When trying to choose the best solar hot water system for your needs, the first thing you want to decide is whether to install an active or passive system. A passive system uses the principle that warm water rises as cool water sinks to circulate hot water through the system; an active system pushes water with the help of a pump.

An active system requires a little more equipment--some kind of circulating pump and a few other components--because of this, it is generally more expensive and has more potential for things to go wrong. It requires electricity to run the pump, so it is less energy efficient. 

On the flip side, it can provide abundant, continual hot water because the pump circulates the water through the system.

Solar water heaters are comprised of three basic components: collector, tank, and circulation system. Of the three components, the collector has the greatest impact on the efficacy of your water heater as it is the part of the system that collects the warmth from the sun and transfers it to the water. For more about the complete workings of solar water heaters, please see How a Solar Water Heater Works.

Reviews: Passive Solar Water Heaters

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.

Reviews: Active Solar Water Heaters

If you live in a cold climate or are looking to really get the most out of your solar water heater investment, an active system may be the way to go. Active solar water heaters force water through the system using a series of pumps and valves to maximize delivery of the sun’s energy. Two popular models are the Fafco PN760 Hot2o and SolarRoofs Skyline System 3.

Fafco PN760 Hot2o

Specifically designed for homes with electric hot water heaters, the Fafco PN760 Hot2o solar hot water heating system is the only polymer system designed for domestic hot water heating. Fafco made a name for itself by first using polymer materials for swimming pools heating systems, which have now become the industry standard material for non-domestic purposes.

While most solar heating systems employ copper tubing in the collectors to absorb and retain the sun’s energy, the Fafco system uses extruded polymer. The advantages of this sort of circulation system is that the unique self-locking connectors and flexible polymer tubing avoids sweated fittings and reduces installation time, difficulty, and leak risk. If mail ordering the system, you’ll appreciate the fact that the Fafco collectors weigh considerably less than traditional systems and are more compact.

Retailing at around $2,200, the PN760 Hot2o system has a 10-gallon capacity and includes a wall mounted drainback tank to prevent the chance of freezing and damage to the system in colder climates. The circulation pump uses a standard 120-volt electrical supply and is activated by a programmable timer to maximize solar exposure. Two roof-mounted collectors are included in the system and additional panels can be purchased for about $450 to increase effectiveness. The low-profile collectors have a 2-foot width by 12-foot length.

SolarRoofs Skyline System 3

The SolarRoofs Skyline System 3 is another active solar water heater that retails for under $1,800 and offers homeowners a complete system ready to install out of the box. The Skyline System 3 off the advantage of connecting directly to your existing hot water tank and not requiring an additional storage tank to supply your home with hot water.

Using the more traditional copper tubing to absorb the suns energy, the Skyline System 3 is an “open loop” system that directly circulates the water from your hot water tank through the collector. This type of system is much more effective in transferring the collected heat energy directly to your home’s water supply, but can be vulnerable to cold weather. In sustained freezing temperatures, water used in the system does have the potential to freeze.

Frozen pipes would not only block circulation but also pose the risk of bursting the collectors' tubing. In regions where light freezes are possible, the systems are protected two ways--they are fitted with a dribble valve that will drain the collector of all fluids as temperatures approach freezing, and they recirculate a small amount of warm water from the hot water storage tank to prevent freezing.

Another feature of the Skyline System 3 is that the package includes a photovoltaic (PV) powered circulation pump. This feature allows for the system to operate without adding any cost to your electric bill. When the sun is up, the system automatically starts circulating water.

The Skyline System 3 also includes a mixing valve to protect from high solar water temperatures, 50 feet of copper pipe to link the collectors to your hot water tank, and mounting rails for the collectors. The collectors come in two sizes, a 20-1 style that is 12 feet long by 20 inches wide, and a 10-1 style that is 6 feet long by 20 inches. Forty square feet of collector area is used most in mild areas, from California through southern states. For colder regions such as New England, Colorado and northern states, 60 square feet of collector area is recommended.