I'm at the ASNT (American Society for Nondestructive Testing) Fall Conference and Quality Testing Show in downtown Houston, TX. I'm staying at the Hilton Houston Americas, with a northward view across Disovery Green Park. I was here in May of 2009 for the Clean Technology Conference and Expo and saw an office building under construction. It's now completed, it had been called Discovery Tower but has now been renamed Hess Tower since the Hess Corporation (formerly Amerada Hess) leased all 872,000 square feet of space in the building.
As I looked out my 11th floor window at the 30 story tower, a spinning motion caught my eye. I looked up at the tower and, sure enough, there appeared to be a series of vertical axis wind turbines adorning the top of the tower. They are certainly eye-catching and, to my uneducated eye, add to the visual appeal of the building. But do they provide enough energy to justify their cost to manufacture, install, and maintain?
Information as to the cost and expected energy output is sparse in the google-verse though I did see that Cynthia Cisneros of KTRK did a brief television piece about it. She exhibited her and her editor's cluelessness by stating that each of the 10 turbines is "designed to generate approximately 3.5 kilowatts per hour." She does state (and I've read at a couple of other sites) that the turbines should generate sufficient energy to light the building at night or to power two office floors.
I was able to finally determine that the turbines are manufactured by Cleanfield Energy, headquartered in Ontario, Canada and that they are Cleanfield's Model V3.5. They're "designed to harness urban wind efficiently and effectively." On their web site Cleanfield provides a specification sheet for the turbine which I would copy here if it weren't for fear of a lawsuit.
But using the "Estimated Energy per Year" chart and an average wind velocity of 4.5 meters/second (downgraded for the urban setting from an 80 meter wind average wind velocity chart here) I'll estimate that each turbine will provide about 1,500 kilowatt hours/year for a total of 15,000 kilowatt hours/year, or 15 megawatt hours/year. Note that this is a capacity factor (assuming 3.5 kilowatts rated power) of 1,500/(3.5*24*365) * 100% or about 4.9%.
Now, I suppose that Hess Corporation gets a better deal on energy than I do, but it's probably not too far off to figure they pay about $0.10/kilowatt hour. So, by avoiding the purchase of 15,000 kilowatt hours they'll save something like $1,500. I don't know what the generators cost but I suspect that the net present value of the investment is negative no matter how small Hess' cost of capital.
I've found a couple of estimates for electricity use in office buildings on a "per square foot" basis, at 18.9 and 17 kWh/year. If I assume that the Hess building is MUCH more efficient at, say, 15 kWh/year/ft^2, then at 872,000ft^2/30 floors there are about 29,000 ft^2/floor. Two such floors would use 870,000 kilowatt hours/year. Use of a median rather than an average electrical energy usage might cut this number by about a third (very optimistically) so let's say 580,000 kilowatt hours/year might be a reasonable lower bound. I don't think the turbines will do it. They'd supply about 1,250 ft^2, a small office.
A video is here:
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