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Solar hot water tanks

Solar hot water heater storage tanks

Solar hot water tanks are vital components of any solar powered water heater. These storage tanks make it possible for the heating system to provide hot water day or night and rain or shine.

Solar storage tanks are well insulated and provide heated domestic water to the systems' back up unit, which is usually an existing conventional tank or a tankless hot water heater.

Solar hot water tanks in passive systems

In batch solar water heater designs the storage tank is connected to the panel or collector. In batch systems' an insulated storage tank with absorber material, is covered in a glazed collector box. The tank is placed within the collection box.

In thermosyphon solar water heating systems the storage tank is integrated with the collector or panel as well. In thermosyphon designs the solar storage tank is placed directly above either a flat plate collector or an evacuated tube collector.

Solar hot water tanks in active systems

In active solar water heating systems the storage tank is separated from the collector or panel. In active designs the solar hot water storage tank is installed indoors, and in close proximity to the back up storage and back up power source.

In these systems heated fluid is circulated from the solar panels and to the solar tank. And when the hot water tap is on, the same heated water from the solar storage is diverted to the back up storage for on demand use.

In closed loop, or indirect, solar water heaters, a solar heat exchanger is required to transfer heat from a heat transfer fluid to the stored domestic water.

Solar hot water tanks with heat exchangers

Integrated solar hot water storage tanks are becoming the new wave. For closed looped or indirect water heating designs, storage tanks are being introduced that come equipped with internal heat exchangers. Since the heat exchanger is pre placed within the insulated tank, these models are designed to boost efficiency.

In fact some newer solar hot water tanks are even further integrated because there designed to serve as the system's back up source also. Currently there are three types of integrated tanks; storage only, direct back up and indirect back up.

Storage Only

Storage only solar tanks are still the most prevalent type available. Storage only models, more times than not, have one coiled solar heat exchanger immersed within the lower half of the insulated storage tank.

In storage only solar hot water tanks the heat transfer fluid passes through the coiled heat exchanger which in return transfers heat to the stored domestic water in the tank by way of direct contact.

Direct Back Up

Direct back up storage tanks are quickly becoming the new standard in solar hot water heaters. These models have an immersed coiled solar heat exchanger along the bottom of the tank. The coiled heat exchanger is also designed for the heat transfer fluid to warm the stored domestic water.

More importantly, direct back up solar storage tanks come equipped with a built in secondary power source, usually electric but gas powered models are available. The built in secondary heating element, more times than not, is located along the top of the tank, heating only 20 to 40 gallons of water, depending on the overall storage volume, when solar radiation is unaccessible.

The secondary heating element is used only when the fluid from the panels (or collectors) fails to keep the stored water at a set desired temperature.

Systems and designs with direct back up storage tanks are commonly referred to as single tank solar water heaters, because regardless of the existing plumbing, only one storage tank is ever required.

If a single tank solar hot water heater is properly sized and installed, the built in back up heating element should only be utilized on very cloudy days, during some cold nights and when demand is unusually high.

Indirect Back Up

Indirect back up solar hot water storage tanks are the least common integrated models available. These models have one heat exchanger along the top and one along the bottom of the tank. The heat exchanger along the bottom, just as with all integrated models, is designed for the fluid to warm the stored domestic water.

The heat exchanger along the top can be used in several different ways. It can be used to provide additional heat to an existing back up water heating system or it can be used to provide a boost to a home furnace or space heating system.

Indirect back up solar hot water tanks can also be utilized to supply a boost to a solar pool heater. In some applications, the heat exchanger along the top can be plumbed to supply a recirculating plumbing loop, which in return would keep a true on demand supply of hot water at the tap.

If your considering an indirect solar hot water storage tank, especially for these plumbing applications, it would be advised to consult a local solar installer.

Storage volume

Solar hot water tanks, whether integrated or not, come in a wide range of sizes much like conventional storage tanks. With that said, it's important to note that in active solar hot water heaters, a larger storage capacity is always required.

This is especially true with integrated direct back up tanks, because system proper sizing will require at least one full day of an electric or gas powered supply.

If your system or design incorporates a conventional storage tank as a back up unit, for more energy efficiency consider installing both a water heater timer and a water heater blanket on the back up storage tank.

More on solar storage tanks

More on solar hot water heaters


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