Let the sun shine: Auckland’s rooftop solar potential

Ever wondered how much power you could generate from the sunlight hitting your roof? New geographical 3D computer modelling by a researcher at the University of Auckland Business School gives the solar rooftop potential of half a million Auckland homes – down to one square metre.

And it turns out the top 20 places for solar are mostly cheap-to-mid-range neighbourhoods. The top three are in Southeast Auckland, around Botany Downs [SEE LIST BELOW]

“A lot of the leafy suburbs aren’t that good for solar, because they are leafy – the trees shade the rooftops,” says model devisor Dr Kiti Suomalainen.

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

The modelling is thought to be the first of its kind in New Zealand. It suggests that if 250,000 houses had 36 sqm of solar rooftop panels, they could together meet Auckland Council’s “low carbon” target of powering the equivalent of 176,565 homes with solar energy.

Dr Suomalainen has worked with Engineering lecturer 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 help avert the feared “death spiral” that happens when a new, so-called disruptive technology threatens to cannibalise the market for an existing technology, undermining its viability.

“A ‘death spiral’ occurs when customers start switching to solar and disconnect from the main power grid, leaving fewer and fewer customers to pay for the distribution network,” explains Dr Downward.

“This can lead to increased power prices, making solar power more attractive, eroding the value of existing infrastructure – the distribution lines and so on - and finally leading to ‘stranded assets’, he says.

“In a year when the hydro lakes are full, 75-80 percent of our electricity is already is renewable. After the country’s last coal plant shuts down in 2018, there’ll not be much non-renewable energy left in the electricity system.

“You don’t want to build in solar in a way that will offset existing generation technologies that are already renewable.

“This tool could help selectively promote the installation of solar in certain areas in order to reduce our reliance on non-renewable thermal plants.”

Dr Downward points out that residential energy use across the country peaked in 2010 and has had little growth in recent years, despite a growing population; this has been in part due to efficiency gains from home appliances and lighting.

“Over time, it may be that it’s not sensible to be upgrading and maintaining distribution lines as they approach the end of their economic life in certain areas. But in order to make that decision," he says, "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 network for all customers."

To build her model, Dr 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 this to a 3D model and overlaid it with building footprints, then excluded heavily industrial and sparsely populated areas.

She then used the trajectory of the sun through the sky across the year, the compass orientation and roof slopes calculated from the 3D model, to calculate the annual solar radiation on each point on the roof, factoring in the effect of trees, neighbouring buildings and topography. Finally, she devised a five-point scale to indicate the solar potential by individual building, and by neighbourhood.

Dr Suomalainen says she intends to eventually make this rooftops results public and searchable by address.

Dr Suomalainen and Dr Downward will give a talk about the model and its potential uses on Wednesday 30 April at the Business School, from 6pm.

LIST of Top 20 Auckland Suburbs for Solar Potential (1=poor [<1100 kWh/m2], 5=excellent [1400-1500 kWh/m2]; by the best 36 sqm of each building; by census area units)
Kilkenny (Shelley Park/Sommerville) 3.92
Maungamaungaroa (Shelly Park/Cockle Bay) 3.90
Millhouse (Botany Downs) 3.89
Westgate (Massey) 3.84
Point View (Flatbush/Dannemora) 3.84
Windsor Park 3.83
Donegal Park (Flatbush) 3.80
Dannemora 3.80
North Harbour 3.79
Pinehill 3.79
Totara Heights 3.77
Fairview 3.76
Burswood 3.76
Pukekohe West 3.75
Sturges North 3.74
Lucken Point 3.74
Half Moon Bay 3.73
Golfland 3.72
Unsworth Heights 3.72
Pigeon Mountain South 3.71

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