The water flows through the hydros as it falls the 30 metres from the upper dam into the lower dam, transferring energy to power as it goes. The power generated is used to run the water treatment plant however, it doesn’t stop there. Power generated from the four mini hydros far exceeds council’s demand. So much excess power is generated each year that it could also supply 120 Palmerston North homes for a whole year.
“It’s a great scheme that utilises the energy that would otherwise be wasted,” Dora Luo, PNCC’s water asset engineer said. “In winter when there is plenty of water stored in the dams, we operate all four hydros and sell the surplus power to the national grid. During the drier summer months we try to retain water in the dams and only operate the hydros when the water treatment plant’s power demand is high. We release the water through the hydros for what we need for the city while generating power in the meantime. So nothing is wasted. ”
At least 600,000 kWh of power is produced every year via these generators. Last year the mini hydros generated twice as much electricity than used at the water treatment site and the capital cost was recovered four years after the commissioning.
The council’s renewable energy projects, including landfill gas and biogas generators at the wastewater treatment plant, are able to generate, on average, 30% of the quantity of electricity imported from the grid across all their sites – including street lighting, saving the Council over $400,000 in imported electricity costs.