ENERGY EXECUTIVE MAGAZINE
Written by Brian Salgado
Dakota Turbines has developed an efficient wind turbine system.
For many startup companies in the fledgling wind energy industry, patented technology and parts are considered innovations that must be protected. However, Dakota Turbines considers its patents par for the course in its pursuit of market share for its parent company, Posilock Puller Inc. “There are many aspects of the designs of both the turbine and inverter that are being patented, and several other technologies that probably could be patented,” says Keith Monson, sales manager at Dakota Turbines. “That would give an indication of significant innovation in both major parts of this project. Internally, they are thought of less as being innovative, as they are strategic in the development of the products.”
Dakota Turbines started as a new product development discussion at a weekly meeting of the Posilock Puller Inc. management group in 2006. Discussions over a few weeks led to a design concept that became the foundation for the present day generator. According to Monson, that basic design concept then transitioned into R&D on the 18 individual coils that make up the stator half of the generator.
“Early testing was done by fixtures mounted in CNC machines,” Monson says. “Various wire sizes, geometrical shapes, and a myriad of options were tested before further work or design was done on the physical structure that would become the actual generator.” Once the shape and size of the coil was initially determined, Monson, says, the 3-D modeling of the generator itself started to take shape in mid-2007. The original concept of two disks, the stator and rotor sitting on the same axis, was the basis for the first 3-D model.
“The first two prototypes included what we coined the ‘Sliding Stator Technology,’ which allowed the coils to be moved into or out from between the two rows of magnets,” Monson says. “That allowed the rotor to initially start turning with only the friction of the bearings as drag, and then once spinning we could introduce the coils to the magnets to start producing electricity. “Using this technology, we were able to put electricity onto the grid at a wind speed of less than 3 miles per hour,” Monson adds.
Once the generator itself was assembled, it was tested on a trailer using the power take-off of a farm tractor for power. Utilizing conventional kitchen stoves for a load, burners and ovens were turned on and off to provide various load scenarios in the testing process. Once this initial testing was done the turbine assembly was designed for a downwind turbine and installed on a guyed, self-raising pole tower. The company made the blades used on the first two prototypes using a mold from a 1970 blade design, according to Monson.
Monson also says parallel to this effort was the design and manufacture of a single phase inverter, as no off-the-shelf inverters were available in single phase. “Over the course of this project, the inverter development proved to be by far the most challenging part of the project,” Monson adds. With the prototype inverter attached to a sheet of ¾-inch plywood, the first prototype turbine was mounted on a tower and flown in a grid-tied configuration for the first time in winter 2007-08.
“That machine was flown long enough for us to create a rather long list of other improvements that would be required on the next version,” Monson says. “Prototype 2 was an upwind machine with pitchable blades and active yaw. “This machine was also flown for several months and again led to the need for several refinements to be implemented,” Monson adds.
By the spring of 2010, the inverter had migrated to a ULlisted enclosure; the turbine assembly was considered of commercial quality; and fitted with a commercial blade, a turbine was again flying at the test site. “The two largest hurdles at that time were getting a new blade designed for our specific needs, and to improve the algorithms that control the yaw and the turbine itself – the software control systems,” Monson says.
In fall 2011, four systems were installed in various locations in eastern North Dakota. Other than upgrading a couple electrical components as new and more efficient models became available, the turbines and inverters continue to run as installed almost three years ago.
“Most importantly are the procedures put in place recently to test and confirm the generation capabilities, reliability and noise levels to provide the general public with a third-party certification of a system’s worth,” Monson says. “It is our goal that the test we are just starting will set new standards of efficiencies for small wind turbines.”
The experts at Dakota Turbines have learned many valuable lessons during the development phase of its products, but the most important one of all, according to Monson, is to maintain a patient approach to product testing. “The goal from the very beginning has not been to build another wind turbine,” Monson says. “The goal from the start was to build the most efficient wind turbine system on the market.” The attempt to attain those extra percentage points of efficiencies has been a large part of the reason behind what might be a longer than usual development process.
“If a future project deals with Mother Nature and the forces and variables being applied in the real world, no amount of software design programs, mathematical equations, or other logical solutions will provide all the answers required,” Monson adds. “Make the effort to test your product in the real world, over time, and deal with the issues you thought were solved.”