An Introduction to Solar Hot Water Systems

Alongside photovoltaic panels, solar hot water systems are another great way to harness the sun’s energy to reduce a property’s electricity bill.

Convection is used to move heated water toward the insulated cylinder

Convection is used to move heated water toward the insulated cylinder

Government information on hot water figures estimate that the average house with an electrical hot water system can attribute 30% to 40% of their energy bills towards heating water. Gas hot water systems can see a much higher percentage, with only a handful of kitchen and heating appliances contributing alongside hot water to the gas consumption. More broadly, an average of 20% of household greenhouse gas emissions are produced from the energy used to heat and store heated water.

The motivations for renewable energy sources are now more than ever being promoted and supported by environmentally aware sources. With the presence of state and federal governmentally sources financial incentives on the market now and into the future, the motivation needed for such a change has been found. The following is a quick introduction into the solar hot water industry, beginning with an overview of what is available, and what it can do for your property.

Two main types of SHW system

On most residential and small scale commercial property’s there are two project types; a roof-mounted system and a split-system. The simple difference is that a roof-mounted system sees the installation of both the energy collectors and the storage tank on the roof next to one another. A split-system installs the collectors on the roof and the storage tank at ground level, ideally located within close proximity to the primary usage area of hot water, such as a main bathroom. The efficiency differences between the two are negligible, with decisions usually coming down to roof space and weight support, and aesthetic preferences. Among these two project types, there are two main systems that are installed in Australia and throughout the world. They can both be either roof-mounted or split.

Flat Plate SHW System

These systems consist of glass panels sitting above copper piping on a roof, absorbing the heat from the sun’s rays as they strike them much like a solar energy system. The copper piping, using the simple notion of rising heat, circulates the water around the system, storing the heated water in a tank either on the roof horizontally or beside the house vertically, which sits above the panels.

This thermo-siphoning sees the constant displacement of cooler water to the bottom of the panels to be heated, whilst simultaneously pumping the heated water throughout the house.

They usually feature a gas or electric booster, which kicks in as required when there is insufficient hot water being generated or stored by the Flat Plate system. Such times may refer to low-sunlight or high hot water consumption periods. An electric booster is fitted to the storage tank and heats the water if the temperature drops accordingly, whilst a gas booster is connected to the piping and heats the water if required as it passes through a fitted solar transfer valve.

Evacuate Tube SHW System

Evacuated tube systems, otherwise known as streamline split-systems, involve the use of glass tubes being mounted on the roof, usually arranged in a couple of panels. The panels then absorb the heat from the air, not the direct sunlight, and transfer this heat to the copper piping that runs underneath. These pipes transfer the heated water to a storage tank usually at ground level, which insulates and stores the hot water. The cooler water in the system is moved by a circulator up to the piping nearest the panels on the roof, and is heated in turn.

Again, a gas or electric booster is usually required in order to ensure that hot water is available during times of excessively cold, cloudy weather.

Comparison of Flat Plate and Evacuated Tube systems

Depending upon where the property is located, what environmental conditions it is installed in, the budget of the project and the overall hot water usage, either a Flat Plate or Evacuated Tube system should be considered advantageous.

Evacuated Tube systems:

  • Have a greater surface area to volume ratio on the panels, thus absorbing more of the heat around them
  • Can operate more effectively during overcast weather conditions
  • Are not prone to freezing or corrosion
  • Require a smaller roof space.

Flat Plate systems:

  • Are usually cheaper
  • Can transfer the heat they absorb more effectively to the water required, due to a lower, more consistent volume being pumped through the system
  • Are much more resistant to hail damage

Ultimately, the Australia Federal Government requires that all renewable energy sources are evaluated based on their energy efficiency. This is in order to establish how many Renewable Energy Certificates (RECs) they should be allocated. It can be assured that whichever system has the higher amount of RECs assigned to it is the most efficient, and therefore the most environmentally sustainable. This assessment should weigh heavy on the minds of any prospective installer of a solar hot water system.

Retrofit additions

There is also the possibility of a retrofit system for people that have an existing gas or electric hot water system, but wish to install the evacuated tube panels in addition, to take some of the load out of their existing booster. This would see Evacuated Tube panels be installed on the roof much like with an original system. The difference would be that the existing system would take over much like the gas or electric booster would, in times of excessive use. It must be noted that the rebates for such an upgrade to an existing hot water system are different, a matter that will be covered in another blog entitled; œSolar Hot Water Rebates.

Tank sizes

Storage tanks differ in sizes based on how many Litres (L) they can hold. Different solar hot water installers will offer different sizes based on the most commonly desired sizes and living arrangements. It is estimated that a 300L system will comfortably suffice for a household in which 4 to 8 people live. Most installer start their sizes at the 180L mark though, so there is a lot of room for negotiation based upon your hot water requirements.

Solar Hot Water System pricing

In conclusion, there are a number of factors that can affect the financial outlay of a solar hot water system being installed on your average home or small scale industrial or commercial property. These include;
¢ If you are entirely replacing your hot water system (new project) or after the installation of solar-based additions (retrofit).
¢ Whether you are after a Flat Plate (less efficiency and cost) or Evacuated Tube (more expensive and effective) system.
¢ Tank size (proportionally increases).
¢ Eligibility for state and federal solar hot water rebates.
(Another Solar Choice blog on this website titled œSolar Hot Water Rebates explains the availability and effectiveness of such rebates.)

Ultimately, these factors must stack up against the prime financially motivating factor of getting a solar hot water system installed; the savings on your energy or gas bill.
The most effective way to evaluate one’s potential savings with regards to the installation of solar hot water is to get an accurate fix on the average load that heating water places on your energy or gas bill. Once this figure has been established, it becomes the simple manner of foreseeing that amount of money being taken off the quarterly energy and gas bills and being placed into your pocket, or at least the whole that was created there when you had the system installed.

Once these figures have been established, ask yourself how long it would take for that amount of savings to reach the cost of the installation. If the number of quarters seems like it’s within your grasp, then perhaps the financial motivations have been found.

It must be noted that not 100% of the energy or gas used previously to heat a property’s water will be produced by the solar hot water system. As mentioned previously, gas or electric boosting may be needed in times of bad weather or high consumption. Exactly how much of an impact this has depends on the tank size and usage involved.

Tips for hot water savings

¢ The majority of households in Australia will be classed as ˜heavy’ users. Light users will have quick (less than 5 minute) showers and cold water wash clothes.
¢ Check your bill for details regarding peak or off-peak electricity usage.
¢ If your gas heater was installed prior to 2002, choose the ˜older gas heater’ option.
¢ If you use a gas heater rated 2 Star or less, choose the older option.
¢ If you use a gas heater rated 3 Stars or more, choose the new gas heater option.

Annual Savings on a Solar Hot Water System

Hot water use

Peak electricity

Off-peak electricity

Old gas heater

New gas heater

Light (n)

Heavy (n)












































n=number of people

Jarrah Harburn
Solar Broker
Solar Choice Pty Ltd

© 2009 Solar Choice Pty Ltd


  1. hello
    I am writing to get some advice on a Chromogen solar H/W(200l) unit with electric boost. We recently did some calculation on the power usage of the system over the summer quarter and found that it consumed a whopping 17 KWhrs per day on a timed circuit dedicated for off peak. Concerned that it was considerably higher than was expected we investigated further. Upon inspection we found that wiring to the element via the thermostat on top of the tank was scorched. I have concluded that the element might have a partial short circuit causing excessive electricity use. Is this a fair assumption or could there be another reason underlying the high electricity consumption.

    Any advice would be appreciated
    Thank you
    Marcus Power

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