Developing A Ground Station For Airborne Wind Energy System

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