This calculator estimates the solar energy that can be collected by a solar capture device (solar panel) at a given address, panel direction and roof slope.

Go to the SolarView tool

What does SolarView do?

SolarView gives an estimate of the available solar energy at a particular location for people considering installing a solar energy system. The program allows users to determine the amount of solar energy (insolation) that would be received at a given location based on local topography (landscape), orientation of the solar panels and other obstructions,such as buildings.

How does it do it?

The program combines an image of the local landscape with irradiance data from the nearest climate station. This is typically more than 10 years of "sunlight hours" data. You should be able to recognise the local landscape for each location entered into the system. The x-axis of the plot is in degrees bearing, i.e.west (-90°), North (0°), and east (90°). 

The 5 curves are the path of the sun on the 21 Dec (summer solstice) , 21 Jun (winter solstice), 21 Mar (autumn equinox), 21 Aug & 21 Oct  and the numbers indicate how much solar energy is available on that day.

Example of SolarView output

How do I use it?

The program determines the total amount of energy delivered by the sun to a one meter squrare (m²) surface during each day. As you follow the path of the sun from east to west (right to left) across the diagram, the time of day is labeled (below the curve), along with the cumulative energy received in kWh/m² (above the curve) up until that point.

You can calculate the the available solar energy for that date by taking the energy total at the time where the sun sets (where the sun path line crosses the horizon on the landscape image) and subtracting the total energy at the point where the sun rises (i.e. you missed out on this energy because there was a hill in the way!).

Just remember that the values indicate the amount of energy hitting the solar device - not how much of this energy would be converted into heat or electricity.

More information on how to use SolarView


More accurate results are available

This tool is meant as a guide. If you want a more accurate prediction of available solar energy, NIWA can provide this as a commercial service, including rigourous calculation of annual solar irradance and load / charge characterisation of installed solar systems. Alternatively we can provide tabulated data output of climate parameters (including direct irradiance, indirect irradiance, temperature and wind speed) for other programs to analyse. NIWA is interested in working collaboratively with companies to use this data directly in other applications.

Technical notes

The solar irradiance values as calculated represent the average amount of solar irradiance (both direct and indirect, with account for clouds) for the 30-day period centred on the given date. The values have been determined using the historic record of hourly irradiance (on a horizontal surface), compared with clear sky values in an algorithm that infers how much of the measured irradiance is direct (bright sunshine) and how much is diffuse (sky or cloud). With this information, and an assumed ground albedo, it is possible to calculate the irradiance (cosine-weighted radiant flux) on a surface tilted at any pitch and orientation.

Some diffuse energy is collected even when the sun is not within the hemisphere seen by the panel. When the sun is behind the horizon, the solar irradiance collected is only the diffuse component of solar insolation.

NIWA is continuing to refine this tool, for instance the insolation data currently refers only to the closest climate station, but we are working towards triangulating data to the three nearest climate stations.

All times are New Zealand Standard Time.

This program uses a digital elevation model of New Zealand at 100 m resolution to reconstruct the orographic horizon - hills, but not trees or buildings. The landscape image currently does not change with panel tilt and bearing, since the partial-hemispheric projection already shows the topography relative to orientation.

NIWA is providing this tool on a simple End User Licence Aggreement basis. In the current form, the results may not be used for commercial purposes.


Greta Point solar panels. [Dave Allen]