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Solar hot water pump

Solar hot water heater pumps

A solar hot water pump is an essential component of an active solar water heater. Water pumps are the moving components that circulate either the domestic water or the heat transfer fluid throughout the solar powered water heating system.

Quality solar water pumps (also referred to as water circulators) should effectively and efficiently distribute fluid for several years without fail. When choosing a pump for a solar hot water heater, there are three major considerations to make; the materials used, the pump head and fluid flow rate and the pumps' power source.

Components of a solar hot water pump

These hot water circulators are essentially made up of three internal components; the motor, the impeller and the impeller housing.

Pump Motor

The water pump motor is either AC powered or DC powered, and these pumps are activated by either a differential thermostat control or a PV module.

Pump Impeller

The solar pump impeller functions much like a circulating fan. The pump motor, once activated, spins the impeller and the impeller in return thrust the fluid in the loop forward and through the pump housing unit.

Impeller Housing

The solar water pumps' impeller housing is simply the area where the fluid enters before it's circulated through the water heaters' pipes or solar loop.

Materials used

The material the solar hot water pump is made of can very well determine how long it will last. Many inexpensive solar hot water pumps are made out of cast iron, and rust is the biggest long term enemy of cast iron.

It's important to note that in open loop or indirect solar water heater designs, using a water pump with a cast iron impeller housing unit is not advised. Oxygen breeds rust and in open loop systems, oxygen is constantly introduced throughout the solar loop.

Solar hot water pumps with stainless steel, bronze and even plastic impeller housing units offer considerably more rust resistance than models with cast iron.

Pump head and flow rate

In all active solar water heaters, the panel or collector is mounted well above the storage tank. Solar hot water pumps are required to overcome this elevation difference . In order to overcome gravity, the water pump must generate enough pressure to circulate the fluid upward as well as through the system. 

And it must do so efficiently and effectively since the flow rate through the solar water panel and the flow rate through the heat exchanger are both important to the water heaters' overall performance.

The pressure, vertical lift or vertical discharge a pump provides is referred to as pump head. The higher the head the more powerful the solar hot water pump.

Feet of Head 

The pressure a pump provides is measured in distance, or feet. Manufacturers often times classify they're hot water circulators using terms such as high head, medium head or low head. Such classifications serve as feet of head ranges.

Cut Off Head

The highest point, in terms of feet, at which a solar hot water pump will provide vertical lift is commonly referred to as the pumps cut off head.

GPM at Head

GPM, or gallons per minute, at head is a classification that determines the fluid volume or flow rate to expect from a solar powered pump at a certain pump head or vertical lift.

High Head Pumps

Medium Head Pumps

  • Ideal for closed loop solar hot water heaters, especially those with moderately sized pipe runs in the loop.

  • Can be used in drainback designs with small sized pipe runs in the loop.

Low Head Pumps

  • Generally limited to direct pump systems. In these designs the pump is only required to circulate fluid through the collectors or panels.

More on pump head

It's important to note, when determining how powerful a pump a solar hot water heater will require, one must always take into account the vertical length of the plumbing pipes within the loop.

Solar hot water heaters with large vertical pipe runs can be retro fitted with two or more medium head pumps, but the solar water pumps must be properly spaced out within the loop in order to achieve a suitable fluid flow rate and overall head.


Drainback solar hot water heaters are designed not to have fluid in the loop when the system is idle. So these systems almost always require a high head solar hot water pump, because there must be enough vertical lift to collect the fluid from the drainback tank before recirculating the fluid through the loop.

It's not advised to install two (or more) medium or low head pumps in drainback systems, particularly if freezing is even a moderate concern. If one solar hot water pump were to fail, the remaining functioning pump will likely be unable to provide a suitable vertical discharge and throughout the loop.

And in the cold season, the undrained fluid remaining in the loop can eventually freeze. This would seriously compromise the entire function of the hot water heater, this could even cause the pipes within the loop to eventually burst.

Power source

Another important consideration to make when selecting a solar hot water pump is determining a suitable power source. There are two options for powering your solar water pump; AC and DC.

AC Solar Water Pumps

AC pumps use the alternating current that's provided by a home's or businesses existing electrical wiring. These hot water pumps utilize just a small amount of this electricity to circulate fluid. The overwhelming majority of AC models use 120 volts. A differential thermostat controller will be required to operate the pump.

DC Solar Water Pumps

DC water pumps use direct current to power the motor. PV modules are used to harness solar electricity, and this energy activates the hot water pumps' motor. There are two types of DC solar water pumps; brush and brushless.

Brush models use carbon brushes to assist the movement of the impeller. These brushes are prone to wear and tear, potentially causing frequent replacement. 

Brushless models rely only on the motor to spin the impeller. Brushless DC solar hot water pumps generally last longer and are known to activate quicker than DC pumps with brushes.

AC Solar Hot Water Pumps vs. DC Solar Hot Water Pumps

Important Characteristics   AC Pumps     DC Pumps  
Greater Potential For Long Term Energy Savings    
solar hot water pump comparison
The Initial Cost Is Generally Less Expensive solar hot water pump comparison
A Wider Range Of Models To Choose From solar hot water pump comparison
High Head Models Are More Readily Available solar hot water pump comparison

Generally Produce Higher Fluid Flow Rates solar hot water pump comparison
Are Generally Quieter When Activated solar hot water pump comparison

More on solar hot water heaters


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