Storms and Extremes: The Risk That Is Not About Yield

A different kind of risk

The six variables before this one all changed a number: how many kilowatt-hours a panel makes in a normal year. Storms change a different number: the probability that the panel, the racking or the inverter is damaged or destroyed. That risk does not belong in a yield estimate, because it is episodic and skewed, a small annual chance of a large one-off loss rather than a steady drag on output. It belongs in two other places instead: the structural specification of the mount, and the insurance and maintenance reserve. This report reads the four perils that govern it, and the honest headline is how unevenly they fall.

The single most damaging peril for a photovoltaic module is large hail, because a stone of two centimetres or more can crack the glass and the cells beneath it outright. It is also the most concentrated:

The 10 of 40 markets with a defensible large-hail figure. Thirty markets are blank, not zero: almost no city publishes a days-per-year count for hail at or above 2 cm, so a number is entered only where a credible city-scale figure exists, and an explicit 0 marks a genuinely hail-exempt site. Bogota and Seoul counts include all hail sizes, not strictly >=2 cm, and are flagged as such. Full sourcing and averaging bases in the public dataset.

Two markets carry a genuinely high hail hazard, and they are the spine of this report. Johannesburg sits on the South African Highveld, one of the most hail-prone places on Earth, with roughly five damaging-hail days a year and, in the wider all-size count, more than sixty. Sydney records about five damaging-hail days a year in the city and far more across its basin, and the April 1999 storm, with nine-centimetre stones, remains Australia's costliest natural disaster; its hail-prone days are rising at roughly ten percent a decade. In these two markets the mounting and the insurance reserve should assume glass-breaking impacts, and a hail-durability rating on the module is not a luxury.

Where the danger is, and where it simply is not

Hail is only one of four perils, and across the full 40 markets the thing that governs asset survival varies enormously:

Three patterns matter for a buyer. First, the cyclone coasts are specific and severe: Tokyo and Shanghai sit on the world's most active typhoon coastline, and their structures must be cyclone-rated and, ideally, stow-capable if tracked; Seoul and New York take the occasional storm, with New York's major-hurricane recurrence around one in seventy-four years. Second, one high-latitude market breaks the intuition that cold means calm: Reykjavik has no hail and no cyclone, yet Europe's highest design wind, up to 46 metres per second on the exposed coast, so its racking is wind-governed and needs to be stronger than its benign-looking climate suggests. Third, and most useful commercially, the exempt zone is real: Antofagasta on the Atacama, along with Madrid, Athens, Santiago and Casablanca, faces no material extreme-weather peril, which is a signal not to over-specify the mount and pay for resilience the sky will never test.

The design-wind numbers carry one essential caveat, and the dataset preserves it: the averaging basis is decisive. Tokyo's code figure of 34 metres per second is a ten-minute mean, which corresponds to roughly a 56 metre-per-second three-second gust, and cannot be compared with Sydney's 45 metres per second, which is already a gust, without converting first. Eight markets carry no confirmed code wind speed at all and are left blank rather than filled with a guess.

What a buyer should actually do

Asset survival turns into three concrete decisions. Specify the mount to the real peril, not a generic one: cyclone-rated and stow-capable structures on the typhoon coasts and the high-wind outliers like Reykjavik, and a hail-durability rating on the module in Johannesburg and Sydney, but no premium for resilience in the five exempt markets. Price the insurance and the reserve to the hazard rather than the yield, because a market can be superb for production and still carry an elevated premium: the annual chance of a large loss, not the annual kilowatt-hours, sets that number. And read the trend, because two of the perils here are moving: hail-prone days are rising in Sydney and Perth even as total hail declines on the Tibetan Plateau, and the same warming that this series began with is redistributing where the damaging storms fall. A twenty-five-year asset is a twenty-five-year bet on the storms as much as on the sun.

Method and limits

This pillar records hazard, not annualised loss, because storm damage is episodic and averaging it into a percentage would misrepresent it. Hail is assessed at the two-centimetre threshold that damages photovoltaic glass; tropical-cyclone exposure is graded from basin geography and hazard screening; design wind speed is taken from the local building code with its averaging basis (three-second gust or ten-minute mean) preserved; and flood is the higher of riverine and urban screening. Four honest limits. Large-hail days are blank for 30 of the 40 markets, because almost no city publishes the figure, and a blank marks the absence of a credible number rather than an absence of hail. Return periods and several wind speeds are approximate bands inferred from hazard ratings and basin climatology rather than single published values, and each such cell says so. The dominant-peril and insurance-signal fields are a reasoned synthesis across the four hazards, not a single sourced measurement. And coastal storm surge, the dominant flood mechanism for a market like New York, is noted but out of scope for a pillar keyed to the panel and its mount. Every value carries its source and its basis in the public dataset.