Sun hours map

The sun hours map calculates how many hours of direct sun each point on the ground receives on the chosen day, and outputs it as a plate and three figures.

Overview

The «3D model» in the «Sun & shadow» section shows the shadow at one time of day. It does not say how many hours of sun a point receives over the day.

The sun hours map calculates the shadow every 10 minutes from sunrise to sunset and adds up the time in the sun at every point on the ground. The same calculation appears in the diagram set as the «Sun hours» plate (winter solstice).

How to use

1. Set the site and radius (the map calculates up to a 1,000 m radius)
2. In the «Sun & shadow» section, choose the «Sun hours map»
3. Choose the day: 21 June, 21 March, 23 September or 21 December
4. Press «Compute»
5. Save with «Save PNG» or «Save plate only»

«Save PNG» keeps the title, colour bar and note. «Save plate only» saves only the drawing; the caption is then added by hand.

Figures

The figures are for comparing places. They are not a planning criterion. The sunlight simulation is not a demonstration of compliance with DIN EN 17037 or DIN 5034-1.

Time reference

The map sums the whole day from sunrise to sunset. No time window is cut out.

The sun position is calculated in true solar time (12:00 is the moment the sun is due south). All times are standard time (CET, UTC+1) without daylight saving time. From late March to late October the clock shows one hour more: 12:00 CET is 13:00 CEST.

True noon is derived from the longitude of the site and the time zone in the header of the EPW weather file (1 for Germany), not from an estimate based on longitude. Berlin lies at 13.3° E, west of the reference meridian 15° E; true noon there falls between about 12:05 and 12:15 CET, in Cologne (7.0° E) between about 12:30 and 12:40 CET.

Method

The map uses the same building height map as wind and thermal comfort, plus the terrain. The shadow is pure geometry: no flow simulation, no GPU job.

1. For the chosen day, the sun position is calculated every 10 minutes from sunrise to sunset
2. At each step, every ground cell is classed as sunlit or shaded
3. The time in the sun is added up per cell

The difference between 10-minute and 6-minute steps is 0.01 h on average. The grid is 4 m (the same as wind and thermal comfort, so the plates can be compared). Buildings up to 400 m around the site cast shadows into the plate.

Shadow test

The grid is traversed away from the sun, carrying the highest point seen so far minus the drop over the distance (running maximum). No building between two sample points is skipped. The «Thermal comfort» section uses the same shadow function.

Computing time

If several people compute at the same time, the jobs run one after another. The same site with the same settings comes from the cache.

Display

The colour steps change at 0, 1, 2, 3, 4, 5, 6, 8, 10 and 12 hours. Up to 6 hours the steps are 1 hour wide, so places with little sun are separated by colour. Buildings are filled light grey.

Limitations

• The heights come from the LoD2 3D building models. A building built after the survey can be missing or have an estimated height; there the map can look sunnier than in reality. Buildings without a known height are missing
• The map measures sun on the ground. Windows are vertical, receive the sun at a different angle and differ by floor; the value on the ground says nothing about the rooms above
• Trees and roof overhangs are not included. Tree shade is used only in the Thermal comfort section

In the design stage the plate shows where the winter sun reaches around the site and where it does not: which open spaces are usable in winter, which ground-floor frontages stay dark, and which parts of the site lie in the shadow of neighbours all day.

Data sources

Related guides

• Sun path and shadow
• Wind
• Thermal comfort
• Building heights and terrain
• Data sources

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