As the previous test was at mast height, confirmation from SkySails of the reference height would be welcome, as for the kite area for both tests. See also the last link.
Could the reference height be the middle of the pattern height, in order to match the reference height (see just below) of a conventional wind turbine?
Wind Speeds
Reference / Rated wind speed
Definition: Minimum wind speed at pattern trajectory height at which an AWES’ rated power is achieved in the case of steady wind without turbulence.
Notes:
IEC 61400-1: “minimum wind speed at hub height at which a wind turbine’s rated power is achieved in the case of steady wind without turbulence.”
Default: When not explicitly stated when referring to wind speeds, one can assume it refers to the rated wind speed.
One point on the power curve (see graph in Power Curve)
Basic parameter for wind speed used for defining AWES classes
Can be measured with LIDAR and is standard. ERA5 provides wind speed at 100m as a standard output. Good data availability and comparable to conventional WTG hub heights.
The other great thing about this curve is they are starting production just above 5m/s at their kite reference height. At 10m above ground that’s going to be lower than the ~4m/s we expect an onshore wind turbine to cut in at.
4m/s cut in at 10m AGL was one of the key requirements we had set for the recent MVP development we tried at Windswept. @tallakt did you say this represents a new power/weight record in AWES?
Yes, this is what the additional information from the previous test suggests.
And everything suggests that for the current test the height reference is the pattern height, while for the previous test, the reference height was the mast height (10 m). This would make a huge difference to the power curve.
But one point tempers this assertion considerably: in the previous test, the wind speed measured at mast height was around 12 m/s, which is not far from the 15 m/s top speed of the current curve, and this after decreasing the progression of the said curve.
Nevertheless, I still find it disturbing that the 92 kW with a wind speed of 12 m/s measured at mast height (10 m) fits perfectly into the current curve with a wind speed measured at pattern height.
We have shown AEP prediction in this paper: WES - Clustering wind profile shapes to estimate airborne wind energy production
Here, the operation of the AWES was optimized for each wind speed, using characteristic vertical wind speed profiles, and their probability, derived from a clustering method.
This approach is obviously site-specific. It also demonstrates that a power curve of a specific AWES will look different at different sites.
No I wouldnt stretch it that far. Just heard someone mention that power to weight even for this concrete installation surpassed that of a HAWT. Though we should wait for real data before drawing any conclusions.
Though, I guess this would anyways be the best «verified» AWE anything, as this is the first one to be externally verified?
Could it be the same curve as in the figure 15? If yes, the deduced efficiency would be far higher if the reference height was the pattern height instead of the mast height as specified in the figure 15, given the wind gradient as suggested in the text (see the quote on the commentary on which this post is based).
Wow, this “news” is already over a year old? Seems like just the other day…
I’m just gonna say, we’ve become used to celebrating any mundane detail of “progress” in airborne wind energy. with a press-release, and great fanfare (from the fans - most people couldn’t care less).
The first question asked of anyone with a new (advanced?) wind energy device is “Where is your power curve?”. Usually they don’t have one, and bristle at the implication that they should even have a generator, let alone deliver any power, let alone measure it!
In this case, a verified power curve seems long overdue, since they were supposedly selling finished systems out of their factory 5 years ago. I’d say Pierre has scrutinized this one as much as anybody, and his question about the height of the anemometer is appropriate - that’s a corollary to that first basic question of even having a power curve.
On the one hand, anemometer placement for a power curve is normally taken at hub height. On the other hand, I could see a rationalization for airborne to place the anemometer at the hub height of a conventional wind turbine of similar output. Normally though, AWE people like to pretend regular wind turbines don’t exist, so they can pretend islands hooked on diesel do not have the option to simply install regular wind turbines, rather than pretend an airborne system that can only operate occasionally, with full-time human supervision, is their only option.
