Tuesday, January 6, 2015

Detailed photos of the Bibles Farm turbine project

Brent and Erin took a sequence of pictures during the raising of their new Maine-made Pika wind turbine, so students could see how the process works. The first photo shows the overall setting with the tower raised. This is an off-grid farmhouse. Over to the left you can see a small shed with the solar array on the roof. This was the existing system. I'm not sure how large, but I'd say it's less than a kW, so the most power it could provide on a midwinter's day in Maine would be roughly 2.5 kWh. That's enough to watch TV or run a computer for a few hours, to run some lights, and maybe do one load of laundry every three or four days (but it would need to be sunny for all those winter days). In summer there would be more like 6.5 kWh available per day. Brent and Erin obviously needed the Pika to even out power production over the course of the year.

The Pika engineers had been working on a solution to just this problem, and wanted some test sites close to their southern Maine production facility. We almost got one of these for the campus, but the idea fell through the cracks of various personnel and sustainability plan changes. Getting one for Brent and Erin's farm was a great opportunity to make up this deficiency, and I was pleased that my students and I could be of help.

This first shot, although out of sequence, shows the overall layout of the site just prior to lifting. This is a tilt-up tower, and a gin-pole and winch arrangement is used to get it in position. Here the main tower is up on blocks and sawhorses, while the gin pole is in the proper position for the lift.

Here's the arrangement at the top of the gin pole, where a heavy duty lifting bracket transmits the force from the winch cable to the main tower guys. This tower was made by Renewable NRG Systems of Hinesburg VT. This company has been a great partner for the college over the years. Long ago they trained me in met tower work, and I've passed the knowledge on to multiple generations of SEM students. 

The tower itself was an older model 40 m RNRG tower, and was donated used to the college's wind study in 2009, if memory serves, by a different company, Competitive Energy Systems. By 2014, it was too short for today's taller wind systems, and thus obsolete and surplus to requirements.

A two-to-one mechanical advantage pulley system is used to increase the lifting power of the winch from 10,000 to 20,000 pounds.

Threading the winch cable through the pulley system.


The winch and winch anchor. We used screw-in rock anchors, there being plenty of shallow ledge on this site. This necessitated the rental of a large compressor and hammer drill, a heavy expenses, but one which will pay off in longevity and security of the anchors. Each anchor can accept up to 27,000 pounds.

An eight foot-step ladder was sufficient to vector the lifting force of the winch to a direction suitable for raising the gin. Heavier gin poles would require a second or "mini-gin."

Detail of the base or hinge plate. The gin is hinged above and behind the main tower hinge. Brent poured a concrete slab to prevent shifting of the base plat over years of use.

A cold rain hindered progress. The sensitive electronics of the turbine head needed to be protected from this.

The blade assembly ready for installation. These blades are specially designed to reduce turbine noise.

These plastic keeper bolts (under the paper) prevent damage to the slip-rings and other components through premature rotation. The yaw bearing sits above (to the right in this picture) the threaded metal cuff in the upper left.

The motherboard, showing the 12 gauge UV protected connector wire (which runs all the way to the house) and slip rings (in the see-through plastic puck at the center)..

The shroud that covers the electronics.

Assembling the blades to the turbine head.

Brent admires progress so far. But the worst is yet to come.

Torque-loading the blade nut, a "lefty-tighty" left hand thread. It took a moment for us to realize that this torque wrench design doesn't work for left hand threads. We improvised by tightening Tony's Subaru lug nuts to the required 60 pounds feet, then using that same muscle memory to calibrate the same amount of torque to the turbine head. Note to Pika: Order a left-hand torque wrench.

Assembling the vane.

Raising the main tower. This part takes a long time because you need to adjust the guy tension every few feet, to make up for the uneven height of the side anchors.

A good shot showing the additional curve we deliberately gave to the main tower. This is to allow for the additional elasticity of the upper guys compared to the lower. They are the same diameter cable, but longer, so there's more elasticity. In the end we put in too much of a curve and had to take it out later while trimming the tower.

Shifting the load from the gin-pole to the main anchors using RNRG's specially designed  come-along winch. And yes, I am holding my child. Little Roo had to accompany me on this expedition because mommy was at the dentist that day and didn't want to break her appointment (and be forced to wait two months for a new one). I stayed out of the line of fire and primarily gave instructions and advice.

Brent puzzles out the come-along. Notice the winch wire is loose. The weight of the gin pole is holding the main tower in position, because the overall center of gravity is now on the gin pole side of the hinge. To manage this, we always make the rear tower guys a little short, so that the tower stops gently before it slams "over the top."

And the final effect. You can see the power production here. We'll take a field trip out to this site during this semester's physics labs.

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