Beacon

Solar water heaters have received flack in the past for falling short on their promises. This poor reputation, however, is somewhat underserved.  Recent research has shown that the quality of performance is inextricably linked to installation and product selection; get these two right and solar water heaters can be an effective solution.

Beacon Pathway has used solar water heaters in five research homes.  Two were new homes, the Waitakere NOW Home® and the Rotorua NOW Home®.  Three were renovations to homes in the Papakowhai Renovation project.  Monitoring has told us a lot about how well the solar water heating systems worked and how to optimise their performance.

 

Timers and Controls

Timers and control displays can optimise performance.  Solar water heaters allow for electricity to kick in and heat the water if there is not enough sun.  But if the system immediately re-heats the water with supplementary electric heating after early morning water use, you miss out on using solar energy to re-heat the water during the sunny parts of the day.

Selecting a solar water heater with a timer that is set to exclude electric supplementary heating in the mornings is a simple and practical way to avoid this.

Also, look for a system that provides information about how the system is operating to help the household understand when it needs hot water and when the sun provides it.

 

This display in the Waitakere NOW Home showed the homeowners exactly what temperature their solar system was providing

 

 

 

 

 

 

Sizing of System Components

Ensure that the collector area is sufficiently large for the demand required.  Our Papakowhai systems connected two twelve-tube panels to form a large collection area - and their performance far surpassed the other, smaller, systems.

With a larger collector area, you will also need a larger hot water cylinder (300L cylinders matched the panels in Papakowhai) to ensure you can store the solar energy collected during the day for later use when hot water is required.

 

Collector Orientation

The sun shines from the north, so any surface facing north (preferably in a range of 20^oW to 30^oE of true north) will capture sun. True north can be found from local maps and street directories; or use a rough visual while on the site - the line between you and the sun at midday is an estimate of true north.

 

Collector Angle

We call on more hot water in winter than in summer, and ensuring that the winter-time performance of a solar water heating system is optimal will produce plenty of hot water even in winter sun. Tilt angle is the angle of the solar panels in relation to the ground. Latitude varies down New Zealand: Auckland is around 36°, Wellington 41° and Dunedin 45°.

Ensure the solar panel (collector) is installed at the same angle as the latitude of the location to get the best year-round performance. 

 

Reducing Heat Losses

Ensure that heat losses from the systems are kept to a minimum.  Make sure that insulation levels on cylinders are appropriate for New Zealand conditions and that pipe run lengths are kept short and well insulated.

 

Related Documents

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  30-Jun-2009 (Report HR2420/8)

  Solar Water Heating in the Waitakere and Rotorua NOW Homes and in three Papakowhai Renovation homes (PDF 1.3MB)

  Andrew Pollard

  This report describes and examines the performance of the solar water heating systems used in the Waitakere NOW Home®, the Rotorua NOW Home® and three of the Papakowhai Renovation houses. A variety of systems were used in these houses and performance varied from 75% of the water heating being provided by solar in one of the Papakowhai  Renovation houses to 36% of the water heating needs being met by solar in the Rotorua NOW Home®.  Reasons for the performance levels are suggested. 

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