How much solar energy could your home capture?

A University of Auckland researcher has created a new online tool for city residents to find out whether installing solar panels on their roof could help them make or save cash.

Last year, Dr Kiti Suomalainen Unveiled a 3D model that mapped out the best places in Auckland to harness solar energy, finding that suburbs including Botany Downs, Shelly Park, Massey and Flatbush could potentially harvest nearly 4000 kilowatt hours (kWh) each year.

She built this using Auckland Council's LiDAR data, which is collected by planes emitting light pulses and timing how long it took for the reflected pulse to return to the aircraft.

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Ultimately, the model suggested 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.

Suomalainen has since used that model to develop an online calculator that crunches the solar rooftop potential of half a million Auckland buildings down to one square metre.

This potential depended on such things as the roof's slope and aspect, and shade from surrounding buildings and trees.

The calculator allows users to zoom in on their rooftop for a colour-coded view of its solar energy potential, which highlights the best spots to place panels. Photo / Supplied
The calculator allows users to zoom in on their rooftop for a colour-coded view of its solar energy potential, which highlights the best spots to place panels. Photo / Supplied

"Solar generation is rapidly rising in New Zealand, with homes leading the trend," said Suomalainen, a research fellow at the University of Auckland Business School's Energy Centre.

"We wanted to offer an educational tool that is impartial and realistic to help people work out if solar is economic for their households or workplaces."

New Zealand's total installed solar capacity rose fivefold over the three years to 2017, and Auckland Council has a goal of 970MW installed capacity of solar photovoltaics by 2040.

The calculator allows users to zoom in on their rooftop for a colour-coded view of its solar energy potential, which highlights the best spots to place panels.

Homeowners could also enter the size and quality solar panel they prefer, how much solar power they would use and how much they would sell back to the grid, along with several other values.

The calculator, which is now at the stage where users can test it, offered the total value of the installation over its lifetime, suggesting that solar panels were a good investment if the result was positive.

"Self-consumption rate - the percentage of solar power that you use yourself, rather than sell back to the grid - is the main thing that will affect your economics," she said.

"If you're at home all day you will probably use more power than someone who is at work or school most of the day.

"For every kilowatt-hour of solar power you use, you save about 27c.

"The buy-back rate at the moment is around 8c - so the more you use, the greater the overall value of your solar generation."