If there's any country where you'd expect scientists to discuss windmills, it would be the Netherlands. Except maybe not flying ones.
Still, 'Airborne Wind Energy' (AWE) really was the subject matter of a conference in Delft this week. Engineers discussed the latest advances in harvesting wind energy at altitudes of a couple hundred meters, without having to build expensive tall concrete structures. One of the potential advantages is the fact that at the higher you go, the stronger, more homogenous and more reliable winds get. Not to mention the added bonus that winds twice as strong contain eight times as much energy.
One of the highest profile proponents of AWE was the first Dutch astronaut Wubbo Ockels (1946-2014), who after his space career became professor at the Delft University of Technology. For years he worked on an invention called the 'ladder mill'. This consisted of a set of wings mounted in an escalator-like configuration. Ockels could prove this contraption could stay airborne, but he never found a way to make it take off.
This week's conference was the sixth time international experts in this field gathered. They came - among others - from the US, Canada, Australia, India, Germany, France, Belgium and the Netherlands. They were employed by scientific institutions and by companies from tiny startups all the way up to Big Google. Google in 2013 acquired AWE pioneer Makani and is now a leader in the field. Google recently upgraded its prototype from 9 meters wingspan to 26, and from 30 kW to 600 kW. Another leader is Dutch high tech company Ampyx Power, which was founded by Delft alumni and builds on Ockels's heritage.
There are interesting differences in technology between one team and the next. For instance, Makani's prototype has generators on board, like propellor motors in reverse, and sends power down via conducting wires. It's very much a windmill which isn't mounted on a pole. Ampyx uses a glider plane they call the PowerPlane, which pulls on its tether and sets a generator on the ground in motion. The whole field is still looking for the cheapest, most efficient and most durable way to make AWE work.
Another interesting difference is what airborne energy harvesters actually are, in terms of regulations. Most present themselves as kites. Ampyx'PowerPlanes are actually registered as (unmanned) airplanes. Says Jaap Bosch from Ampyx: 'We decided, after talking to the authorities, that if it looks like a plane and behaves like a plane, you probably should call it a plane. We want to comply with the safety regulations of air traffic. This means a lot of paperwork and cost and this weighs heavily on a startup that has no revenue yet. But if some accident happens anywhere in the sector and the rules are tightened, others will have to redo their homework but we will be prepared.'
Time will also tell where we'll find airborne energy harvesters by then. Offshore is a possibility but Ampyx is also working with the Dutch Forestry Management to find suitable locations where nature conservation meets sustainable energy.
Herbert Blankesteijn is a technology journalist from the Netherlands who has written for many prominent Dutch newspapers. He presented and directed television and radio programmes and has 10 books to his name. Herbert is interested in nascent fields such as 3D printing, drones, robotics and the private space business.