What Is a Solar Controller?

In terms of solar hot water systems, a solar controller is the component that controls the pump that moves the heating liquid through the collector. Solar controllers differ in sophistication and functionality but all include at least two temperature sensing ports and one output port which drives the pump. More complex controllers may include additional electronic features which improve the efficiency of the system or digital readouts which display important system information. Depending on the range of functions included, a solar controller may be included in the heating system itself or in a remote, user accessible location.

Solar water heating is growing steadily in popularity across the world on the back of spiraling energy costs. These systems generally consist of a collector and a water tank. Water, or a specially formulated heat transfer fluid (HTF), is exposed to solar radiation through the large surface area of the collector. The heated fluid is then circulated in several ways to the water tank where it transfers heat to the tank contents. Obviously this movement of fluid between the collector and water tank is crucial to the efficient operation of the hot water system but also serves as a safety measure to ensure the collector does not overheat at times of low demand.

In active solar hot water systems, this movement of fluid is achieved with an electric pump run by a solar controller. The controller features several temperature sensing ports which gather data from temperature probes located at various points in the system, particularly the collector and tank. When fluid circulation is required, the controller will send a signal via an output port to activate a relay which in turn switches on the pump. When the system temperatures reach the point where circulation is no longer required, the controller cuts power to the relay, switching the pump off again.

This basic functionality may be achieved with very simple electronic circuits which are often built into the collector or motor housings. Many solar controller units feature additional functionality, however, in the form of additional sensors and controls to prevent energy wastage due to pump short-cycling. This level of control is usually achieved by including microprocessors in the controller circuit. This type of controller is generally located where it is easy to access and often includes a digital display which can supply essential system information. Many solar controller models also include override controls to manually start and stop the pump.