Are solar panels a good investment? Auckland Uni answers

Researchers at The University of Auckland are helping Kiwi businesses answer a burning question: Are solar panels an economic option for my building?

A new tool from the University will help Auckland businesses and households work out whether it makes financial sense to install solar panels on their roofs.

The calculator is completely free, and accessible online. The user selects a building from a digital map and can zoom in on their rooftop for a colour-coded view of its solar energy potential, which highlights the best spots to place panels.

Users can 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.

The calculator gives the total value (savings and revenues minus costs) of the installation over its lifetime. If it is positive, it's a good investment.

In addition, the tool calculates the "solar rooftop potential" based on a number of factors, including the roof's slope and aspect, and shade from surrounding buildings and trees.

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

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

Suomalainen devised the geographical 3D computer modelling behind the calculator.

She used LiDAR data from Auckland Council, which is collected by planes emitting light pulses and timing how long it took for the reflected pulse to return to the plane, to construct a digital 3D model of the city with all its buildings and trees and other objects. With this, the solar radiation on individual rooftops could be calculated.

"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," adds Suomalainen.

"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 adds.

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

The calculator is now at a stage where users can test it and report any issues, such as mismatch of solar potential and underlying building on the map due to outdated building data, and any feedback is welcomed.

You can view the calculator and read more about the project here.