Before installing a solar water heater, it is worth investing some time into checking the technology is best suited for the site and location.
Exposure to rays
Consider the number of hours of direct sunshine available on the roof each year. The more hours a site has, the more water heating can be gained but clouds and haze will limit available sunshine. For effective solar water heating, at least four hours of sun on the solar panel during the middle of a winter’s day is required.
Shade must be minimised for the best performance of any solar system. Look at the house and the proximity of neighbours, hills and trees. In winter, obstacles on the north side cast shadows two to three times their height, so tall objects should be at least six metres away.
Consider if there are likely to be any changes over time which will shade the site – new buildings, for example. Sun path and angle also change with season, so sometimes hills and obstacles will create shade at different times of the year.
About five to eight square metres of the roof needs to face north. Alternatively a frame can be used to support the panels facing this direction. The roof needs to take the weight of a solar system, which is particularly important if a roof-mounted hot water cylinder is chosen.
If household usage peaks in the evening, after a day of solar heating, a solar water-heater may be a good option.
Once a homeowner is satisfied there is adequate sun and a suitable position for a solar water heater, the next step is selecting the right one and installing it correctly.
Model and installation
Solar water-heaters allow electricity to heat water if there is not enough sun. But if the system immediately reheats water with supplementary electric heating after early morning water use, solar energy will not be used effectively during the day.
A timer set to exclude electric supplementary heating in the mornings is a simple and practical way to avoid this.
The panel area needs to be large enough for the demand and with a large panel area, a large hot-water cylinder is also necessary to store hot water for later use.
Optimal installation for year-round hot water requires installing solar panels at the same angle as the latitude of the location. This latitude varies throughout New Zealand with Auckland around 37 degrees south, Wellington 41 degrees south, and Dunedin 45 degrees south.
Panels are often installed on the same angle as the roof – typically with a pitch of around 25 degrees, which is an insufficient angle to get good winter performance in most of the country.
Insulation must be appropriate for New Zealand conditions and pipe lengths should be short and well-insulated, especially if the cylinder is outside.
For more information, visit www.beaconpathway.co.nz.
