Capex of an inexpensive flexible wing like NPW

Let us take as a base an inexpensive 9.5 m² NPW sold for 223 euros (1 euro = $ 1.21).

As even a flexible wing suffers a mass penalty (less than that of a rigid wing but not negligible) as its surface increases, we will still remain optimistic by evaluating the m² at 20 euros.

Knowing that in yo-yo mode you need about 3500 m² of wing (s) for 1 MW with a wind speed of 10 m / s (including the cosine penalty and the division by 2 because of the reel-in phase), the expense is 70,000 euros per wing (s).

By being very optimistic, the production lifespan would be 1 year, or 8760 hours, knowing that the most resistant sails reach 2000 or 3000 hours of service.

Over 20 years, we therefore expect an expenditure of 1,400,000 euros, or $ 1,694,000.

That is about the price of a complete 1 MW wind turbine.

This gives an idea of ​​the way to go, the other elements not even being taken into account in this rough calculation.

The glide ratio is low causing excessive wing area needs?

For NPW the glide ratio is (just) below 3, instead of 4 or 5 for some other power kites. And as you know in the formula the glide ratio is squared.

The wholesale cost of 70 denier ripstop nylon is presently about 2.0 €/M2. The cost for the kite is therefore mainly manufacturing and assembly. I therefore think that a more reasonable 20 yr cost would be about half or 10 €/M2.

In contrast let us compare to an advanced Kitewinder system with a lifter kite of the same area. A static lifter should have increased life over a power kite and construction costs are much less. The turbine(s) will be oriented to face the wind eliminating cosine losses. This system will operate at higher wind speed due to higher altitude; say 12 m/sec with an estimated 70% increase in power. Combine this with continuous operation and I would estimate that we therefore expect a 20 yr expenditure of about €700,000 or $840,000.


Indeed NPW is a power kite, and a power kite is more solicited than a static kite, and its wear can be expected as higher.

Yes, but scaling up leads to the requirement of thicker and stronger fabrics. It is the reason why I roughly evaluated for 20 euros/m². In fact that can be more for a crosswind use, given the high constraints during operation, comprising the wearing yo-yo phases.

Basically I think your message is relevant. Another advantage of a static system is the possibility of a higher elevation angle (above 50 or even 60 degrees against 30-35 degrees for a crosswind flight) and a safer use.

A turbine lifted by a kite could be both the simplest and most promising AWES as its Power to space use ratio could be more effective, but unfortunately its potential is very low.

Perhaps it can scale by being implemented in networked systems (in order to avoid collisions between unities), using the bumper car mode, but the low potential would remain, and also it is for another topic.

The problem is that kite lift force decreases at high tether angles. We therefore require a larger area kite. Is there a source where I can find an analysis of tether force as a function of tether angle, wind speed and kite area?

This 3 m² lifter kite has a strong pull of 5-7 kg in 5 m/s wind speed at 67 degrees elevation angle.

See also on the link below then on request button:

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