How a Wind Power Assessment is Completed
The information presented on this page will guide you through how a wind power assessment tower is assembled. Brief overviews will be given for each step in the assembly process. Also included on this page is an explanation of how data is collected from the tower and analyzed to determine the potential of a site for a wind turbine.
Towers
The two types of towers used for this project are NRG Systems Tall Towers. One tower measures 20 meters in height while the other tower measures 30 meters in height. For the full tower manual you can visit the NRG Systems Website. All pictures in this site are taken from the NRG Systems Website.
Installing the Anchors and Baseplate
The anchors assist in raising the tower and holding it in place for the duration of the data logging process. An appropriate spot for the base of the tower is chosen by the Rowan Clean Energy Team and suitable distances for the placement of the anchors are measured off from the tower base (42' for 20m tower and 60' for 30m).
A post hole digger is used to dig down the initial 10 inches for the anchors. The anchors are then turned into the ground by hand using a crowbar which is fed through the eye of each anchor. These anchors will be the main support for this tower over the next year and it is extremely important that they are firmly entrenched into the ground. This insures that there is no possibility of the anchors being pulled out during periods of severe weather. The anchors are turned until only about six inches of the anchor remain above ground. This drives the anchor approximately 4.5 feet into the ground, as shown in the figure below. Four of these anchors are installed forming a diamond around the base of the tower.
The next step is to assemble the base plate of the tower. This assembly is performed by simply bolting together each of the two sides of the base plate to the bottom portion of the base plate. Once assembled, the long foot of the base plate and a grounding road are driven into the ground. These two items are driven into the ground to prevent the tower from sliding during the raising period. The base of the tower can then be bolted to the base plate and the rest of the tower can be assembled.
Attaching the Tower, the Guy Wires, the Gin Pole, and the Anemometer
Once the tower base is attached to the base plate, the remainder of the tower is put into place in accordance to the diagram from the manual. Individual poles slide onto the preceding pole and guy wire attachment plates slide onto the appropriate poles. A figure of the raised tower is shown below to demonstrate how the guy wires and poles will look when they are all fitted and attached. With the tower and guy wires resting upon the ground, the wires are clipped off at the appropriate length. The guy wires will form multiple triangles with the tower and the ground after the tower is raised, as shown below. With the wires at the appropriate lengths, the anemometer and wind vane can be attached. These two instruments are attached to the top of the tower along with the lightning rod using hose clamps to hold them in place. Wires are lead out to the bottom of the tower and attached to each of the guy wires with pull ties, and the data logger box is left near the base of the tower until the tower is ready to be raised. At this point the sides guy wires are attached to there appropriate anchors and then the gin pole is ready to be attached. The gin pole will be used later to hoist the tower off the ground with the help of the winch. The gin pole is assembled by sliding the individual gin poles into one another, as was done with the tower poles, and it is then attached to the base plate as shown in the figure above. The guy wires on the side of the tower where the winch will be set up are then attached to the top of the gin pole.
Winch Setup and Raising the Tower
After the tower setup is complete, the only step left would be to set up the winch and raise the tower. The cable on the winch is first let out and attached to the top of the gin pole. This is shown in the figure to the left with the gin pole laying on top of the tower. The gin pole is then lifted by hand so that it is perpendicular to the tower laying flat on the ground.
With the gin pole in the air the tower is now ready to be raised. The cable on the gin pole is reeled in, which brings the gin pole towards the ground and at the same time, raises the tower along with it. After the tower begins to lift off the ground the wind vane is set so that it is calibrated to true north. The tower is continually raised while making adjustments to the guy wires as necessary. Once the tower has been raised to approximately an 85 degree angle, the guy wires are removed from the winch and attached to the anchor on the winch side of the tower. From there, the tower guy wires are adjusted by hand in order to obtain as close to a 90 degree angle as possible and the data logger is then mounted onto the tower. At this point the construction of the tower is complete and the data collection has begun. Examples of previous tower raisings are shown below.
Data Collection and Analysis
Collecting the Data
Once the tower is up and collecting data, Rowan Engineering Students will gather this data every two week. This is performed as a check in order to insure that the data is being collected properly and in order to give a preliminary assessment of the potential for a wind turbine to the customer. Two different data loggers are used for this project to continuously collect data for a one year period. These two loggers are the HOBO Micro Station, which is used at the Bayshore site, and the NRG Systems Wind Explorer which is currently used at both the Neptune and Eachus sites. The only notable differences between the data loggers is that the HOBO logger collects the average data over five minute intervals and the NRG logger collects the average data over ten minute intervals. The data is downloaded using the appropriate software that comes with the logger and is the then exported into a spreadsheet. From the spreadsheet, values are easily accessible for the necessary equations that will complete the assessment.
Analyzing the Data
The final step in calculating the potential for a wind turbine at a particular site is now only to plug the data obtained into a few simple equations. Initially, the average wind velocity is found over each hour from the data collected and values are then chosen for both coefficient of the terrain and the various power capacities of the wind turbines. After this is completed, the velocity at different tower heights can be determined using the formula:
where Vo is the average velocity found over each hour in the data readings, Ho is the height of the tower that the data is being collected on, H is the height at which you would like to know the power output at, and is the coefficient of the terrain. Once the velocity for a tower of any height can be obtained, values given in the manufacturer's specifications can be used to find the power output at any height that you wish. With the power output known the payback period can be found dividing the initial cost of the wind turbine by the power output multiplied by the local cost per kWh, this is also shown in the following equation here:
