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Rather than pushing for large-scale uptake of rooftop solar power, New Zealand needs to focus on improving the energy efficiency of its buildings, University of Otago researchers argue.

Michael Jack image
Associate Professor Michael Jack.

Associate Professor Michael Jack, Director of the Energy Programme in the Department of Physics, says buildings are responsible for 37 per cent of global energy-related greenhouse gas emissions and are a key focus of decarbonisation strategies internationally.

“Many countries are considering going beyond highly-insulated, energy efficient buildings, to net-zero energy buildings that generate their own energy, often via solar PV, and meet all their energy needs on an annual basis,” he says.

In a study, published in journal Energy and Buildings, he and co-author Hannah Konings explored what impact such a move would have on New Zealand’s highly renewable electricity grid.

They quantified the seasonal variability caused by large-scale uptake of solar-powered net zero energy buildings in New Zealand in order to explore its impact on the electricity grid in comparison to energy efficient buildings.

Their analysis shows if there was large-scale uptake of very high efficiency buildings, without solar generation, annual electricity demand would decrease by 30 per cent, and seasonal variation would reduce by 50 per cent in 2050. In comparison, a scenario of self-generation from solar photovoltaic (PV), without changes to current building standards, would also reduce annual electricity demand by 30 per cent, but would increase seasonal variation by 40 per cent.

If both high building standards and solar PV were combined, annual demand would decrease by 65 per cent, but seasonal variation would only reduce by 4 per cent.

“The focus, from a system wide perspective for New Zealand, should remain on improving the energy efficiency of our building stock as fast as possible rather than self-generation as we have other low-cost options for renewable electricity,” Associate Professor Jack says.

He is quick to clarify that solar PV in general is not a bad thing, but stresses how highly renewable electricity grids are heavily dependent on external factors such as seasons and weather and large-scale uptake of solar will have an important impact.

“Solar PV can be very beneficial in some regions, especially when it aligns with growing cooling demand. It can also provide increased energy resilience and electricity supply in remote regions, but it shouldn’t be prioritised above energy efficiency and/or become a requirement of future building codes nationally as is the growing trend in some countries.

“We need to think carefully about both energy supply and demand and how they match. In New Zealand, the winter peak in electricity – which is becoming harder and harder to meet with renewable supply – is largely caused by residential electrical heating.

“On the other hand, we chronically underheat our houses leading to well-documented health problems.”

Associate Professor Jack says the solution is to significantly improve our new and existing building stock to make highly efficient nearly-zero energy buildings which require very little energy for heating.

This work was funded by MBIE via a Smart Ideas programme: “Avoiding carbon lock-in: Understanding the long-term consequences of low-carbon pathways for buildings”.

Publication details

Seasonal variation in electricity demand of solar-powered net-zero energy housing in temperate climates
M.W. Jack, H.B. Konings
Energy and Buildings

For more information, contact:

Associate Professor Michael Jack
Department of Physics
University of Otago

Ellie Rowley
Communications Adviser
University of Otago
Mob +64 21 278 8200

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