If you are looking for a simple approach to solar water heating, a passive or “batch” system is probably preferable to an active solar water heater. Passive systems use the properties of thermodynamics to circulate the water through the system. When water warms up, it naturally moves towards colder areas, which creates a natural circulation within the system.

Though effective in warm climates, passive systems generally offer less hot water than active systems and are more vulnerable to freezing. In looking at a number of models, our expert took a close look at the ProgressivTube PT-40. Here is his review:

ProgressivTube PT-40
ProgressivTube® passive solar hot water heaters are self-contained, single unit systems that integrate the solar collector and storage tank. In most applications, this model functions as a pre-heater to an instantaneous or conventional water heater.

Because ProgressivTube® uses only local water pressure and solar radiation to operate, no pumps, controls, mechanical or electrical components are required. This lack of moving parts greatly reduces the amount of maintenance and extends the life of the system. The PT-40 system includes a bypass valve and drain tap to allow home owners to evacuate the collector of water in case of hard freezes.

Once installed, the system will work automatically. Water is circulated to the collector where it is store until hot water is used in the home. Once there is a call for hot water, the solar pre-heated water is drawn into the conventional water heater, reducing electrical or gas usage for water heating.

The ProgressivTube PT-40 solar water heater retails for less than $1,800 as a complete system. According to the manufacturer, it may reduce annual hot water heating costs by from 50 to 90 percent.