Energy

Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Solar water heating

Solar water heating systems are highly energy efficient but, for best performance, must be designed and installed correctly.

Solar water heating is energy-efficient, has low running costs (typical water heating costs may reduce up to 75% in summer and 2545% in winter) and has low greenhouse gas emissions.

However, solar energy is variable, and systems will not be as effective on cloudy days, so a booster system is required to provide water heating in periods of high demand or low solar gain. Solar water heating systems can also feed into other water heating systems such as instant gas.

Key design decisions will include the size, location and type of the collector panels; whether to use an open or closed loop heat transfer system; whether to use a pump or thermo-siphon for heat transfer; and the size, location and other specifications for the cylinder.

An important factor in the efficiency of solar water heating systems is how systems are configured and how well they have been installed. It is generally more expensive to retrofit a solar water heating system in an existing house than to install a system in a new construction.

Some solar water heating products now come with an EECA Energy Star rating. This means that when sized and installed correctly, they will typically save 70% of annual water heating costs. Products with an Energy Star have a 10 year warranty on the collector panel, 6 years on the storage tank and 2 years on the controller.

The Solar Association of New Zealand is the industry body for solar water heating solutions. The association has an accreditation system for retailers and installers.

Code requirements

For general Building Code requirements relating to water heating, see hot water supply in the Water section of this site. For requirements relating to storage cylinders, see storage cylinders.

In addition to those general requirements, Clause G12/AS2 provides an acceptable solution for the installation of solar water heaters provided that:

  • the system does not include a cylinder on the roof
  • the building is not too windy
  • the system has a collector that is no more than 4 m2 and is below weight restrictions
  • the system has a collector that is not attached at a angle below 45 to the ground.

The acceptable solution sets out among other things requirements for structural support, materials, system sizing, location of collector panels, and installation.

More information

 

Updated: 13 September 2017