solar hot water system installed on a house

Why and how to choose solar hot water systems?

Solar thermal systems are exceptionally good at heating water.  They harvest a high proportion of solar energy hitting their surface and store this heat energy in a cylinder for later use.  Because heat energy is transferred directly they operate at very high efficiency, maximising the solar energy harvest for every square meter of collector.  For example, an Apricus ETC30 collector has 2kW peak output for 4.4m² collector, operating at 60% – 70% efficiency at domestic water temperatures. 

Heating water is almost always the single largest user of energy in individual homes.  In new homes, with improved insulation, energy efficient appliances, heating & lighting, water heating uses an average of 46% of the home’s energy (electric lines company figures, 2014-16).  Other buildings (accommodation, apartments, sports centres, hospitals) will also have relatively high energy use for water heating.

In these buildings and individual homes solar thermal should be the first option to consider when specifying hot water systems and renewable energy technology. 

A high quality, well designed & installed solar thermal system will reduce energy for water heating by around 75% in individual homes and by 40-70% in larger buildings.

How to choose between solar hot water systems?

The ultimate performance of a solar thermal system relies of four aspects:

  1. Appropriate, full system design
  2. Quality & longevity of collectors and other system components
  3. Installation quality
  4. Eliminated or minimised on-going maintenance cost


Individual domestic systems have the most straightforward design and need to include careful consideration of booster heater control and ease of use by homeowner. Project specific design and modelling are crucial for larger systems, undertaken by a suitably experienced solar hot water professional.  

System Quality & Longevity:

NZ does not have published, comparable performance data for solar thermal systems.  Therefore, collector performance is best assessed using international certification – SRCC from USA, Solar Keymark from Europe.  These provide comparable performance data for collectors plus rigorous manufacturing quality standards.

The other system components should be solar rated, high quality and from reputable suppliers and manufacturers.

Also check the length and comprehensiveness of system warranties, plus the history and reputation of the organisation and therefore likelihood they will be around to fulfil warranties.

Installation Quality:

A well-designed, simple system with high-quality components, plus good technical support, should be able to be installed by all good quality plumbers.  As the complexity of the system increases so too does the potential for installation errors, especially if a “closed loop” solar circuit is involved.  In NZ these issues can largely be avoided by choosing an appropriate use of technology: open loop for evacuated tubes and drain back for flat plates.

In larger systems the solar supplier should attend the site for commissioning and as-built sign-off.

Eliminated Maintenance:

Regular or costly maintenance should be avoided by consideration of the three aspects above.  To cover all eventualities, ask the system supplier to provide a guaranteed and costed maintenance schedule.

Establishing a relationship with a supplier who can fulfil all these criteria should help ensure that all your clients can start to benefit from solar heated water.  By specifying well-designed, long-lasting and high-performance solar thermal systems we can significantly reduce the energy use, environmental impact and running costs of heating water in our buildings.

Find out more about Apricus Solar Hot Water

Apricus Eco endeavours to ensure that the information provided in this blog article is reliable and accurate at the time of publishing, please note that the information detailed can change with the passage of time.