Revealed: The suburbs best for solar panels

In a 3D model thought to be the first of its kind in New Zealand, a researcher has mapped the rooftop solar potential of half a million Auckland homes. Photo / Richard Robinson

Leafy suburbs like Parnell and Remuera might be seen as Auckland's elite neighbourhoods but more affordable areas have the upper hand in something, it seems.

In a 3D model thought to be the first of its kind in New Zealand, a researcher has mapped the rooftop solar potential of half a million Auckland homes, down to the precision of one square metre.

And it turns out the best spots aren't plush, inner-city suburbs but those in southeast areas.

"A lot of the leafy suburbs aren't that good for solar, because they are leafy - the trees shade the rooftops," said Dr Kiti Suomalainen, of the University of Auckland's Business School.

"Also, a lot of the older, more expensive suburbs are on hilly terrain, which can also reduce the sunlight that reaches the roofs."

Ultimately, the model suggests that if 250,000 houses had 36sq m of solar rooftop panels, they could together meet Auckland Council's "low carbon" target of powering the equivalent of 176,565 homes with the sun.

Dr Suomalainen's analysis found that some of the best-placed Auckland areas - in Botany Downs, Shelly Park, Massey and Flatbush - could potentially harvest nearly 4000 kilowatt hours (kWh) each year.

While the average Kiwi home annually consumes about 8000 kWh, Dr Suomalainen said that for well-placed solar users, the amount they could save on electricity costs would depend on their configuration.

"It will depend on the electricity price, and whether you are renting a solar panel or have bought one yourself," she said. "But generally, with the current electricity price, you tend to save money as long as you are consuming all the electricity you produce yourself."

Dr Suomalainen has worked with colleague Dr Tony Downward to examine the consequences of solar uptake on the electricity market.

They say the model could help target rooftop installation of solar panels where they would generate the most power.

Being able to accurately estimate individual houses' solar potential could also be helpful if a new dis-ruptive technology suddenly made self-generated solar power more attractive, driving a surge of consumers off the grid and leaving fewer customers to pay for the distribution network.

Dr Downward said despite a growing population there had been little growth in NZ's residential energy use since it peaked in 2010, partly due to efficiency gains from lighting and home appliances.

It might not be sensible to upgrade and maintain distribution lines as they near the end of their economic life in certain areas, he said.

"You'd need to consider the solar potential in those areas and manage the installation of rooftop solar and batteries in order to ensure an affordable and reliable distribution."

Zooming in on promising hot spots

Dr Kiti Suomalainen. Photo / Supplied

To build her model of Auckland's best solar spots, Dr Kiti Suomalainen worked on point elevation data provided by Auckland Council.

This data was collected by planes that criss-crossed the city, emitting light pulses and timing how long it took for the reflected light to return to the plane, which gave the distance from the reflected surface to the plane.

She converted it to a 3D model and overlaid it with building footprints, excluding industrial and sparsely populated areas.

Also factored in was the trajectory of the sun across the year, with compass orientation and roof slopes calculated from the 3D model, and the effect of trees, neighbouring buildings and topography.

Finally, she devised a five-point scale to indicate the solar potential by building and neighbourhood.

Dr Suomalainen intends to eventually make the rooftops results public and searchable by address.