The Alternative Energy Company supplied and installed a solar thermodynamic water heating system for the new Cardrona Waste Water treatment plant. The new plant, designed and constructed by Apex Water, serves the Cardrona village, the Cardrona Alpine resort and a new residential and commercial development in the valley. The plant was commissioned in September 2020.

The alpine environment required some innovation for the plant to operate efficiently. In particular, the temperature of the wastewater had to be maintained at an optimum temperature for the bacteria to perform effectively in the treatment process. Direct electric heating was ruled out as inefficient, gas heating was unacceptable due to increased greenhouse gas emissions and direct solar heating would be ineffective during winter. Solar thermodynamic heating was the solution.

The system consists of 32 solar thermodynamic panels and a Solar Block unit. The solar thermodynamic system can take heat from the environment even in snowy winter conditions and at night.

In his paper to the Water NZ conference Dr Matt Savage from Apex Water Ltd says, “The solar thermodynamic heating system was able to maintain the reactor temperature above the critical nitrification temperature under all operating conditions. This included through July 2022 when the panels were covered in snow for a week.” In his conclusion, he says “Solar thermodynamic heating represents a viable low carbon emission alternative to fossil fuel heating of wastewater in extreme cold climate environments.”