Assessing Complementarity for Wind and Solar Energy in New Zealand

In recent years, there has been an increase in intermittent renewable energy sources (RES) in power system electricity mixes, leading to extensive research on quantifying the intermittency of primarily wind turbine generation (WTG) and solar PV generation and proposing mitigation strategies. Amongst other impacts that these fluctuations have on a traditional power grid, System Operators (SO) face the challenge of accurately predicting generation patterns across various time intervals. Studies conducted in other countries have explored different methods to minimize the impacts of intermittent generation, such as employing storage devices, smart grids, and geographical diversity based on generation complementarity. Generation complementarity refers to the negative correlation between different types of generation, which effectively smooths out intermittencies. For countries like New Zealand, with substantial potential for WTG and solar PV generation, investigating complementarity is crucial for system operators, plant owners, and investors. Previous generation correlation studies conducted in New Zealand did not include solar data until recently, so this study investigates the prospect of utilizing temporal (multiple RES in one location), spatial (one RES in multiple locations) and spatio-temporal (multiple RES in multiple locations) complementarity in New Zealand. The study utilizes 5 years’ worth of hourly observational data from local meteorological services and real power outputs of operating wind farms. The typical pre-processing steps were applied to data after which Spearman’s Rank Correlation (SRC), Cross-correlation and Canonical Correlation (CCA) analyses were applied to the modelled power data and derived datasets to determine complementarity. The site with the highest modelled solar PV power is located at the top of the South Island, while Northland, Bay of Plenty, and Hawkes Bay also demonstrate high solar PV generation. The modelled WTGs operate above 50% of their capacity for approximately 12% of the period while solar PV generation remains below 40% of its modelled capacity for 99% of the time. Among the operating wind farms, generators in the North Island operate at a higher percentage of their capacity compared to those on the South Island, particularly during the middle of summer, spring, and autumn.

Although the temporal complementarity analysis does not identify significant complementarity, there is a higher likelihood of exhibiting complementary characteristics during colder months and the time window between 12 pm and 2 pm daily. Spatial complementarity analysis results follow a similar trend as observed in studies conducted in other countries but the correlation coefficients in this study are also influenced by its proximity to the coast and the degree of exposure or sheltering from sea winds even at considerable separation distances. The spatio-temporal complementarity analysis reveals a dependence on seasonal cycles. The most optimal spatio-temporal complementary pairs exhibit higher coefficients during transitional months, suggesting that their complementary relationship is most prominent during the shift from one primary season to another. The study reveals the need for further work to be done in this research area particularly for New Zealand. This will require contributions from multi-disciplines to reveal reliable studies that investigate the effects of weather variables on the evolving power system.