Solar Heating Information

 

How do we use solar energy for solar heating systems?

Solar energy is the single most abundant form of renewable energy in the world. Energy from sunlight can reach the earth's surface with a maximum intensity of more than 1000W/m². Solar heating is the process of taking the solar energy and converting it into usable energy for heating water. Solar energy can also be used to generate electricity. If you are wishing to obtain information on generating electricity you should contact the Sustainable Electricity Association of NZ (SEANZ).

What Solar Water Heating Systems are available?

There are a wide range of models of solar water heating systems available in New Zealand but essentially they have the same basic components of collector, hot water storage tank, means of moving water around the system, and a supplementary heating controller. The solar system is designed so that the various components are integrated, so if you are looking for a solar system you should look for a packaged system.

A packaged system is one which has been properly designed for optimal energy performance. Energy performance can be affected by the collector area, way and time in which hot water is used, when the supplementary heating is added and how the components are integrated. Simply purchasing a collector and adding it to your existing hot water storage tank could result in very poor energy performance. A packaged system can have its likely energy performance modelled so that you know what you are buying.

In New Zealand, most systems installed are pumped (active) systems. These systems use a small circulating pump to transfer the heated fluid from the collector to the storage tank. A controller determines when the water in the collector is hotter than than in the tank, and operates until the collector is refilled with cooler water again. This process continues until the water in the tank reaches it maximum operating temperature.

The fluid in the collectors can be either water in a direct system (the water in the collectors is the same as what comes out the taps), or a diluted glycol working fluid in an indirect system (a working fluid is pumped between collector and a heat-exchanger in the tank).

What types of collectors are available?

  • Evacuated Tube collector: These are long thin glass tubes which have a vacuum layer between the solar absorber and the outside air. The low heat-loss from these tubes make them effective at higher operating temperatures.
  • Flat panel collector: These are large flat collectors usually with a selective surface absorber for water heating in New Zealand. Non-selective surface absorbers are suitable for pool heating, and other lower temperature applications (eg pre-heat systems).
  • Unglazed Collector: These are large plastic collectors used for heating otherwise unheated pools in sheltered locations. They are highly efficient collectors, but only at low temperatures.

    • A Solar water heating system can be supplied as a packaged system or custom built. Where a solar water heating system is supplied as a packaged system it will be supplied with all components (tank, collector, pump, controllers) which have been designed for complementary and optimal energy performance. Systems supplied and installed as complementary packaged systems can be tested for energy performance as packaged systems with nominated sized and type of containers, and any claimed performance relate to the system as a whole.

     A customised system may be constructed for a special application or be where solar components from a packaged system are connected to an existing hot water cylinder. Such systems should only be put together by Approved Installers from components of packaged systems and connected to other existing components such as a hot water storage cylinder. Where systems are custom built using components, suppliers must be able to provide evidence that the individual components meet the appropriate standard tests, and that the customised system as a whole meets any claimed performance levels by demonstrated similarity of performance to a representative product that meets the requirements of the standard.