Solar water heating system components

For optimum performance out of a solar water heating system, the different components must work together to store the right amount of sun-heated water for your needs, while minimising the need for back up heating.

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Components of a solar water heating system

The main components of a typical solar water heating system include:

  • The solar collector (panels)
  • The storage tank (cylinder)
  • The circulation system
  • Controller or timer.

In a packaged system all the components are chosen for you to ensure your solar water system is as efficient as possible.

It's important to look at how a whole packaged system performs rather than just the individual components. EECA publishes the performance modelling data for all solar water heating systems qualifying for an ENERGYWISETM $1,000 grant.

To compare the performance of these solar water heating systems, check the information on finding the right solar water heating system for you page.

How the components work together

The collector absorbs the sun's energy and this heat is transferred to the water in the storage tank (or cylinder) by the circulation system. How efficiently this is carried out depends on the performance of each component and how well they are matched together as a system.

The size of the solar collectors needs to be matched to the hot water tank, and together the collectors and tank need to be matched to your hot water usage. If your collectors or tank is too small or too big you will be paying extra to boost the temperature of the water.

Timers, thermostats and controllers are other important components that contribute to the efficiency of your system. These, for example, will ensure that the backup heating is not heating water that would otherwise be heated by the solar heating system. While doing this, they'll also ensure there's enough hot water available when it's needed.

A properly insulated system (pipes and tank) is also very important. This helps to reduce the amount of heat lost while the hot water is being stored and circulated around your house.

Solar collectors

There are two main types of solar collectors for solar water heating systems:

  • flat plate collectors; and
  • evacuated tube collectors.

Generally, flat plate collectors and evacuated tube systems can be equally effective at using the sun's energy, but performance also comes down to how well all the components work together. To compare the performance of solar water heating systems, check out EECA's list of solar systems that are eligible for a grant.

A flat plate collector looks similar to a skylight. It absorbs sunlight and transfers the heat into the water (or heat transfer fluid) flowing through the collector panel. A typical house would have around 1m2 of collectors per person in the house.

An evacuated tube collector is made of a series of glass tubes between 1.5m and 2m long that slope lengthwise up and down the roof. A typical house would have around 5 to 10 tubes per person in the house.

Usually solar collectors are positioned on your roof. However, an in-roof installation option is also available. In-roof solar collectors are put into the roof in a similar way to a skylight. It is also possible to mount solar collectors at ground level, which can reduce the installation costs.

Storage tanks

In solar water heating systems, the storage tank can be part of the system on the roof or set up in another area of the house.

You can use a conventional hot water tank or a specialist solar water heating tank. A specialist solar water heating tank has extra connections for the solar collectors and multiple element locations so the system can be configured to maximise the use of solar energy without compromising on hot water delivery. Your system is likely to perform better with one of these.

Historically, domestic hot water tanks were around 180 litres in capacity. This is generally too small for a solar water heater to achieve optimal performance for a household of three or more people. A properly sized solar water heating system may have up to 100 litres of storage per person, compared to around 50 litres per person on a standard electric hot water system.

Open or closed loop

Open or closed loop refers to how the collectors and tank are connected together.

In an Open loop systems the water from your tank circulates through the collectors on your roof, where it gets heated up and then returns to your hot water tank.

With closed loop systems, a heat transfer fluid (usually a mixture of water and anti-freeze) circulates through the collectors. This fluid passes through a heat exchanger in your hot water tank, heating up the water. The heat transfer fluid and the water in your tank don't mix.

A closed loop system could be a good option if you live in an area with frequent frosts in winter or if you have hard water. Check your kettle - if it has a build up of minerals on the element, you have hard water. In an open loop system these mineral deposits can build up in the collector over time and reduce the performance of the system.

Talk to your supplier or installer about which system is best for you.

Circulation system

Water or fluid can be circulated around a solar water heating system using a pump, or it can circulate without a pump, in what's called a 'thermosiphon' or 'passive' system.

Systems that use pumps to circulate the water or fluid are often called 'active systems' and require a small amount of electricity to work.

With a pump system, the hot water tank can be positioned below the collector panels or in a different part of your house. This can be helpful if you want to use an existing hot water tank, or if you don't want to see the tank on the roof.

Controllers must be used to turn the pump on when there is enough solar energy available and off when there is not.

In passive systems, the storage tank is located above the collectors, usually on the roof, but sometimes within the roof space. Cold water or heat transfer fluid sinks from the tank into the bottom of the collectors. Once it's heated by the sun it naturally rises to the top of the collectors and back up into the tank.

Thermosiphon circulation doesn't require a pump and isn't dependent on electricity to work.

Controllers

A controller manages the use of supplementary or 'booster' heating in solar water heating systems. If there's a pump, it controls this also. The control of the supplementary heating can greatly affect overall system performance, so it's important to have the controller set correctly.

There are two main types of booster heating control, minimum temperature (thermostat) control and timer and minimum temperature (thermostat) control

Minimum temperature (thermostat) controllers

These:

  • are used in all controllers
  • turn on supplementary heating when the stored water temperature falls below a preset minimum.
  • increase system efficiency
  • ensure hot water is always available
  • work best in solar specific storage tanks with the heating element at half height.

Timer and minimum temperature (thermostat) control

The addition of a timer to the controller:

  • only allows supplementary heating to come one at certain times
  • maximizes the use of solar energy
  • may mean insufficient hot water is available at certain times
  • works best in non solar specific storage tanks with the heating element at the bottom.

All controllers should be mounted where they can be seen so that if a fault in the system is detected the homeowner can be alerted.

Some controllers can also display:

  • the energy saved by the system
  • whether there is enough solar energy to turn on the pump
  • whether the booster heating is on/off, and;
  • temperatures of the tank and collectors.

Supplementary heating

The supplementary heating for a solar hot water system can come from any heat source, but the most common are electricity, gas and less commonly a log burner or pellet fire with a wet back.

Electricity - If you are considering using electricity for supplementary heating, using night rate electricity could save you money. Find out if any of the electricity retailers in your area offer night rate electricity and ask your solar water heater supplier if their systems can use it.

Gas - Supplementary gas heating can be a booster on your storage tank, but a more efficient option can be an instant gas heater that boosts the temperature of the water from the solar water system as you need it. Normal instant gas water heaters won't work though, it needs to be a model that is designed to boost solar hot water.

Frost protection

In frost-prone areas you'll need to ensure your system has frost protection. This is important as the water or could freeze in the collectors and significantly damage them otherwise.

In open loop pumped systems, temperature sensors can turn the pump on to run water through the system before the collectors freeze. However, this method of frost protection won't work during a power outage or if the pump develops a fault. Some suppliers don't warranty their collectors for frost damage so ensure you get the right system for your area.

Some open loop thermosiphon systems have frost valves. These let the water drain from the collectors when the temperature is close to freezing.

The water/glycol mixture used in most closed loop systems has anti-freeze properties.

Frost tubes are also available on some systems. These enable the water in the collector panels to freeze without causing damage. The tubes absorb any pressure build-up created by the water expanding as it freezing.


Talk to your supplier or installer about the type of system that is most appropriate for you and your location.

More information

Choose the right solar water heater
Installation and maintenance
Solar calculator
Apply for a solar water heating grant

 

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