Airborne Wind Energy Conference Netherlands 15-16 June Part One
2015年6月17日 Dr Peter Harrop
This is the leading event on this subject: it moves around the world. AWE is the generation of electricity by flying devices in the wind, whether tethered or untethered. Almost all such projects involve tethered devices, over 30 being kites. The trend is to fixed wing kites: many start with flexible fabric but go to fixed wing - never the other way. Some are tethered aircraft that can take off and land themselves. Some make the electricity aloft but most generate it on the ground, for example by pumping action of a kite or rigid glider which generates electricity when extending, usually in a figure of eight trajectory to increase experienced wind speed, and uses energy when pulled back to start again. A few are aerial wind turbines but aerostats are out of favour. These have the wind move devices up and down tethers, the aerostat itself sometimes acting as a rotor to make electricity. Aerostats cannot take advantage of cross winds. Also out of favour are autogiros though there was one presentation on them. They have to operate at significant yaw angles reducing efficiency. The regulatory and safety nightmare of all AWE these devices was well covered in this event, the improved legislative and technical situation giving some room for optimism but they are never going to be allowed near aircraft, even in failure mode. Consequently, although they have much lower material cost than wind turbines, the overall cost often start higher.
The sweet spot for AWE is currently about 10 kW to 1 MW. You will not see the little wind turbine on a traffic sign or small boat replaced by a little kite flying a figure of eight any time soon. Optimal height is most usually 150 -200 meters to escape aviation rules and for operational reasons. Clearly it also varies depending on the technology but there is a bit of over-selling in the argument that wind speeds are higher up there because, as several speakers cautioned, this is not true on a hot or summer day. we would add that, although a wind turbine can automatically feather its blades if a severe storm suddenly hits, rapidly getting a fixed wing down safely is an issue: indeed, some may be unable to operate when a wind turbine can tolerate a high wind so their useful duty cycle may be more constrained.
The event was attended by over 200 people, only 5% being women. Apparently flying kites is a man thing. IDTechEx spoke to many of them, learning that, compared to earlier events, this one is less academic and more commercial, seeking business cases. However, some told us that it is a technology that is still an answer looking for a problem. Many believed that, so far, it is uneconomic for on-grid application and that is the main reason for some participants commencing with off-grid applications. Those where portability is valued and replacing diesel was often mentioned, though full replacement when there is no wind is problematic.
The approach varies from Makani owned by Google taking the jumbo jet approach and making an eight turbine plane strong enough to take off vertically and land when tethered by a power cable that moves a lot of electricity in both directions as required. Its M600 will generate 600 kW. This is therefore the largest and heaviest AWP implementation.
Its presenter Damon Vander Lind, Lead Engineer, told IDTechEx, "It's nice to be doing something that will be a spectacular success or a spectacular failure". He benchmarks success as competing with coal because coal fired power stations must be eliminated to save the planet. He does not expect nuclear power to be viable ever and gas should be limited to expensive top up on the grid. He sees off-grid applications of aerial wind power but it is not their objective.
TwingTec and e-Wind were companies taking an opposite approach, starting with off-grid applications competing with diesel and starting with only 12 kW output in the case of e-Wind. This is seen as attractive to farmers renting out space. 50K kWh/year is seen as 50% of a farmer's needs in the USA and there are over 200,000 of these farmers in the USA. Some farmers want it to cast the shadow of a large bird of prey to protect crops from birds. Advertising on AWE craft has been a failure as they are too small and distant.
Dr Rolf Luchsinger, Managing Director described his TwingTec lightweight, low-cost system generating the power on the ground by pumping a fixed wing. He pronounced it to be ten times more portable than the equivalent photovoltaics or wind turbine. He targets $100 million sales in a few years but he recognises that AWE is high risk and the result may be nothing. See the new IDTechEx report, Energy Harvesting: Off-grid Renewable Power for Devices, Vehicles, Structures 2015-2025