Assistant Town Planner Gary Crosby at the WTG terminal

One of the tidbits in last Monday's Portsmouth Town Council meeting was the report that, in its first month of operation, the Wind Turbine Generator (WTG) had made the town approximately $35,000. Earlier this week, I stopped by Town Hall to find out where those numbers come from.

Gary Crosby is Portsmouth's Assistant Town Planner, and he, along with Portsmouth EDC member and Sustainable Energy chair Gary Gump, gave an overview of the monitoring system provided to the town by turbine manufacturer AAER. There are two SCADA terminals in town, one at Town Hall and one at the Fire Department.

"The one at Town Hall is just there to monitor, there is one in the fire station with operational controls," said Gump. "They have a big red button that can start or stop the turbine."

Physically, the "SCADA terminal" is just a web application on a computer sitting next to the rack of gear that occupies a corner of business development director Bill Clark's office. There are several screens of graphical information, showing real-time as well as historical data about all aspects of the WTG's operation.

WTG terminal at Town Hall

"There are a gazillion sensors," said Crosby. "The datastream goes to [AAER's] Canadian center where they monitor the operational parameters in their surveillance facility. Then the datastream is sent back here."

On that day, the terminal showed that the WTG was producing about 400 kilowatts. The turbine has been set to artificially lower production limits during its run-in period, Crosby explained, as AAER captured wind data to tune the turbine for the local conditions. All of this is covered under the warranty and the maintenance contract with the manufacturer.

But even in these early results, "the averages are what we would expect," Gump said. The turbine produced power for 427 hours since March 18, generating 252 megawatts.

There are two income streams which add up to the $35K number, Gump explained. "One is per Renewable Energy Certificates (REC), which are 4 cents per kilowatt. So 250 [megawatts of] RECs is about $10,000. And the electricity generated, for which the approximate revenue is about 10-11 cents per kilowatt-hour, so between $25-27,000."

The numbers are approximate, because the Town actually gets the generation revenue as an offset against usage. "We'll have to wait till we see our first power bill," said Crosby. "According to regulations from the Public Utilities Commission, we don't get to credit all our accounts, just the top 5 [town meters]."

For the present, the numbers are being posted on the bulletin board across from the Town Clerk's office, but Gump said they are working with AAER to see if they can figure out a way to post the data on the Town web site.

And Crosby and Gump took the opportunity to explain the difference between the Town turbine and the one at the Abbey. They had gotten some questions about why the Town turbine turns more slowly, and why it doesn't appear to spin as often as the one at the Abbey.

"The turbine at the Abbey is always turning; that's a design decision," said Crosby. "But it's not making power until it reaches 28 rpm. Ours will not turn when the wind speed is below 3.3 meters per second [7 mph] but as soon as it starts turning, it is producing power. And it when the wind reaches 11.5 meters per second [25 mph] it is turning as fast as it ever will. Never faster than about 19 rpm. Compared to to the Abbey — at 19 rpm they haven't even started producing yet, but we can generate 2.5 times the power."

Gary Gump explains control panel in WTG.

Gump had to take some photos inside the turbine, so I tagged along. The first thing you notice, approaching it, is the difference in sound. When you're up close to the Abbey turbine, there is a definite, individual sound as the blade descends, not quite a "whump," but a distinct sound. At the Portsmouth turbine, even standing directly below it, there is only a vague, sustained "whooshing" as the blades rotate. My sense is that it is significantly quieter. Part of it is likely due to the height of the tower, but the aerodynamics of the blades helps.

"The blade technology improves every year," Gump explained.

The loudest sound at the base is actually the hum from the step-up transformer that brings the WTG output of 690 volts up to the 13.5kV for the grid.

There is a bulkhead door at the top of a short flight of metal steps. "The Fire Department has a key," Gump said. Inside the base, there is a central panel showing readouts on the power coming down from the generator, and a control panel on the wall that mirrors the information on the SCADA display. In the middle is s big red button. "That's the emergency stop," said Gump.

There is a thrumming echo inside the tower; not loud, but constant, and you can feel vibration in the walls. "You have to imagine the dynamic stress," said Gump. "The torque from the blade at the top is going to be different than the blade at the bottom."

Outside the turbine, the construction equipment has been removed, but the site is still being restored. Eventually, all the hay bales will be gone and it will look pretty much as it did before. At the base of the approach road, a new National Grid meter tracks the power being generated.

"We haven't looked at that meter," Gump said, "But we're comfortable that the production will be close to the model in the economic feasibility study."

Resources:
Pictures from tour up on Flickr
Visit the Portsmouth Sustainable Energy site for more info.
Visit AAER to learn more about the folks who made the turbine. (Great team picture here.)

Editorial note: Thanks to former water board member Rich Gottlieb for explaining SCADA terminals and setting up the show-and-tell.