temperature controller can be installed with a 120V AC pump.

When the collectors are heated by the sun, the controller starts the system: solar fluid is pumped around the closed loop, carrying heat from the collector array back to the heat exchanger. There, it passes the heat to the domestic supply before returning to the collector and being heated again.

When the pump stops operating, the solar fluid lies idle. Since the pipe loop is closed and filled, there is always solar fluid throughout this part of the system, in the pipes and collector(s), which not only carries whatever heat is generated by the sun's radiation but protects the system from the effects of freezing external temperatures.