The "5000" is the nameplate capacity of the turbine in watts, whose cut in wind speed is 2.7 m/s and whose most effective operating range is stated to be 4.5 to 9 m/s (for the SI unit impaired reader, these are 6, 10, and 20 m.p.h. respectively). It's a vertical axis wind turbine (VAWT) and thus is agnostic with respect to wind direction. The turbine itself is fully enclosed, thus eliminating the possibility of bird and bat kills.

In an interview at the CleanTechies blog, Sheikhrezai claims that the Turbo Windmill 5000 utilizes a proprietary vacuum system that "captures and funnels turbulent wind in a smooth, counterclockwise stream" and that thereby "a vortex is created beneath the internal turbine enabling a vacuum effect, pulling more wind into the frame and amplifying input loads." Sadly, he then states that "energy available in the wind is proportional to the cube of its speed." This is false, power is proportional to the cube of speed, energy is proportional to the square of speed. We'll forgive Sheikhrezai this transgression. Sheikhrezai states that the Turbo Windmill 5000 can produce 10,000 kWh per year with an average wind speed of 7.2 m/s (a bit over 16 m.p.h.).

OK, let's dive into a "back of the envelope" plausibility calculation. Using the photo above and assuming that the 9' dimensions are horizontal, the 10' dimension is height and that the only wind entrance is the "yellow" portion, I can use Tracker to scale the wind accessible dimension as 7.25' X 3.43' or 2.31 m^2. First, what's the total power in wind of cross sectional area of 2.31 m^2 travelling at 7.2 m/s? We have a volume, ~V~, of 7.2 meters X 2.31 meters passing any given point in one second. The air's density, ~\rho~, (assuming sea level - most favorable for the calculation) is 1.225 kg/m^3. We use ~E=1/2\,m{v}^{2}~ and ~m=\rho\,V~ for ~E=1/2\,\rho\,V{v}^{2}~ or

*Update: Thanks to Ed Davies for causing me to take a look and realize that I'd been off by a couple of orders of magnitude (using 122.5 instead of 1.225 kg/m^3 for sea level mass density of the atmosphere). How embarrassing!*

*So, what to make of the claim of 5 kilowatts? Working backwards, what would this imply for a wind speed? Betz' law provides the theoretical limit of turbine efficiency (the maximum fraction of the energy available in wind that can be captured) at about 59%. The best efficiency I've seen for a turbine is about 70% of the Betz limit or, in round numbers, 42% of the power in the intercepted wind. This is achieved by horizontal axis turbines (typically much more efficient than VAWTs) of enormous size at ideal wind speeds. But let's generously assume that the proprietary vacuum effect enables Windation to capture and utilize 45% of the wind's power. So, 0.45*(available wind power)=5000 watts and available wind power is 5000/.45 = 11,100 watts. Working backwards and solving the equation above for speed and plugging in 11,100 watts, we find a wind speed of 19.9 m/s or just under 45 m.p.h. And the generous assumptions are beyond unlikely to be met in a real installation.*

With respect to the claim of 10,000 kWh/year at average wind speed of 7.2 m/s, it's hard to say. "Average" doesn't work well here. Say we had an hour of wind at 7 m/s and an hour at 7.4 m/s. Then say we had 4.2 m/s and 10.2 m/s. Because of the proportionality of power to speed cubed, the two hour span with the more extreme speeds would generate about half again as much energy yet both have, in a sense, the same "average" wind speed. That said, if the Turbo Windmill 5000 generates 5000 watts for a year (365.25*24 or 8,766 hours) it would result in 43,830 kWh so it doesn't seem like an excessive claim (

*IF, of course, it can generate 5kW)*. No cutoff speed is given. Much deeper information on wind speed distribution is here.

*Update (see above): 10,000 kWh/year is a continuous power of (10,000 kWh/year)/(8,766 hours/year) or 1,140 watts. Proceeding as above, with the generous assumptions there, we're talking about a steady wind of 9.3 m/s or 21 m.p.h. Now, admittedly, a variable wind that has periods of very high speeds may improve on this but, on the other hand, my efficiency assumptions are extremely generous and highly unlikely to be realistic.*

Finally, I have to point out that 10,000 kWh would cost me about $1,200 from the City of Anaheim Public Utilities. The price for a Turbo Windmill 5000 given at the web site (where, sadly, I found the sentence "the machine can generate 5 kilowatts of power per year") is $45,000. It's implied but not stated that this includes installation. The claim is that "With the available incentives and rebates, it is estimated that the initial expenditure of $45,000 can be recovered in five to seven years." Payback period is a poor indicator of the desirability of an investment when considering periods beyond two years, but even with that, we must be talking about a LOT of rebates and incentives.

So:

Energy claim: Economics claim:

*Update: An excellent overview of building integrated wind is here.*

*Update 2: While looking for further information to attempt to better understand Windation's claims, I noted that the article linked above was published in 2010. I'm not sure why it wound up in my inbox recently, but I decided to see if the firm is still a "going concern." The last update on their web site is from November of 2012 and I find no record of bankruptcy proceedings. However, their corporate address is 1007 Florence Ln., Apt 1, Menlo Park CA. Here's a Google Streetview screen shot of their corporate HQ:*

*Windation has claimed that they'd install a unit at the Palo Alto Medical Foundation in the first quarter of 2010. I located architect's renderings of the installation and then found the facility as constructed in (where else?) Google Streetview, and the Turbo Windmill 5000 was not installed as of the photo date of March, 2011.*

*Doing a lot more reading about "building integrated" and "urban" wind, the field seems to be full of dodgy claims and outright scams. I don't know which category, if either, Windation falls into but a lot more information on these topics can be found at Paul Gipe's site. The pertinent information is here.*

*Update 3: In my further digging, I located a video of an actual unit (well, possibly an actual unit, one can't really tell as it's sitting on some sort of pavement area and the intake is covered). But something does, in fact, exist. The video was uploaded on November 5, 2011 and Windation left a response to a viewer comment "a year ago." The video is FAR from professionally produced. It's embedded below for your viewing pleasure.*

*I have to say that this is very disturbing in that false claims, vaporware and dubious business practices provide ammunition for those who would claim that renewable energy is a chimera and that increased business as usual is our only option. It further muddies the water with respect to what constitutes sound investment opportunities in the so-called "green space." Finally (yes, finally), it's a shame that the "green press" uncritically embraces such products and schemes without doing the necessary evaluation.*

## 7 comments:

52,800 joules each second or a power of 52.8 kilowattsAre you sure; that's 100 times what I make it and, from the little knowledge I have of actual turbines, totally implausible.

Here, by the way, is my version of the calculation that I did before reading yours:

9'x10' is roughly 3 metres on each side so 9 m². Power available in the air at the upper end of their optimal speed range is ½Aρv³ = 0.5 * 9 * 1.2 * 9**3 = 3936.6 W (using a slightly lower value for air density from memory) but turbines are restricted to extracting roughly 59% of the available power by Betz law so a maximum of 2332 W. Practical turbines will extract less.

Hence my double check of your calculation.

Thanks for busting me here! Somehow, I used 122.5 kg/m^3 instead of 1.225. But what's two orders of magnitude between friends?

I've made appropriate revisions to the post.

While I agree that the Turbo 5000's payback period would be *much* longer than the 5-7 years claimed and is unlikely to be a good investment, I must disagree with your statement "Payback period is a poor indicator of the desirability of an investment when considering periods beyond two years".

Assuming high durability, a 5 year payback is like earning 20% tax free! Of course durability isn't perfect, and there would be maintenance costs, but if a device with a 5 year payback had a useful lifetime of 25 years, and annual maintenance of 2%, then it's still about a 14% tax free return. That sort of calculation is *highly* dependent on payback period though. Double the period from 5 to 10 without changing the other assumptions, and the return drops from 14% to 4% per year.

So, I wouldn't buy the Turbo 5000, when I'm confident that payback on a home solar PV would truly be less than 10 years, I'll get serious about installing it.

Bleh, typo last line.

"So

althoughI wouldn't ..."Hi Greg, when considering capital investments at my firm, we typically assume a cost of capital of 8%. In deciding where to invest, we decide to invest here and not there by comparing the NPV of the cash flows using the 8% discount rate. "Payback period" doesn't take time value of money into account. Over a short period, this doesn't distort too much but over longer periods it can be misleading. NPV and IRR calculations are "pure" in this sense (though determining what to use for a discount rate can be very problematic and is crucial to the value of the calculation).

Of course, the payback period method can be modified to capture this but, even then, it doesn't capture cash flows post-payback.

Capex decisions are rarely, if ever, made in a vacuum. It's typically "shall I invest in this, that, or the other" and payback is not a good analysis method for longer term cash flow considerations.

Your mileage may vary, of course.

I wasted a month of my life consulting for Windation in 2007. Small urban VAWT energy has very little chance of ever becoming viable for the reasons you have mentioned. Paul Gipe's site is a great service to humanity, and so is yours.

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