Winter sun hours on any New Zealand section

Who uses this

• Buyers. Check winter sun on a section before an open home in summer fools them.
• Architects. Place living areas, decks and glazing where the winter sun actually reaches.
• Growers and solar installers. Find the ground that stays lit in June.

When to use it

• Checking winter sun on a house site, a deck or a garden before you buy or build.
• Comparing sunny and shaded parts of a block for planting or stock.
• Seeing when the sun first reaches a valley floor and when it leaves.

Which tool for your job

Sunlight is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.

How to use it

1. Select a property, draw an area or upload a boundary.
2. Pick a date: the shortest day, an equinox, the longest day, or any date you type.
3. Choose bare ground, or the LiDAR surface so trees and buildings cast shadows too.
4. Run. Read total hours, first and last sun, and step through the day half an hour at a time to watch the shadows move.
5. Download the sun-hours grid as a GeoTIFF in NZTM2000 for GIS. Downloading needs a pass.

Step by step: Mt Iron, Wānaka

We model the shortest day, 21 June, across Mt Iron and the houses on its eastern side.

What it showed

• North faces with an open horizon get the most winter sun; the south-west flank sits in the hill's own shadow for much of the day.
• Switch on trees and buildings, where LiDAR has been flown, to include the shade from shelterbelts and neighbours.

Screenshots from NZ Elevation Tools. Aerial imagery from LINZ Basemaps. Sourced from the LINZ Data Service and licensed by Environment Southland, Otago Regional Council and Queenstown-Lakes District Council for re-use under the Creative Commons Attribution 4.0 International licence.

How it works

The sun's position is computed for the chosen date every 15 minutes. At each step the tool casts shadows across the whole grid from the sun's direction, including terrain up to 3 km away. A cell is lit for that step when no shadow falls on it and its own slope faces the sun.

Hours of sun are the count of lit steps. With the surface option the LiDAR surface model, which includes canopy and roofs, is used as the blocking surface instead of bare ground.

Reading the results

Winter (21 June) is the test that matters for a house site. A north-facing slope with an open northern horizon will show the most hours.

First and last sun are the clock times the sun first reaches any part of the area and last leaves it.

Limits and warnings

• Direct sun only. Cloud, haze and diffuse light are not modelled.
• Shadows from things further than 3 km away, such as a distant range, are ignored. In deep valleys the true horizon may be further out.
• The surface model is only available where LiDAR has been flown, and shows trees as they were on the capture date.

Compare quotes without ringing around

Sunlight gives you a fast, indicative answer. When the job needs pricing, designing or signing off, getting quotes usually means calling around and explaining the same site over and over. Instead, run the tool on your site and choose Compare quotes under the result. Describe the job once and we’ll send it to up to 3 local solar installers, with an aerial map of the site, a Google Earth file and your results attached, so they can price it properly from the start. They quote you directly. It’s free and there’s no obligation.

Data and attribution

Heights come from the LINZ elevation tiles: LINZ’s national bare-earth elevation model (LiDAR where it has been flown, the 8 m model elsewhere), stored in 0.1 m steps, read in your browser at the finest zoom that fits the area (cells of about 0.5 m on a small area, coarser on a larger one), with the ground up to 3 km beyond it read at much coarser cells (about 15 m) for distant shadows. With the surface option, the matching LINZ surface tiles (the LiDAR surface model, with trees and buildings) are read at the same cell size so trees and buildings in the area cast shadows. Over the sea the tiles read 0 m; they hold no seabed.

Elevation and cadastral data is sourced from the LINZ Data Service and licensed for re-use under the Creative Commons Attribution 4.0 International licence. Copyright in each LiDAR survey belongs to the body that commissioned it — a regional or district council, Waka Kotahi, NIWA and around thirty others — rather than to LINZ, which hosts and processes the national dataset. Every file exported from this site names the licensors whose surveys cover the area, and anything you publish from those files carries the same attribution requirement. See https://www.linz.govt.nz/products-services/data/licensing-and-using-data/attributing-elevation-or-aerial-imagery-data

Questions

Related

Neighbouring tools

• Find Matching Areas — Combines several tests at once (slope, facing direction, winter sun, wetness and room to build) and highlights only the ground that passes them all, so the next tool can run on just that patch.
• Slope & Aspect — Maps how steep every part of your area is and which compass direction each face points, with a full breakdown of slope classes and aspect shares.
• Viewshed — Shows which ground within 1 to 10 km can be seen from a point, for a chosen eye height, with earth curvature and refraction allowed for and, optionally, trees and buildings blocking the view.