South Africa Wine Technical Yearbook 2025

for comparing row directions. You just type in your location (start with the nearest town, then zoom to your vineyard), leave most settings as they are, and tweak two key things: the tilt (90 degrees for a VSP) and the azimuth heading (the angle, clockwise from true north, that your rows are orientated). Below is a table showing how azimuth ties to row direction – and which rows get slammed with the most hourly sunlight.

water stress and canopy details among the many factors to the viticulturists – those can be tweaked. Is solar energy hitting the grapes? That’s harder to dodge. Here’s a fun way to think about it: a perfect VSP (vertical shoot-positioned) trellised vineyard is like a solar panel standing upright, soaking up the sun on both sides to produce sugar instead of electricity. That sparked an idea. I jumped onto the free PVWatts ® Calculator online, a tool for sizing up solar panels. It turned out to be an excellent fit

TABLE 1. The maximum hourly amount of solar energy in different row directions received on the morning and afternoon side of the canopy on the 1 January with the help of the PVWatts Calculator.

Maximum sun exposure

Offset angle from optimal drainage

Heading of sun

Azimuth angle Option

Row direction

Shadow length at an object of 1,1 m

Plane of array irradiance (W/m 2 )

NE

45°

Option 2 NW-SE

9:00 9:00

1,34 m 1,34 m 2,16 m 2,16 m 0,66 m 0,66 m 1,03 m 1,03 m

631.63 773.08 829.53 702.31 768.78 896.51 812.88 646.10

40

E-NE

67.5 Option 4 NNW-SSE

17.5 27.5

Morning sun

E-SE 112.5 Option 1 NNE-SSW 8:00

SE

135°

Option 3 NE-SW 8:00

50 40

SW 225°

Option 2 NW-SE

15:00 15:00

W-SW 247.5 Option 4 NNW-SSE

17.5 27.5

Afternoon sun

W-NW 292.5 Option 1 NNE-SSW 16:00

NW 315°

Option 3 NE-SW 15:00

50

the top foliage wire) to the northwest. In NW-SE rows, the wind blows along the rows, and the canopy “fringe” lines up with the row direction, leaving grapes more exposed. But in NNE-SSW rows, the “fringe” shoots sprawl across the afternoon sun side, casting a shadow that shields the grapes on the opposite rows from the harshest rays. The maximum morning sun exposure for NNE-SSW (08:00) will also be limited if the row width is less than 2,16 m, caused by the low angle of the sun and the shadow that will be cast by a 1,1 m-high canopy in relation to the grapes. The SunCalc.org website was used to determine the shadow length. So, there you have it – science, soil, sun and a bit of wind all mixed into one decision. NNE-SSW feels like the sweet spot for this block. Now, I’m ready for that debate! 

The results? The best drainage direction (NNW-SSE, option 4) also gets the most afternoon sun, but this is bad news for sunburn. The NE-SW (option 3) direction receives the least sun, but is terrible for drainage. Knowing how much these soils are prone to stagnant water, I could only stomach two options: NNE-SSW (option 1) or NNW-SSE (option 4). NNE-SSW (option 1) edged out as my pick – it’s a bit cooler and more balanced across the block. Then there’s the wind. Summer here is synonymous with a strong southeast breeze, especially in the afternoons. I chatted with the farm’s seasoned viticulturist while we stood in the vineyard, and he dropped some wisdom: the NNE-SSW (option 1) rows on the farm have less sunburn than the NW-SE (option 2) ones. Why? That southeasterly wind bends the top part of the canopy (free-hanging above

For more information, contact Heinrich Schloms at heinrich@vinpro.co.za. Reference https://www.wineland.co.za/watts-up-with-row-direction/

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TECHNICAL YEARBOOK 2025