Typhoon Dujuan is moving up Japan’s Pacific coast with sustained winds of 130 km/h and gusts of 194 km/h. Almost two million people have been told to leave their homes. Two people have died. More than fifty thousand have already lost power. It is the country’s twenty-fifth typhoon of the year, it arrived in the middle of a five-day holiday, and it is still heading north.
We sell wind turbines, and this is a post about wind, so let us be clear about the argument before we make it. A storm like Dujuan is not an opportunity for a small wind turbine. It is the one day of the year when the correct amount of electricity for it to make is none at all. What follows is what those numbers mean for a machine on a pole, and what we tell owners in its path to do before it reaches them.
Thirty-six metres per second.
Engineers talk about wind in metres per second, so translate: 130 km/h sustained is 36 m/s, and a 194 km/h gust is 54 m/s. For scale, a good site for a home turbine averages 5 to 7 m/s. The Atlas reaches its rated output at 15 m/s. Dujuan’s steady wind is more than double that, and its gusts are more than three times it.
Wind power rises with the cube of wind speed. Double the speed and the energy in the air goes up eight times; treble it and it goes up twenty-seven times. That is why a turbine that is comfortable at 15 m/s is in a completely different world at 36, and why the loads on blades, bearings and mast in a typhoon are not “a bit more” than on a windy day. They are an order of magnitude more.
Every blade set has a ceiling. This is above all of them.
The Atlas ships with a choice of three blade sets, and each is rated for a band of wind. The Low-Wind set, which most homes choose because it starts turning at 2 m/s, is capped at 20 m/s. The Moderate set runs to 25. The High-Wind set, six shorter blades with a smaller swept area, is built for storm-prone coasts and is rated to 35 m/s. The Magnum reaches its peak at 22 m/s and is protected above that by its charge controller.
Dujuan’s sustained wind is 36 m/s. Read that against the list above. Nothing we sell is rated for it, and we would not want you to believe otherwise. The High-Wind set is the right choice for a coast that sees 30 m/s a few times a winter. It is not a licence to leave a turbine running through a named typhoon, and no honest manufacturer of small turbines will tell you theirs is.
A blade set’s rating is the wind it is designed to work in. A typhoon is the wind it is designed to be taken down before.
Stop it before it arrives.
The good news about a typhoon is that it is forecast. Dujuan has been tracked across the Pacific for days, and the satellite timelapse shows the eye and exactly where it is heading. That gives an owner what a sudden squall does not: time. If it is heading your way, this is the afternoon to use it.
First, brake it. The charge controller — built into the Atlas, a separate unit for the Magnum — lets you set a voltage limit, and once output passes that limit it holds the turbine back electrically. Set the limit low and the turbine is effectively parked. That is what the brake is for: gusts on the edge of the rated band. It is not a substitute for the next step when the forecast says 36 m/s.
Then cover it. The Atlas Protection Cover exists for exactly this day. It goes over the rotor and holds the blades so they cannot turn, and it is bright yellow so that it is quick to fit and easy to see from the ground that it is on. Our own instructions say the Low-Wind set must not be left running in sustained winds above 20 m/s, and the same logic applies to every set once the forecast passes its rating: a rotor that cannot turn is not building up speed, and a turbine that is not building up speed is not shedding load into its bearings and mast. If you have no cover to hand, removing the blades does the same job the hard way.
Then check it is quiet. If your turbine is connected to MyTESUP, the app will show you whether it is online and what it is producing. In a typhoon the number you want to see is zero, and you want to see it from indoors.
The grid comes back last.
More than fifty thousand people have already lost power to Dujuan, and power cuts are the part of a storm that outlasts the storm. The wind drops in hours; the lines are repaired in days. This is where a small turbine earns its place, and it is worth being precise about when. Not during the typhoon, when it should be stopped. Afterwards, when the wind is back to the 8 to 15 m/s that a passing storm leaves behind for a day or two, and the grid has not yet returned.
That is a turbine-and-battery question, not a turbine question. A turbine alone gives you power when the wind blows. A turbine charging a battery gives you a fridge, a phone and a light on the evening after, whatever the wind is doing at that moment. If you live on a coast that sees a typhoon season, size the battery for the outage, not for the sunny week.
For owners on an exposed coast.
Know the ceiling of the blade set you have on the pole, in metres per second, and know how the local forecast reports wind so you can compare the two without arithmetic on the day. Keep the cover where you can find it, and practise fitting it once on a calm afternoon, so the first time is not in a rising wind. Keep the brake limit somewhere you can change it from your phone. And if the forecast says the storm has a name, the plan is the same for every turbine we make: brake it, cover it, and go inside.
If you are choosing a turbine for that kind of coast, the blade-set ratings for the Atlas and the storm protection on the Magnum are on their product pages, in metres per second, and the cover is a small line on the order that you will be glad of once a year. Read them the way you would read a forecast. Our thoughts are with the people on Japan’s Pacific coast who are in its path this week.