Beating a Dead Horse–More on Smith-Putnam’s 1,000 kW Rating

By Paul Gipe

Since I posted my article on the revised rating of Smith-Putnam’s famed wind turbine of the 1940s, I’ve received several comments. (See When is a 1,250 kW Wind Turbine Only 1,000 kW? Setting the Smith-Putnam Record Straight.) One was from an old wind hand, Mark Haller. Others also noted the historical record is rife with the error.


“I found a couple interesting references in EW Golding citing 1250 kW. There is one reference saying 1500 kW in a table,” Haller wrote.

And back down the rabbit hole I went.

Haller’s copy of Golding’s seminal work, The Generation of Electricity by Wind Power, had been gathering must and mildew in his collection before this discussion brought it back into the light.

Indeed Golding, who one might say is the father of British wind energy, makes numerous references to Putnam and his project. Beginning on page 3, Golding identifies the Smith-Putnam turbine as a 1250 kW based on Putnam’s book and continues referring to it as 1250 kW throughout.[1]

The only exception, as Haller noted, was in a table of different wind turbine designs on pages 220 and 221, where Golding makes reference to a proposed 1500 kW wind turbine with a rotor diameter of 200 feet (61 meters) based on a report by the (US) War Production Board in 1946.

Haller suggests that it could have indeed been rated at 1250 kW. “The strip chart in Putnam’s book shows excursions up to at least 1200 kW, considering that the resolution in a strip chart isn’t very good. In high winds, every synchronous full pitch turbine we know of would jack power spikes more significantly than that shown in the strip charts. Perhaps Putnan learned this the hard way and down-rated the machine to 1000 kW,” writes Haller. “Yes, that’s a guess,” he says.  “But, consider the speed and accuracy of pitch control measurement and analog response time lag, and it is likely that this machine was misbehaving in winds above rated power.”  

In the end, Haller—like most of us—says, “I want to see the nameplate on the generator” before concluding what it was really capable of.

Johannes Juul

Rémi Gandoin pointed out that Johannes Juul got it wrong too. In a 1954 report on his Gedser turbine, Juul wrote that the largest wind turbine built to date was that designed by Putnam. Juul proceeded to describe the turbine and noted that “at 16 m/sec wind it developed 1500 kW and at 12 m/sec about 700 kW.”[2] Juul doesn’t say where he got that number and he doesn’t refer to it as the “rating” only that the turbine did deliver that power. Juul could have simply mistaken what Putnam had written. Or Juul could have corresponded with Putnam or studied some of the Smith-Putnam records. We don’t know.

It’s noteworthy that Juul specifies 1500 kW at 16 m/s. That’s a significantly higher wind speed (38 mph) than the Smith-Putnam’s rated speed of 30 mph (13.4 m/s). So it’s conceivable that the turbine did reach that power output at some point.

Nevertheless, it’s clear from the strip charts that Putnam published in his book that the turbine was regulated to deliver ~1000 kW regardless of whatever power excursions may have occurred.

Tvind’s 54 m Turbine Larger than Smith-Putnam

As I noted in my original post, it doesn’t really matter what the “rated power” of the turbine was in the end, it was a giant wind turbine for its day with a rotor 175 feet (53.4 m) in diameter.

Göran Ronsten reported an interesting anecdote. Ronsten says that in 2002 Per Lundsager told him that the Tvindkraft turbine at the Tvind school on the west coast of Denmark’s Jutland peninsula was designed to be just slightly larger than the Smith-Putnam turbine. Thus, Tvindkraft is 54 m in diameter. For now, this story remains in the category of hearsay and is possibly apocryphal. I haven’t been able to confirm it.

What we do know is that the Tvind school enlisted the technical support of wind experts from Denmark’s Risø laboratories. This assistance was “off the books,” but was crucial in making the project such a success. These experts would have been familiar with the Smith-Putnam project and its pertinent parameters, such as rotor diameter. So if Tvind wanted to build the biggest windmill in the world they likely knew it had to be 54 meters in diameter or greater.

For those who don’t know the fascinating story of Tvindkraft, it began operation in 1978 and was built by the school’s students. And it is still operating today, one of the oldest if not the oldest wind turbine in the world. (See Birthday Celebration for the World’s Oldest Operating Wind Turbine, and Tvindkraft: The Giant That Shook the World Turns 42.)

As Klaus Kaiser has pointed out it was originally rated at 2 MW and by that standard was one of the most powerful wind turbine of its day, rivaling that of General Electric’s Mod-1. However, as Kaiser notes, it was down rated to 900 kW because of limitations to the power conversion system and the distribution system it was connected to. GE’s Mod-1 was also 61 meters in diameter, so considerably larger than Tvindkraft in rotor diameter.

While Tvindkraft was technically smaller than GE’s Mod-1, it was slightly larger than the Smith-Putnam machine. Most importantly, Tvindkraft outperformed both. Like the Smith-Putnam turbine, Tvindkraft eventually lost a blade. However that didn’t spell the end of the turbine. It was returned to operation with a new rotor that remains in service to this day.

[1] Golding, E.W. The Generation of Electricity by Wind Power. Reprinted by John Wiley & Sons 1976. London: E. & F.N. Spon, 1955, pp. 3, 19, 78 (photo), 125, 185, 220 (table).
[2] J. Juul. “Results Obtained with the Experimental Windmill of Sydøstsjællands Elektricitats Aktieselskab-Seas Co. Ltd. Haslev, Denmark.” In Technical Papers Presented to the Wind Power Working Party: Committee for Productivity and Applied Research, 313–70. Technical Paper No. 38. Paris: Her Majesty’s Stationery Office London, 1954, p. 340.