Turning kites into kilowatts

The UK gets almost 30% of its energy from renewable sources. But that means that over two thirds still come from non-renewables, like coal, oil and gas. And the signs are that we need to improve our act quickly, because time’s running out to cut carbon emissions. So a new way to harvest energy from the wind sounds very attractive. What Skypull have invented is a system that uses a kite - equipped with drone motors to enable it to be controlled - which flies much higher than the average wind turbine; and by pulling on its rope, it generates large amounts of electricity on the ground. Chris Smith spoke to Edgar van Nunen, part of the Skypull team, to learn more…

Edgar - We want to make a difference to energy transition to renewable energy to replace fossil fuel energy use, and that is a big problem. Fossil fuel use is growing twice faster than renewable energy production.

Chris - So what's your solution?

Edgar - We are developing a system producing more energy but also doing that in more locations. Our system works with a drone that operates fully autonomously at altitudes up to five times higher than wind turbines reach.

Chris - So we must be talking one hundreds of metres half a kilometre to a kilometre up then

Edgar - About until 600 metres, is that what we're planning. With that we're staying under the altitude of commercial air traffic but at the higher altitude there is far more wind available across all of Europe.

Chris - So explain to me how this works then you're saying it's a drone aircraft that's going to generate electricity from wind. How?

Edgar - Correct. So it's a drone it takes off from its platform on the ground station which has the generator so we have two elements. One is the drone and the other a ground station with generator. They're connected by a tether or a rope if you like. And it functions as a kite. So it goes up with motors but done with minimum wind speeds to sustain the drone in the air. Maybe you know when you were little; the kite stays in the air you can steer it and actually when you take a little bit bigger kite like some people do like in sport kiting it becomes quite a bit of force and you feel it in your arms. Now if you make that a little bit bigger you can actually say hey that force that I feel I can do something with that energy and that's what we do. We harvest the kinetic energy of that wind and it is exercised on the tether which is connected to a winch on the ground which in itself is connected to a generator. So by going up we are generating electricity from lift force of our drone which is operating without motors of course which are pulling the tether and driving the generator on the ground.

Chris - This is ingenious so basically the thing ascends. It's being pulled up by the wind and you let the cable out which is generating electricity on the way up. Then what you put it into a dive so it loses altitude again and you reel it in because it's obviously not going to take an energy to reel in the slack tether as it comes down and then you just keep repeating this in cycles up and down and every time it's on an up cycle it's pulling hard on the string and that's generating electricity.

Edgar - Exactly that's how it works. We call it the yo yo cycle so like a yo yo it goes up and down. We can also like you do in sailing you move it partly out of the wind then you're only let's say taking part of that power from the wind, so you get into a range where from a low wind speed, enough to sustain the drone in the air, to a very high wind speed can be handled by the system.

Chris - How big is this thing?

Edgar - So our current prototypes are very small still that is proving the concept. So we're talking about one metre wingspan and kilowatt scale production.

Chris - So despite only being a one meter across kite effectively that's generating electricity at the rate of a kilowatt?

Edgar - Potentially up to four kilowatts.

Chris - That's a lot.

Edgar - It is. And the next level that we want to develop to really demonstrate in the market that this works, that it is efficient, and that it is safe, which is a drone plan at a six meter wingspan. Now a 6 meter wingspan, we talk about a 60 kilowatt system. The ultimate plan is to go to a megawatt scale.

Chris - Will this be deployed as, in the same way as we have a wind farm, or we have a solar farm with a big array of generating entities. Would you have an area of the country mapped out and you would just have each of these on its own footprint so that there's no risk of tangling and that kind of thing. I could imagine this could become a disaster; I've done kiting and the number of tangles I've gotten into has been tremendous. So how do you surmount that? Is it that you have to have an area that you exclude other drones from so they don't fly in to each other.

Edgar - There's always a risk. Now it's about how big or how small that risk is. We develop to aeronautical development standards. That means that there is a risk of one in 10 billion or something like that.

Chris - What about noise? Because people are very concerned with the present generation of wind turbines about the noise they make.

Edgar - It is quieter when we're operating in the air it is travelling at about four times the wind speed. When you talk about the turbine blades they go up to 40 times the wind speed, and that's what's making the noise so wind noises we don't expect. We do have a noise at takeoff and landing. We talk about motors, electrical motors to put for a megawatt system 2 tons of weight into the air, but you only have it when it goes up and when it lands and that's maybe once a day, once a week, who tells? If the wind is enough it just stays up there without noise.