Whisper H40 Final Report

By Paul Gipe


We returned to the site to remove the turbine for repair. The blades were removed without incident. However when removing the generator-yaw assembly the entire assembly came off in my hands without the yaw bracket. The yaw bracket remained firmly wedged in the tower top. This forced me to cut the conductors to get the assembly out of the way. Normally the conductors are secured to the down tower conductors with set screws.

Not only the rotor was unusable with the broken blade and the insulation blown on the generator windings but the yaw assembly had failed as well.

I called Southwest Windpower for a repair authorization. This model is no longer supported, so SWP suggested a replacement at wholesale cost for $1,350.

While lightning is still the most likely cause of the turbine’s failure, there is another possible cause. It’s conceivable that the yaw assembly failed first, allowing the turbine to run fully into the wind during a period of high winds leading to cascading failures.

This concludes the tests on this turbine. This unit will be scrapped.

This model lasted four years under our conditions.

May 17, 2006


We inspected the turbine from the ground with binoculars and one blade was indeed damaged. We then took the turbine down using the griphoist technique that we have documented previously. The rotor had been struck, probably by lightning sometime in late 2005.

The surface of all blades were crazed from the intense sunlight at the site. (It was 35-38C when we took the turbine down!)

There was a gray dust or powder coating the underside of the generator. It wasn’t clear what this was from but it was new since the last time we had seen the turbine up close.

Upon close inspection, there were visible openings in the insulation of the wiring from the windings to the diode block. There were more than one place where the insulation was open and ragged. Two such openings are visible in the following photo. The generator is clearly damaged and will need to be replaced. The damage was likely caused by lightning. As thunderstorms were threatening, we didn’t remove the turbine. We will return later this summer to remove the turbine.

December 22, 2005


In mid December we made an inspection visit to the Wulf Field. We found the Whisper H40 with 1/3 of the outer edge of one blade missing. There was no wind and neither turbine at the site was turning. We had inspected the site one month prior to our December 2005 visit. There were signs that someone had trespassed on the site but no tools were missing and there were no signs of vandalism. Someone could have shot the blade but we have no way of telling until the turbine is removed from the tower. We braked the H40 with the provided brake switch and left the site.

December 8, 2003

by Paul Gipe

Key words: H40, Whisper, Southwest Windpower, Small wind turbine testing.

I removed a Bergey 850 in the late fall of 2002 and during the winter of 2001-2002 installed a Whisper H40 manufactured by Southwest Windpower.


At 7 feet in diameter (2.1 meters), the H40 is slightly smaller than the Bergey 850 it replaced, and sweeps about 40 square feet (3.6 square meters), hence the designation: H40.

While still a product of World Power Technologies the H40 was rated at 460 watts at 10 meters/second (22 mph). During the transition to Southwest Windpower the rating was dropped in favor of the swept area designation and a reference to a peak power of 900 Watts at 28 mph (12.5 m/s).


The packaging was adequate. The blades were well protected but the generator was crudely packed in foam and flakes of foam were wedged in the generator body. All parts needed were included.

Disclosure: Two AirX turbines as well as a Whisper H40 were provided by Southwest Windpower to Paul Gipe at no charge in lieu of noise measurement services provided by Paul Gipe.


Again adequate. The installation manual offered good visuals explaining the turbine’s assembly.


The H40 is a very simple turbine and assembly was very straightforward.


I mounted the H40 on an NRG 65-foot hinged mast of 4.5-inch tube. This is a non-standard application for the H40 and I had to have an adapter made at a local machine shop.

Control Panel

The control panel was less sophisticated than the old World Power panel. There was no meter. But there was a brake switch and it worked under light to moderate winds. The panel was ruggedly constructed and easy to mount. The arrangement for the terminals for the conductors were much better than for the BWC 850.


The turbine is relatively quiet and operated without problems for nearly two years (from early 2002 to December 2003). I removed the H40 to free up the tower for tests on a Bergey XL1.

Power Curve

Like several of the turbines I’ve tested, the H40 does not meet the manufacturers power curve. Corrected for sea level conditions the turbine peaked at about 700 watts at 28 mph or 200 watts less than the manufacturer claimed. Even so, my 1-minute measurements were considerably higher than the 10-minute averages recorded by NREL’s Power Performance Test Report for the Whisper H40.

I ran the tests again in the spring of 2003 and found no deterioration in the power curve.


I detected no external deterioration of the turbine when I removed it from the tower after nearly two years of operation in the Tehachapi Pass. Though this turbine does not meet its advertised power curve, the H40 has proven reliable and trouble free. It’s “a keeper” and I have no qualms recommending the H40 to others. (This recommendation applies only to the H40 and not to the H80.)

Power Curve

Scatter Plot

Power Lost in Conductors

My tower was on the edge of the recommended cable length for #8 AWG copper. The power lost in the conductors would have been slightly reduced by using #6 AWG copper.

Annual Energy Generation

Note that even though the H40 does not meet the manufacturer’s advertised power curve, it will deliver as much energy as the manufacturer claims.

Test Confirmation

Tests by Applachian State University have confirmed the power curve measured at the Wulf Test Field. See Whisper H40 ASU Power Curve.