Solutions: Outlook for sunshine

Solar generation is tipped to play an increasingly important part in meeting New Zealand's future electricity needs.

A recent report commissioned by the Ministry for Economic Development (now the Ministry of Business, Innovation Employment) highlights the potential of underutilised renewable energy sources – like solar – to ensure a sustainable supply for the country, even as demand burgeons out to 2040.

"Solar radiation is an abundant, free, non-polluting and renewable energy source," says NIWA Atmospheric Physicist Ben Liley. "In New Zealand, many homes are exposed to 20 to 30 times more energy from the sun annually than they use in electricity or gas, but little use is made of it. A well-designed home can capture the sun's heat directly, and a properly installed and controlled solar water heating system will meet 50 to 75 per cent of your hot water needs every year."

You may have considered having installing solar panels fitted to your home, but just how much solar energy is available in your region to power your life and livelihood? Will your lights stay bright through seasonal fluctuations in the strength and duration of sunlight? Are your solar panels oriented correctly? What if someone builds a high-rise next door, casting them into the shade?

NIWA's SolarView, a free online tool, answers your questions in an instant. SolarView estimates the average amount of solar energy (insolation) available to power a one-square-metre solar panel at any location in New Zealand, at different times of the day and year.

Find out more about SolarView

Simply enter your street address, or click a location on the embedded Google Maps link, and then specify the tilt and bearing of your roof, or panel-bearing surface. SolarView takes these inputs, factors in surrounding terrain, then taps into NIWA's extensive climate database to accurately depict the sun's path from sunrise to sunset at five representative dates during the year, including summer and winter extremes. It also plots hourly measurements of cumulative insolation in kilowatt hours (kWh) per square metre on each path.

SolarView offers guidance on how to plot nearby obstructions, like buildings and trees, onto the profile, and calculate any diminishing effect of their shade on your kilowatts. Any homeowner or solar energy specialist can use this information to determine how much money solar panels or a solar water heating system might save them.

The tool also helps precisely determine the optimum location for panels on any roof, given the unique surroundings and situation of each home.

SolarView is Liley's brainchild: he designed the software to help people considering installing a solar energy system. "The idea is to help users appreciate how much solar energy is available, and how it depends on various parameters," he says. "To make solar power work for them, it's important that people have good information specific to their situation. It's also important that they can make sense of that information, so we've provided guidelines on how to put SolarView's calculations into perspective."

On average, New Zealand receives about 2000 hours of bright sunshine each year. In energy terms, that corresponds to about four kWh per square metre of a horizontal surface every day. To put that into perspective, says Liley: "For an average New Zealand home, a three-kW solar photovoltaic (PV) array should generate more than half the electricity used in that house over a year. Instead of all the batteries you used to need – for when there was too little light to generate – grid-connected systems are now the norm."

Liley says SolarView is also popular with homebuyers wanting to find out how much sun their prospective new property will receive, checking sun angles at different times of year.

"The tool is a very useful guide," he says. "And if users need more detailed records – or a prediction of available solar energy – NIWA can provide this as a commercial service. We can also supply tabulated data on climate parameters, including direct irradiance, indirect irradiance, temperature and wind speed, for input into other programmes which can then analyse solar systems or a whole building's energy performance.


Atmospheric Scientist