NZ's solar resource is better than that of Japan or southern France. File photo: Getty Images

Victoria University of Wellington’s Alan Brent looks at how New Zealand’s solar resources can be used more effectively to address energy demand in our transitioning economy

Tucked in the southwest corner of Germany and surrounded with hills of the Black Forest, the city of Freiburg is well known as an innovative pioneer of green living on a large scale.

It has a goal of achieving carbon neutrality for the entire city by 2035, which will require multiple interventions, including a 100 percent reliance on renewable energy resources. But it is not only about supplying its own energy needs. Renewable energy companies have made the city their home to research and build products that are shipped worldwide.

To this end, Freiburg was home to the Solar Summit 2013, where new solar technologies were featured, and brought together investors, scientists, utility executives, and officials from various governments, among others.

Subsequently, it is now referred to as the ‘solar city’ of Europe, having installed more solar photovoltaic (PV) systems than other cities and even regions on the continent; the Fraunhofer Institute for Solar Energy Systems provides some recent facts about photovoltaics in Germany. The neighbourhood of Vauban, in particular, demonstrates the practicability of plus-energy buildings that run on solar PV and solar thermal and generate more renewable energy than the buildings and their occupants consume.

Freiburg is referred to as the ‘solar city’ of Europe. Photo: Andrewglaser at English Wikipedia [CC BY-SA 3.0] via Wikimedia Commons

Why is this important to New Zealand? Freiburg is in one of Germany’s sunniest regions, but a quick visit to the Global Solar Atlas shows that, annually, it receives around 1,200 kWh per square metre of solar radiance, which is similar to Invercargill. Indeed, at nearly 48° north, Freiburg is further from the equator than all of New Zealand. Despite this, it has developed a strong solar business and culture with lessons to be learned.

So how good is the solar resource in New Zealand? In 2010, mean annual solar radiation data were captured in the Land Resource Information Systems (LRIS) portal, and since then NIWA has provided good insights of the resource, spatially and temporally, through its SolarView tool. Further advances in satellite-modelled data prompted a revisit of the resource across the country with the development of a more detailed solar atlas of New Zealand, an initiative of Te Herenga Waka—Victoria University of Wellington in collaboration with Solargis, the service provider the World Bank Group commissioned to develop the Global Solar Atlas. The solar resource, solar PV power potential, and other parameters are provided in the form of gridded data that can be used for visualisation, further processing and geo-analysis.

To put it into perspective, our solar resource is, in general, better than that of Japan or southern France, regions with significant uptake of solar technologies. It is then not surprising we have also seen growth in the uptake of PV systems over the past five years, although from a low base, with an increase of just under 30 percent in 2018 and 2019 to a total installed capacity of nearly 130 MW.

Source: Electricity Authority

The residential sector has been the key driver for solar PV installations, accounting for over 70 percent of installed capacity at the end of 2019. The rate of solar uptake by other market segments – small and medium enterprises, commercial and industrial – increased at an even higher or similar rate to residential use, but from a much lower base.

At a utility scale, a number of solar farm projects are at different stages of development across the country. And the University of Waikato, back in 2007, highlighted the benefit of using solar thermal energy for processing in the dairy industry, given that, again, the solar resource in the Waikato region (above 1400 kWh/m2 from the solar atlas) is significantly higher than corresponding dairy production regions in Germany (around 1150 kWh/m2), and milk production and the annual solar radiation profile exhibit a degree of correlation.

However, we need to be cleverer about using our agricultural land and water resources, and therefore agro- and aqua-PV need more attention here, similar to what Fraunhofer is investigating in Germany, South, and elsewhere.

What is surprising is the good resource in our lake regions, especially on the South Island. This indicates the potential opportunity associated with adding floating PV capacity to hydropower sites that can be flexibly operated.

Investigations of these and other opportunities for how the solar resource of New Zealand can be used more effectively to address energy demand profiles in our transitioning economy are ongoing.

Professor Alan Brent is the Chair in Sustainable Energy Systems in the School of Engineering and Computer Science at Te Herenga Waka Victoria University of Wellington.

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