How Many KLY Does Your Hail Net Need? A Region-by-Region Guide for Apple Growers

Editor’s Note: This article is part of our Hail Netting Complete Guide. Visit the Hub for the full breakdown of hail protection — net types, colours, structures, installation and cost.

Quick answer: KLY is the total solar energy your orchard receives in a year. The KLY a hail net must withstand is roughly your region’s annual KLY multiplied by the years you want it to last, plus a margin. Central Chile, South Africa’s Ceres valley and Queensland’s Granite Belt get 150–175 KLY a year — so a net meant to last 10 years there needs to withstand 1,500 KLY or more.

A net that “died early” is rarely a bad net. Far more often it’s a net rated for European sun, strung up under a Chilean or South African sky. The label said 700 KLY. The orchard receives 160 KLY every year. Nobody did the arithmetic.

This guide gives you that arithmetic — with measured sunshine for 14 apple regions — plus the four things that make a net age faster than its KLY number predicts.

What KLY actually measures (and why most suppliers explain it wrong)

KLY — kilolangley — measures the total solar energy that falls on one square metre in a year. One KLY equals 41.84 MJ/m², or about 11.62 kWh/m². Despite how it’s usually described, the figure the netting industry uses is total sunshine across all wavelengths, not UV alone.

Most supplier pages — including an older article of ours — call KLY “UV energy.” The numbers they quote tell a different story. European net makers say the Netherlands receives 80–100 KLY a year ^[1][2]. Satellite data puts Dutch total solar radiation at about 91 KLY ^[3]. UV alone is only a small fraction of that.

Why it matters: if you compare a supplier’s KLY rating against a UV figure, you’ll underestimate your sun by a wide margin and buy the wrong net.

For the basics of the unit itself, see our KLY explainer.

How to work out the KLY your net must withstand — in three steps

Multiply your orchard’s annual KLY by the years you want the net to last, then add a margin for sprays, net colour, altitude and wind. The result is the KLY your net should be rated to withstand.

Step 1 — Find your annual KLY. Look up your orchard’s global horizontal irradiation (GHI) in kWh/m² per year on the World Bank’s free Global Solar Atlas, then divide by 11.62. Or use the table below.

Step 2 — Multiply by the years you want. A 10-year net in a 150-KLY orchard must withstand 1,500 KLY.

Step 3 — Add a margin. See the four ageing factors further down. If more than one applies to you, the margin matters more than the headline number.

One definition to settle before you compare quotes: in the netting trade, a net’s life usually ends when it has lost half its original tensile strength ^[1]. Ask every supplier whether their KLY rating and warranty use the same 50% line.

Annual sunshine in 14 apple regions — and the KLY your net needs

Southern-hemisphere apple regions receive roughly 130–175 KLY a year — 40–90% more than Western Europe. A net sized for the Netherlands will age that much faster in Chile, South Africa or Queensland.

Annual KLY = long-term average GHI from the Global Solar Atlas (World Bank / Solargis) ÷ 11.62, cross-checked against NASA POWER 2001–2020 data ^[3][4]. “KLY for 8 / 10 years” is before any margin.

Two things stand out. First, the gap between Europe and the Southern Hemisphere is large enough to cut a net’s life nearly in half. Second, altitude alone doesn’t decide it: Srinagar at 1,587 m sits in the same band as Elgin at 280 m.

Your KLY figure is only the first filter. Structure, wind load and net colour decide the rest — compare constructions, specifications and warranty options before you choose.

Compare hail net options →

Four things that make a net age faster than its KLY predicts

KLY sets the baseline. Four conditions push real-world ageing beyond it: sulfur and chlorine sprays, heat, mechanical stress, and the net’s colour. High altitude adds a fifth, smaller effect.

1. Sulfur and chlorine sprays. The UV stabilisers in most nets belong to a family called HALS. Sulfur- and chlorine-based sprays are acidic and can deactivate them; chlorine also attacks the polymer directly. The damage is worse in hot, poorly ventilated conditions ^[5][6]. If you spray sulfur regularly, add a generous margin and ask your supplier which stabiliser they use.

2. Heat. Nets age faster where they sit against hot surfaces such as metal structures ^[5].

3. Wind and mechanical stress. A net under constant tension or flogging in the wind loses strength faster than the sunshine alone would predict. One Dutch supplier reports that its clear hail nets rarely reach their full UV life because wind load wears them out first ^[2].

4. Colour. Carbon black blocks UV physically, so black nets withstand more. One European supplier rates its clear hail net at 950 KLY and its black net at 1,400 KLY ^[2]. Clear and white nets let more light through for fruit colour — see our guide to choosing a hail net colour — but you pay for it in UV life.

Altitude. Measured sunshine data already includes the effect of altitude, so don’t add a separate altitude factor to the KLY figure. But UV rises about 10% for every 1,000 m ^[7], and UV is the part that ages plastic. For orchards above 1,500 m, add a little extra margin.

Three questions to ask any supplier about KLY

A KLY figure on a spec sheet only helps if you can compare it with your own sun and know what “end of life” means. Three questions get you most of the way.

1. Is your KLY figure total solar energy or UV only? It should be total solar energy, so you can compare it with your region’s figure.
2. What counts as end of life? 50% of original tensile strength is the common line.
3. How does the warranty map to the KLY? A warranty longer than your annual sunshine can support is a red flag.

Be wary of anyone who converts lab hours straight into field years — there is no single conversion that holds across climates, sprays and wind. We explain why in what accelerated UV tests can and can’t tell you. For a fuller checklist, see how to verify a supplier’s UV claims.

How we rate our hail nets

Every EyouAgro hail net carries a KLY figure: our assessment of how much sunshine it can take before losing half its strength, based on our own weathering tests and three decades of field feedback. Our Leno nets are rated to 700–1,500 KLY with 8 to 10+ year UV warranties; our heavy-duty Raschel nets to 1,200 KLY with 8-year warranties.

Match the table to your region. In Chile or South Africa, a 10-year net means our 1,500-KLY Leno range. In Hawke’s Bay or South Tyrol, a 1,200-KLY Raschel will cover eight seasons with margin.

Planning a wholesale orchard project? Tell us your orchard’s location, the area you need to cover and how long you want the net to last. We’ll recommend a suitable construction and send you the specification sheet and warranty terms. If you already know your block sizes, our hail netting calculator helps you estimate quantities first.

Request a KLY-matched spec sheet →

Wholesale projects only · MOQ 20,000 m² · Lead time 60+ days

Frequently Asked Questions

What is the difference between KLY and the UV Index?

The UV Index measures how strong UV is at one moment. KLY measures the total solar energy an area receives over a whole year. A net fails from the cumulative dose, not from one hot afternoon, so KLY is the figure used to size netting.

Do clear and black hail nets last the same at the same KLY?

If both are rated to the same KLY, they should reach end of life at a similar dose. In practice black nets can be rated higher because carbon black blocks UV, while clear nets are often limited by wind wear before they reach their UV limit.

How much margin should I add if I spray sulfur?

There is no published formula. Sulfur- and chlorine-based sprays can deactivate common UV stabilisers, so add a generous margin — and ask your supplier which stabiliser the net uses before you buy.

Do I need extra KLY at high altitude?

Measured sunshine data for your site already includes altitude, so use it directly. Because UV rises about 10% per 1,000 m, add a small extra margin for orchards above 1,500 m.

How do I find my orchard’s annual KLY?

Look up your orchard’s annual GHI in kWh/m² on the free Global Solar Atlas and divide by 11.62. The table above covers 14 major apple regions.

How can I tell a hail net is reaching the end of its life?

Watch for a chalky surface, stiffness, and threads that snap when you flex them. By then the net has usually lost most of its strength and a hailstorm can tear it.

References

1. Duranet. The effect of solar radiation on plastic nets and tarpaulins. duranet.com
2. FruitSecurity Holland. UV resistance and Damage to hail nets: what every fruit grower must know. fruitsecurityholland.com · fruitsecurityholland.com
3. World Bank / Solargis. Global Solar Atlas, long-term average GHI. globalsolaratlas.info
4. NASA Langley Research Center. POWER Project, climatology 2001–2020. power.larc.nasa.gov
5. BASF. Agriculture — light stabilizers for agricultural films (2016).
6. Clariant. Hostavin NOW — pesticide-resistant light stabilizer. clariant.com
7. World Health Organization. Radiation: Ultraviolet (UV) — Q&A. who.int

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