A four year study on energy usage in New Zealand households warns current trends will not be sustainable when the country makes the complete switch to renewable energy.
The NZ Green Grid project investigated the energy usage of 45 North Island properties, and isolated the energy use down to what appliances were using the electricity.
The study found increased heatpump use over winter and the increase use of electric vehicles could use more energy than what is presently possible from renewable sources.
It also found the average house had between two and three appliances for refrigeration.
Energy Research Centre co-director Michael Jack said the infrastructure and market structures needed to change.
"Wind is variable. It's only generating when the wind blows.
"Solar is generating during the middle of the day, when there's less demand for it.
"What you need to do is either shift your demand to those time when the renewables are being produced or somehow store those renewables for use at later times," he said.
Dr Jack said one possible option was using heatpumps that were set on a thermostat, where temperatures could be lowered during certain hours of the day.
He said if changes were not made, the switch to completely renewable energy would be a costly.