Recipient Organization
EWINDSOLUTIONS LLC
30678 SW ORCHARD DR
WILSONVILLE,OR 97070
Performing Department
(N/A)
Non Technical Summary
The tether and power generating ground station,are the focus of this proposal. Both these systems have challenges that are unique to the airborne wind energy field. First is the selection and design of the tether itself. This includes the material (e.g. nylon, steel,or composite) and whether to weave in electricity-transmitting wires between the ground station and the flying craft (which would increase its cost and diameter). These wires would be used to power the electronics on the flying craft and facilitate communications with the ground station. All these choices have trade-offs,however. Specifically, the tether will be the main source of aerodynamic drag in the entire system and, thus, one of the key limiting factors in the quantity of electricity produced. The other key system is the ground station itself. This includes several components: the drum and tether management system, electrical generator,and electrical systems that convert noisy renewable energy into smooth, reliable 120V AC for equipment or home use. Conveniently, these converting electrical systems are relatively abundant and a set that fits our exact needs is either commercially available or created with minor modifications. The tether management and electrical generator, however, are much more complex and not commercially available. The tether management system, a combination of custom hardware and custom software, must reliably:-Maintain a desired tension on the tether -Monitor tether tension, reel-out speed, tether-to-ground angle, length deployed, etc. -Maintain reel-out speed to a specific value determined by the wind speed -Monitor and maintain airspeed of the flying craft during launch/landing -Reliably guide the tether onto the drum without crossing layers In aggregate, this creates a complex system of mechanical controls, sensors and software that must work together to maintain consistent flight, maximize power generated, and minimize wear on each component. To maintain consistent tension on the tether requires constantly monitoring and adjusting for differing pull strengths from the flying craft because of changes in wind speed (gusts, lulls) and different aerodynamic lift at each point of the figure-8 flight pattern. To maximize power generated, we do not want any spring or physical braking system to smooth out the tether tension because these forces create drag and friction, wasting energy. Instead, we will use the electrical generator itself as the resistance and rewind motor. A generator and motor are the same physical system, differentiated only by whether electricity is flowing into or out of the device. Therefore, by monitoring the tether tension and reel-out speed, the tether management system can adjust the electrical load (resistance) of the generator to control both variables. The system can also use the generator as a motor to rewind the tether each cycle. In short, by constantly monitoring and maintaining several variables of the system, the tether management system can maximize power generated by clever manipulation of the electrical generator. It must also perform all these tasks flawlessly over the ten-year lifespan of the device while exposed to degrading UV radiation and seasonal weather. Ensuring this level of accuracy and reliability over a decade is a complex engineering challenge. Finally, the electrical generator is novel because it represents one of the biggest advantages our airborne wind energy system has over traditional wind turbines and other airborne competitors. Generators on top of large towers or that are airborne have a premium placed on size and weight for obvious reasons. As a result, they are built from exotic, magnetic materials (e.g. metal-doped ceramics) that are extremely delicate and expensive. They are also physically small. This feeds directly into the fundamental trade-off in generator design: a physically small generator equals higher revolution speeds (e.g. 1,500-2,000 revolutions per minute (r.p.m.)) while a physically large generator equals lower revolution speeds (e.g. 50-80 r.p.m.). For traditional wind towers, this is a double blow because the input speed of their massive bladesisonly a few r.p.m. Thus, they must insert a gearbox to increase that blade revolution speed to match the speeds required by their physically small generator. These gearboxes not only decrease the efficiency of the system (a 3-10% loss is considered typical for commercial gearboxes) but are also the most likely component to fail, typically lasting seven years in a twenty-year turbine lifetime (Townsend, 1991; Windpower Monthly, 2005). To add insult to injury, they are also approximately 13% of the cost of the entire wind turbine (EWEA, 2009). This combination of small, expensive generator and expensive, inefficient gearbox is required by the need to make the system physically small and lightweight to fit atop a tall tower. Our airborne wind energy system has none of these constraints, however. Because we place the generator on the ground, its size and weight are relatively meaningless (within reason). In fact,becausethe ground station will likely have to be weighted or secured to the ground to ensure the flying craft does not pull it downwind, a moderate amount of extra weight is actually a minor benefit. This ability to physically scale the generator to meet our input and output needs gives us a large efficiency and cost advantage over traditional wind turbines. Becausewe also have a low r.p.m. input, instead of needing a gearbox, we will simply make the generator larger to accommodate the lower r.p.m. source, immediately saving money, complexity, and maintenance. In our system, the generator will be roughly 4-5 feet across and weigh approximately 250-300 pounds. This larger size has several beneficial knock-off effects as well. Electrical components are larger, more robust,and actually cheaper than their miniaturized versions. Also, we do not need the fragile, esoteric magnetic materials, relying instead on either traditional high-strength rare-earth magnets or electronically controlled electro-magnets. The drawback of our generator is that fact that it currently does not exist. Commercially available electric generators are almost universally skewed towards being physically small with higher r.p.m. Fortunately, the physics governing generators is straightforward and we have already built several functioning prototypes. In summation, designing and building our own generator will decrease the economic risk of rare-earth magnets and greatly decrease its cost in exchange for the increased burden of more complex research and design task. In addition to the flying craft, tether,and power generation system, there are secondary technical components that must be developed and incorporated into the final system before it will successfully meet the needs of small farmers. These include: automated launch/recovery with the ground station, ground station/flying craft communication, rectifying and smoothing variable renewable power, flying craft onboard power and electronic controls. While none of these are trivial development tasks, we believe they are all addressable based on the experience and expertise of other emerging fields and industries. Most applicable are the burgeoning field of unmanned aerial vehicles research and the accompanying plethora of private drone companies. For example, a number of drone companies have already developed methods for drone launches and recoveries (Insitu, 2014; Honeycomb, 2014).
Animal Health Component
25%
Research Effort Categories
Basic
25%
Applied
25%
Developmental
50%
Goals / Objectives
This Phase I project is focused on the design and development of the power generating ground station. This comprises the tether and its aerodynamic effects on the system (including the FAA mandated safety flags), as well as the mechanism and software that will manage the tether and control the tension, reel-out speed, and rewind, to maximize the return on investment for our farming customers. Our system is designed around the needs of small farmers in rural communities. Therefore, the goal and emphasis of this project is to produce a smaller system (11.6kW nameplate capacity) that will, with our predicted capacity factor, produce close to the electric energy used by the average small farm. We have chosen to place the generator on the ground, flying a rigid or semi-rigid winged craft in a crosswind pattern, utilizing a single tether, flying below the current FAA limit of 499 feet (150m) above the ground.There are three main components to our airborne wind energy system. First is the novel flying craft itself. Our design choices (crosswind flight, ground generation, ridig to semi-rigid wing) have created the need for a novel, complex flying craft. Its development is progressing quickly under the support of a previously awarded Phase II grant.The tether and power generating ground station are the focus of this project. Both have challenges that are unique to the airborne wind energy field. The ground station, which includes the drum and tether management system, the generator and electrical systems that convert noisy energy into smooth, reliable 120V AC. Conveniently, these converting electrical systems are realtively abundant and a set that fits our exact needs is either commercially available or created with minor modifications. The tether management, a combination of custom hardware and custom software, must reliably: a) maintain a desired tension; b) monitor tether tension, reel-out speed, tether-to-ground angle, and length deployed; c) maintain reel-out speed to a specific value determined by the wind speed; d) monitor and maintain airspeed of the flying craft during launch/landing; and e) reliably guide the tether onto the drum without crossing layers.The goal/desired outcome of this project is: create a complex system of mechanical controls, sensors, and software that must work together to maintain consistent flight, maximize power generation, and minimize wear on each component.
Project Methods
Evaluation:We will use a previously completed aerodynamic analysis of the tether to select a tether material and diameter, and design the safety flags and lighting. We'll design and build the physical components of the tether management system. This includes sensors, tether guides, and temporary tension control mechanisms. Build a testing apparatus that will simulate the flying crafts force by pulling on the tether. Design and program the software control components of the tether management system. Combine with the physical components to create a prototype tether management system.