Solar Water Heating – Frequently Asked Questions

1. Can a solar water heating system be used in place of a traditional gas or electric heating system?

In order to ensure proper efficiency of your water heating system, a solar energy system should be used in conjunction with a traditional gas or electric heating system, rather than as an alternative to a traditional system.

2. Do solar systems produce hot water in winter or on a cloudy/overcast day?

Yes. Our Solar Water Heaters can be used all year round in all regions of New Zealand and can provide all of your hot waters needs on clear or intermittently overcast days. If it is particularly overcast or raining, electric or gas automatic backup may be required.

Although the efficiency of the solar collector is reduced on overcast days it will still be able to heat water for normal use. If it is a heavily clouded day or raining, then gas or electric backup may be required to maintain water at the required temperature. This system will be automated so you don’t have to worry about running out of hot water on a rainy day.

3. Are Vacuum Tube Collectors more efficient than flat panel collectors?
On average, yes. Vacuum tube collectors are superior to flat panel collectors in a number of ways.

• Due to the cylindrical shape of the vacuum tube, the sun is perpendicular to the surface of the glass for most of the day. Flat panel collectors have the disadvantage that the sun is only perpendicular to the collector at noon and thus a proportion of the sunlight striking the surface of the collector is likely to be reflected.
• As the name suggests, air is evacuated from the vacuum tube to form a vacuum. This greatly reduces conductive and convective heat loss from the interior of the tube. As a result wind and cold temperatures have minimal effect on the efficiency of the evacuated tube collector.
• NZ Solar Vacuum tube collectors can often be used in subzero temperatures without the system sustaining damage. Flat systems often require expensive and complicated “antifreeze” systems to be installed.
• Vacuum Tubes are strong, long lasting, and should one be broken, inexpensive and easy to replace.
• Due to the high efficiency absorption of solar radiation even during overcast conditions, combined with excellent insulation properties of the tube, vacuum tube collectors will heat water all year round (automatic backup may required for particularly overcast or rainy weather).
• Due to the various advantages of vacuum tube collector over flat panel collectors, a smaller collector can be used to provide the same heating performance. For example, a standard household of 4-5 people would usually require a 250-300L water storage tank. Depending on your location, only 2.1 – 2.8 square metres of evacuated tube surface area would be required to efficiently heat this volume of water.
• Flat panel solar collector can produce similar heat output to vacuum tube collector, but generally only during warm, still, sunny conditions. When averaged over an entire year, vacuum tube collector heat output per net m2 of collector area is superior to flat panel.

4. Can I use a solar collector with my existing hot water system?
Most often times solar collectors can be used with an existing system by utilizing a simplistic solar conversion valve that connects to your existing water tank.

5. What happens if one of the solar tubes is broken?
The tubes are very strong and not easily broken, but can be replaced very easily should one break due to extreme conditions. They are inexpensive and available though your local distributor. The system can operate with several broken tubes, but the efficiency will be reduced, so it is recommended that broken tubes be replaced immediately.

6. What is the payback/ROI of the system?

Depending on factors including geographic location of the system, insolation levels (amount of solar radiation) in that area and annual usage of the system, an average household of 4 can expect to recover the cost of a solar system within 4 to 6 years.