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Green Energy



What is a solar hot water system?

A typical solar hot water system is made up of solar collectors, a storage tank, a gas or electric booster and a solar controller and pump for split systems.

There are two types of systems available

  1. Close Coupled systems
  2. Split systems

Close Coupled systems have the storage tank above the solar collectors all located together on the roof. Close Coupled systems rely on thermosyphon to operate: cold water from the bottom of the tank falls to the inlet at the bottom of the solar collectors. The water is heated by the sun, rising up through the solar collector and back into the middle and top of the tank.

Split systems have the storage cylinder located on the ground and the solar collectors located on the roof. Split systems use a solar controller and pump to transfer cold water from the tank to the solar collectors to be heated and returned to the middle or top of the tank. The solar controller compares the temperature of the water in the solar collector to that in the tank. When the collector is hotter than the tank the pump is switched on, transferring the solar heated water to the tank.

Why use a solar (thermal) hot water system?

Installing a solar hot water system has great benefits especially when replacing an electric storage tank. It can potentially reduce electricity consumption, running costs and environmental impact by 2/3rds.

40% of a typical households electricity is used for heating water. Therefore a solar water heater can potentially reduce the overall electricity use by 25%.

Australian electricity is predominantly generated using non renewable and dirty coal fired power stations. As well as electricity they produce carbon dioxide emissions, ash, particles and waste heat, while consuming vast quantities of water and non renewable coal.

Rinnai solar hot water systems reduce the need for electricity and are part of many major energy reduction programs. Solar hot water systems also offset electricity just when it is needed most: Summer – as that is when air conditioners are running, loading up the electricity network.

Will I get solar gain in winter?

Solar gain is available during the day throughout the year. Even cloudy days can deliver some solar gain. A clear winter day may sometimes deliver more solar energy than a cloudy summer day.

  • Clear and sunny days produce high solar contirbution
  • Clear and cold days produce reasonable solar constirbution
  • Overcast and warm day produce reasonable solar contribution
  • Overcast and cold days produce low solar contribution

How do I size a solar hot water system?

The storage tank should hold a one days supply of hot water and have enough capacity to store the amount of solar energy collected by the solar collectors. Once the tank size is chosen to match household hot water use, the number of solar collectors is matched to the tank. 


What is a solar collector?

The solar collector is the most important component within the system as it absorbs the energy from the Sun and heats the water. Collectors are generally made up of a combination of:-

  • A glass surface (flat on a flat plate collector or round for evacuated tube collectors)
  • Tubes containing a fluid that is to be heated by solar energy
  • Heat absorbing surface / fins attached to the tubes
  • A treated surface on the absorber to capture and retain solar radiation
  • A casing / vacuum to retain heat
  • Pipework to enable the transfer of solar energy to the storage tank

The solar collectors are roof mounted and ideally face North when installed in Australia. Facing East or preferably West is OK, but a reduced amount of solar energy will be collected. 

Avoid having the collectors shaded by adjacent buildings, structures and trees.

What type of solar collectors are available?

There are two types of Solar Collectors:

  1. Flat plate
  2. Evacuated Tube

Flat Plate collectors are made up of an insulated tray style case with a sheet of low iron solar glass on the top surface. Beneath the glass is a solar collector surface, either one piece or multiple fins. This has multiple water / fluid channels attached to it.

Sometimes known as a panel a flat plate solar collector is perfect for non frost areas and close coupled systems.

Evacuated tubes comprise sets of borosilicate glass “test” tubes with an inner glass tube providing a vacuum for heat retention. The energy that the tubes collect is transferred to the consumable hot water inside a well insulated header assembly. Evacuated tube collectors are available in cofigurations using either 20,25 or 30 tubes.

Frost prone areas are ideal locations to install evacuated tube solar collectors as they can withstand temperatures as low as -12°C. They must be installed on a split system.


What is the difference between Solar Thermal Collectors and PV Panels?

They are separate solar energy collection technologies.

  • Solar (thermal) hot water systems convert radiant energy into hot water.
  • Photovoltaic (PV) solar converts radiant energy into electricity.


What are Small Scale Technology Certificates (STC’s)?

The Australian Government lists solar water heaters that are eligible for STCs and are therefore eligible to receive a rebate based on the number of STCs awarded. 

An STC is a calculation of how much energy is expected to be saved over ten years when using a solar water heater compared to the electricity consumption of an equivalent electric water heater. 1 x STC is 1 x MWh of electricity saved over 10 years = 100 kWh saved in a year.

Performance calculations take into account geographic location, solar radiation, the angle of the sun, the efficiency of the solar collector, tank heat loss, cold water temperatures, the quantity of hot water used and hot water usage patterns.

The more STCs awarded to a system equate to a higher rebate available on the purchase of that system. Visit our solar rebate estimator to find out more.

Why do I need a booster for my solar system and what types are available?

A booster is required to deliver hot water in times of low solar contribution or times of excessive hot water consumption.

There are 2 booster options available:

  • Gas
  • Electric