An order came in from Niigata Prefecture this month: one Atlas and a set of blades. Every order has an address, but this one is going to the place the Japanese call yukiguni, snow country — the coast where Siberian air crosses the Sea of Japan in winter, picks up the sea, and drops it as some of the deepest snow that falls anywhere people live. It is a hard place for a machine and a very good place for a wind turbine, and the two facts are the same fact.
Where the wind comes from.
Niigata faces north-west, across the Sea of Japan towards the continent. In winter the pressure pattern over Asia sends cold, dry air out of Siberia and across that water. The sea is warmer than the air, so the air fills with moisture; then it meets the mountains that run down the spine of Honshu, is forced upward, and lets go. The Niigata side of those mountains gets the snow. The Tokyo side, a short train ride away, gets the sunshine.
The same pattern is why the wind here is a winter wind. The north-westerly comes in off the sea steadily and hard from December to February, exactly when the days are shortest and a solar panel under half a metre of snow is producing nothing at all. A house in Niigata that wants to make its own electricity through the winter needs something that works in the dark and in the cold. That is the whole case for putting a turbine next to the panels rather than instead of them.
What cold air is worth.
A wind turbine does not make power from wind speed alone. It makes it from the mass of air passing through the rotor, and cold air is heavier. Our published power curve is quoted at the standard air density of 1.225 kg/m³, which is sea level at 15 °C. Niigata’s coast in January sits close to sea level and close to freezing. At 0 °C the same wind carries about 5% more mass than the curve assumes; at −5 °C, about 7% more. A winter gust that would read 960 W on the curve at 12 m/s is worth a little over 1 kW in Niigata air.
That is a small bonus, and we would rather state it precisely than let it grow in the retelling. The larger point is that the wind is there at all, in the months when it is needed, on a coast where the sea keeps the air moving.
| Wind speed | Published, 15 °C | Same wind at 0 °C | Same wind at −5 °C |
|---|---|---|---|
| 8 m/s | 290 W | about 305 W | about 310 W |
| 12 m/s | 960 W | about 1,010 W | about 1,030 W |
| 15 m/s | 1.85 kW | about 1.95 kW | about 1.99 kW |
| 18 m/s | 2.15 kW | about 2.27 kW | about 2.31 kW |
What snow does to a machine.
Snow country earns its name. Towns in the Niigata hills routinely measure their winter snow in metres, not centimetres, and the houses are built for it: steep roofs, raised entrances, heated pavements in the town centres. A turbine going there has to be built for it too.
The Atlas is a vertical-axis machine. It does not have to turn to face a wind that swings round the compass in a storm, and it has no tail to be loaded up with ice. Its windings carry Class 200 °C insulation (IEC 60317-13 GR 2), which is a thermal margin the machine will never use in Niigata but which says something about how it is made. The body is aluminium, which does not care about salt from the sea or meltwater from the roof.
The honest caveat is start-up. We publish a 2 m/s start-up speed and it is a fair-weather number. Bearing grease stiffens as it cools, and a still, freezing morning wants more than 2 m/s to break the rotor away from standstill. In Niigata that hardly matters, because a still morning on that coast in January is the exception, but we would rather say it than have an owner discover it.
The mountain takes the snow. The sea sends the wind. A house in between can use both.
The blade set decides the winter.
An Atlas is ordered as a body and a blade set, and the set is the decision that matters. Low-wind blades run from 2 to 20 m/s and must come off before sustained winds above 20 m/s. Moderate-wind blades run 4 to 25 m/s. High-wind blades run 5 to 35 m/s on six blades with a smaller swept area, and that is the set the 4.5 kW peak belongs to.
On a coast that sees winter gales off the sea, the choice is between the blades that flatter the average and the blades that survive the storm. We say the same thing to every customer: choose the set for the worst wind your site sees, not the mean, and let the quiet days take care of themselves.
Rice, snow and a pallet from Europe.
Niigata grows more rice than any other prefecture in Japan, and the terraces in the photograph at the top of this page are the reason it can: the same snow that buries the villages in January melts into the paddies in April. It is a landscape that has always run on what the weather delivers for free. A small turbine on a house there is not a novelty. It is the same idea, with copper in it.
The Atlas and its blades are being packed at our factory in Europe now, each carton labelled individually, and will cross a good deal of sea of their own on the way. When they arrive, the winter wind will already be waiting.
Snow country.
Winter wind.
Atlas, on its way.
The power-curve figures, the 2 m/s start-up speed, the three blade ranges, the 4.5 kW peak system output, the Class 200 °C wire grade (IEC 60317-13 GR 2) and the per-unit labelling are our own published product-page specifications and can be read there. The cold-air figures are the ideal gas law applied at constant pressure: air at 0 °C is about 5.5% denser than at 15 °C, and at −5 °C about 7.5% denser. The description of Niigata’s winter climate, snowfall and rice production is general geographic knowledge. The order is described only by prefecture and product; no customer, address or installation is named or shown. Photographs: Hoshitoge rice terraces, Tokamachi, by Fumihiko Ueno via Wikimedia Commons, CC BY 3.0, cropped; Sasagawa Nagare coast, Yuzawa ski slope and Minamiuonuma morning licensed via Adobe Stock; the Atlas photograph is our own.