Another point: there are losses due to the irregular power according to the place of the wing within the wind window. The sound varies during the figure as we can hear on the videos below.

How much time do you have to complete your project? You have chosen a very complex question, and it will take some time to locate key references scattered in the domain literature.

Be sure to calculate square-cube and other parasitic up-scaling factors, which are predicted to be starkly evident between Makani’s 30kW Wing7 prototype and the M600 prototype. Its quite possible the M600 is netting very little power due to looping cycle phase losses, and high energetic cost of just maintaining its large mass in flight.

. Thank you for your help brother. I have another question related to this topic that why we can not use blade element momentum theory beyond induction factor of 0.5?

You’re most welcome, Saqlain. Given the short time frame, it will be very hard to produce a correct estimate. Blade element momentum theory as such omits many critical parameters, including the parasitic effect of maintaining high mass powered flight.

The 600kW claim has limited objective public data basis. Makani has not provided key data, like how much platform and tether weigh, nor the tested thermal limits of their larger motorgens, and other electrical losses. They likely would have shared power curves that met optimistic claims.

There is one source of good public data; Videogrammetric parameters, to derive flight pattern scale and time values. A sufficiently deep video analysis, including the audio track and wind-velocity clues, in principle suffices to derive close net power-out estimates.

Why are there no tested M600 power curves publicly supplied by Makani? Why no Norway Mishap Report either?

It seems the likeliest reason these numbers are secret is that the M600 is not delivering enough power across the lower wind range, due to predictably severe scaling law limits on its architecture. A similar logic of investor/public-relations damage-control seems also to explain the missing mishap report.

Surely TUDelft has an informed opinion about what hidden M600 data would reveal. We should all press for full disclosure, on academic and safety culture grounds. Are any of the AWEurope folks under Google NDAs?

Hi @rschmehl,
I propose to introduce the ratio power / land and space used which is more realistic than the usual power/wing area ratio.

The initial question was about M600. Its tether length is 440 m, being also the radius of the minimal covered land area of 0.6 km², leading to a density of 1 MW/km² with difficult or no secondary use due to safety issues, that compared to about 8 MW/km² for the current wind turbines with possible secondary use.

By supposing that 600 kW is really reached (is there a power curve?), a farm of kites of this type would multiply the issues.

As a result IMHO architectures maximizing the land and space used should be more investigated.

I also think that the power-to-surface-area-used ratio is a useful metric, especially once AWE systems have reached higher TRLs and are operated in relevant environments. Only then we will have more certainty about the surface-area-used parameter.

The power harvesting factor \zeta=P/(P_wS) that is now often used in theoretical studies [1], was introduced as a result of dimensional analysis. It uses the wing surface area S because this is the only area measure that is constant for an AWE system. Other than wind turbines, where the blades of the rotor are always sweeping a constant area A=\pi l_b^2, an AWE system will not necessarily harvest from a constant swept area. This is also the reason why it is not straightforward to formulate the Betz law for AWE systems, which has been the subject of a number of recent studies.

While we can now determine the power output and annual energy production (AEP) of AWE systems with reasonably good accuracy, both by measurements as well as by computational simulations, the surface area used by AWE systems is a less tangible parameter. It will be influenced by the specific type of AWE system (e.g. rigid wing vs flexible membrane wing), operational safety characteristics and regulations. I think that you will agree that there is little data available on this. Also the cost of this surface area needs to be taken into account (offshore vs onshore). Your estimate of drawing a circle with the maximum tether length around the ground station is only a first guess, which will probably be contested by industry. In recent publications [2,3] about flexible wing systems we have introduced a spacial layout of kite parks that is requiring decidedly less space. See, for example, Fig. 4 in [2].

But I do agree that AWE architectures maximizing the surface area by concept used should be investigated more thoroughly.

References

R. Schmehl, M. Noom, R. van der Vlugt: “Traction Power Generation with Tethered Wings”. In: U. Ahrens, M. Diehl, R. Schmehl (eds.) “Airborne Wind Energy”. Springer, Berlin Heidelberg, 2013. doi:10.1007/978-3-642-39965-7_2. Preprint accessible as pdf.

V. Salma, F. Friedl, R. Schmehl: “Improving Reliability and Safety of Airborne Wind Energy Systems”. Wind Energy, in production, 2019. doi:10.1002/we.2433. Preprint accessible as pdf

P. Faggiani, R. Schmehl: “Design and Economics of a Pumping Kite Wind Park”. In: R. Schmehl (ed.) “Airborne Wind Energy - Advances in Technology Development and Research”, Springer Nature, Singapore, pp. 391-411, 2018. doi:10.1007/978-981-10-1947-0_16. Preprint accessible as pdf

Highest “power-to-surface-area” is a power-kite design trap of high wing loading. It especially does not scale because wind velocity remains constant, while scaled-up stall speed increases, and turn-rate decreases. Highly wing loaded wings are not crashworthy. In AWE such wings will take decades to reach TRL9 MTBCF statistics (<1 mishap per 100khr). Wikipedia-

“…an aircraft with lower wing loading will be able to take off and land at a lower speed (or be able to take off with a greater load). It will also be able to turn at a greater rate.”

Guessing that TUDleft signed Google-Makani NDAs, locking them into helpless acquiescence to the withheld M600 Mishap Report and power curves, unable to champion open M600 data.

Highest power-to-mass remains the top number in aerospace generally, and will prove so in AWE. The M600 scores far poorer than any power-kite in this most predictive parameter.

A heuristic approximation of M600 power is that hover and vertical climb power-out is approximately equivalent to max power-in, under similar electrical-thermal limits. Comparable power-out/in RPM data may be evident from audio track. Has anyone found accurate test wind velocity and mass numbers for tether and aircraft? Its likely prior mass estimates were overly optimistic.

Also, “rated power” is a bad metric if the wind velocity basis is poorly probable. WECS developers have often simply raised the rated power wind velocity to fit a chosen power number.

The initial 9m/s estimate was years before actual M600 testing, and now real data exists (but is secret; as unfair business practice if Google is wrongly believed better in AWE). The hidden picture may be cut-in around 9m/s, and rated output now at rather higher wind velocity. Poor M600 low-wind performance may hide in simply motoring around the loop. The audio signal can reveal struggling in the upward phase.

Here is a more refined estimation heuristic-

Look up max power rating of the M600 motorgen, multiply by eight, then start subtracting parasitic factors (drag, mass penalty, electrical loss, overheating, etc). This may not give precise wind velocity, but does give a certain top power limit that is almost certainly being risked in testing, and may have caused the crash.

If M600 aerodymamic and motorgen estimates correspond, that’s good, but not very realistic. In real wind, that varies a lot moment to moment, the system may have high loss due to motoring through lulls and popping up to chase transient gusts. Practical estimation of M600 power capacity must account for borderline conditions.

aslam o alaikum saqlain .
m also working on it let me clear some of your points as for as i studied.

we can mesure height of the kite by mesuring the tether lenght and the elevation angle.
2.second point has also same answer by knowing height we can see the velocity of wind at that height and i have also a formula for that.
3 and 4 th point m looking for the answers but could nt find anything proper trying to search like you iff u have any information about that please tell me also.
03063443228 whatsapp nbr we have a same project we can help each other . thank u

@PierreB .
i am a student of M-PHIL electrical power. first of al thank you for such data and comments from which i could get basics of the kite energy .
brother you are requested to please help me in some problems that are in this given paper.

there are two powers . LIFT and DRAG . Did we have to calculatre both of them and after adding them we will get overall power? because one is pumping kite power and other is on board generator power

in drag mode if we see in this paper in equation 29 what is (Ak(area of what) )he use a word of area is where from we will get this area . is it the area of onboard generators or overall area of generators and kite?
3.why we put a=0 in that last equation for drift power ?
4.in the LIFT power output equation is there any will be difference between that lift to drag ratio for both lift power and drag power ? if that as you early discussed difference of 1/3 ?

what will be the value of “a” in the lift ouput power .?
plese help me brother regarding all of these question i will be ery thankfull to u.