The study focused on those three appliances because they used a lot of energy and their energy demand could in principle be shifted out of peak demand periods, 6am to 10am and 5pm to 9pm.
At these times generation, transmission and distribution infrastructures run close to or even at full capacity, especially in winter.
Department of Physics academic Dr Michael Jack co-authored the study with Otago Centre for Sustainability director Associate Professor Janet Stephenson, and University of Southampton academic Dr Ben Anderson, a visiting Marie Curie Research Fellow at Otago.
Dr Jack said the challenge of implementing a 100% renewable electricity system in the face of a projected 150-200% increase in demand was a significant one for New Zealand, particularly for dry years when hydro power would not be sufficient to meet demand, creating a risk that New Zealand would have to invest in a new fossil fuel-based generation.
“Power generators, Transpower and electricity network companies build infrastructure to cope with peak demand.
"If we can reduce peak consumption by shifting use out of peaks we will be taking a big step towards achieving our future targets without burdening households and the country with extra costs, and without increasing carbon emissions,” Dr Jack said.
Hot-water cylinders, heat pumps, and refrigerators constitute 50% of the total residential electricity consumption in New Zealand.
Dr Anderson said if the shift was well-managed, the energy services provided by the appliances would remain the same.
“Water will stay hot in the cylinder for people’s morning showers, living spaces could be pre-warmed before 6am via smart thermostats, and fridges could remain cold despite being switched off for a short time during peak. The combined result of these interventions across millions of New Zealand households could be substantial,” Dr Anderson said.
Associate Prof Stephenson said the projections contained in the study were the first stage in determining what would be achievable in reality.
“Future work will need to consider the market systems, technologies and consumer behavioural change necessary to achieve residential demand response in practice, and how consumers would respond to the opportunity to shift their demand,” says Associate Prof Stephenson.
The report, Estimating the Technical Potential of Residential Demand Response in New Zealand: A Summary of Results, has been prepared by researchers at the University of Otago as part of the GREEN Grid Project funded by the Ministry of Business, Innovation and Employment.