Wednesday, July 8, 2009
Testing a new anemometer system
Anemometer systems are expensive. Our Community Wind Assessment program has two of the professional level kinds made by NRG Systems, one for buildings with a tower, one for open country sites with a guyed tower. These systems cost around $4,000 and $17,000 respectively.
However, I have just received a new, much cheaper device to check out, made by RainWise of Bar Harbor, called the Wind Log. I was contacted by two different community wind sites where these devices are in use, and so I called the firm to find out if they were seriously marketing the devices for large scale turbines. It is generally not advisable to use personal weather station equipment, which these devices really are, to measure the wind for industrial scale turbines.
However, despite my skepticism and desire to encourage proper practices, when I called them the company offered to give me one to test out, so I thought I'd do a good scientific job of it and try to make it work properly for industrial scale wind power sites.
I fabricated a small test tower of PVC pipe to test the device on my front lawn before putting it out on the site we have at the Charleston Correctional Center. Once it's been on the lawn for a couple days and I have checked out the sensor and logger, I plan to run it side by side with my smaller NRG rig, already in place on that site, for a couple of months to check that it collects valid data. The results from both rigs should be statistically the same.
The main problem with this device is that it doesn't come with a tower. A minimum of 100 feet of tower is generally advised for anemometry for serious wind turbines. I recommend 50 and 60 meter towers for wind farms using the larger GE and Vestas turbines. Already the folks that are using these for serious turbines are both also using too short a tower.
The other problem is that it only has one wind speed sensor, whereas two are required to get the wind shear factor, one of the basic anemometry statistics. Two are also recommended in case one quits. Our NRG 60 meter sensors come with three banks of two wind speed sensors, typically at 40, 50 and 60 meters, as well as two directional vanes.
However, these devices are cheap, around $350. There are several wind power projects in Maine that are stalled right now because the two anemometer loan programs in-state, ours and the one at UMO, only have a handful of anemometer systems available for loan, four last time I counted. That's because the systems are so expensive.
With some tinkering and rewiring, you could afford to buy two or more and place them on the same tower at different heights.
And lots of different tower systems are available.
The rewiring would be needed to get the heavier logger box away from the sensor so the sensor could be placed on a standard boom arm. This is needed to place a sensor on the side of a tower instead of the top, which is what the device is currently built for. I didn't see any particular difficulty doing this. It's just wiring. Possibly once the company figures out what is needed they will offer the new wiring set up as an option or extra.
My friends at NRG will be pretty mad with me if I figure out a way to seriously measure the wind with these devices, however modified. They've been stalwart supporters of our work for several years.
But that's science and engineering, folks. The cookie doesn't always crumble your way. Like Popeye, who "yam what I yam," data and results "is what it is."
As always, you can expect us to provide objective reporting.