SR188 The performance of solar water heaters in New Zealand (2008)

This report examines the performance of solar water heaters and follows on from BRANZ Study Report SR184, which looked at the installation practices for these heaters.

The performance of 39 solar water heating (SWH) and heat pump water heating (HPWH) systems were examined by measuring key performance parameters of the systems over the course of one year (or over the summer in the case of the HPWH systems).

Systems were selected in Auckland, Wellington, Christchurch and Dunedin, with four technologies examined: pumped evacuated tubes, thermosiphon flat plate, pumped flat plate and air-to-water heat pumps. The measurements, however, showed that the individual systems and their installation were more important than any effect due to the technology used or the region and climate for how much renewable energy the system can supply.

A range of performances was seen. On average, 38% of the annual household hot water heating needs (or 1,260 kWh/year) was supplied from the sun for the monitored SWH systems. A set of higher-performing systems (about 27% of systems) was identified, which provided an average of 2,060 kWh/year of energy from solar with an average fraction of the energy coming from solar of 43%. Another lower-performing set of about 21% of systems was identified with these systems contributing on average 550 kWh from solar or 26% of the total water heating needs for these households.