Build better houses to solve dry year energy problem Greater efficiency far more effective than expanding PV

18 March 2024 by Jason Quinn

Newsflash: using less energy is better than generating more of it. I know that seems obvious given the cost of new electricity generation schemes but it’s even more significantly beneficial to reduce peak heating demand because of New Zealand’s big dry winter problem.

The University of Otago’s energy programme is producing valuable work, and its latest paper by Michael Jack and Hannah Konings explains how. 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.

This would make New Zealand’s dry winter problem even more acute, especially in light of the cancellation of the New Zealand Battery Project. That ambitious project was all about storing the energy generated in summer so that it could fuel winter shortfalls. Shelving it makes it even more critical to reduce winter electricity demand. The need for winter heating drives a lot of that winter electricity peak, as we wrote about in 2021.

Seasonal storage of electricity is hard and expensive. We are much better off in New Zealand to focus really hard on reducing winter heating demand in homes—our winter peak in electrical demand is mostly residential electrical heating, even as our ‘put another jersey on’ culture lingers. Designing far more energy-efficient homes may see a slight risk in the need for active cooling, but it’s still a win. After all, cooling demand peaks exactly coincide with optimum distributed PV energy generation periods.

The paper is open access: below are the details and the abstract. There’s also a reader-friendly summary in the university’s media release and a version of that information published by the Otago Daily Times.

M.W. Jack, H.B. Konings, “Seasonal variation in electricity demand of solar-powered net-zero energy housing in temperate climates,” Energy and Buildings, Volume 303, 2024, 113826, ISSN 0378-7788,

Abstract: Net-zero energy buildings produce enough renewable energy to meet their own annual energy requirements and have been proposed as an important method of reducing operational greenhouse gas emissions in the building sector. However, self-generation via building-integrated solar PV in cold and temperate climates is anti-correlated with increasingly-electrified heating demand and could increase seasonal variability in net electricity demand to the point that it poses challenges for future electricity systems. In this paper we explore scenarios of future large-scale uptake of electrically-heated, solar-PV net-zero energy residential buildings in New Zealand and quantify the seasonal variation of the resulting net electricity demand. A scenario of large-scale uptake of very high efficiency buildings leads to reductions in annual demand of −30% and seasonal variation of −50% in 2050 compared to a base case of current building standards. In comparison, a scenario with self-generation via solar PV without changes to the building standard reduces annual demand by −30% but increases seasonal variation by +40%. In a scenario where very high building standards are combined with solar PV, annual demand decreases by −65% and seasonal variation by only −4%. From a policy perspective, whether large-scale solar PV self-generation should be supported (in addition to very-high efficiency buildings) depends on an economic trade-off between the value of distributed solar generation (including any carbon emission reductions) vs the electricity system cost of seasonal variation. For New Zealand, given the low cost of renewable electricity from a variety of alternative sources, scenarios of large-scale uptake of solar-powered net-zero energy buildings are not favourable from an electricity system perspective.

Keywords: Net-zero energy buildings; 100% renewable energy systems; Seasonal supply-demand mismatch; Energy efficient buildings


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