A wind turbine costs about 1.000 Euro/kW. A sail is cheaper, but it has the same effect: by creating a region of low pressure, it extracts energy from a flow of air. Imagine placing the sail of a ship close to a wind turbine, so that the low pressure field of the sail augments the low pressure field of the turbine, and let the sail push the turbine, instead of the ship...
We have built 2 prototypes, one is shown below: the wind turbine used would cost about 300 Euro. It is surrounded by a shroud of 100 Euro.
The shroud increases the power of the turbine by a factor of 2.5.
In difference to the Grumman design, there is a flow of air between the tips of the propeller and the shroud - consider that the shroud is supposed to create a low pressure field. It can do that only, if air is flowing over its surface fast. But the air flow is slowed down by the propeller, of course. The same air flow, which is slowed down by the propeller cannot possibly be used to create an accelerating low pressure field over the bent surface of the shroud - you cannot successfully accelerate and decelerate one and the same flow of air at the very same time.
We have shown that also for water turbines the flow of water through the turbine can be accelerated by means of a bent surface around the turbine, in the same way as for wind turbines.
But we have also found, that the prices of conventional water turbines are simply not justified anymore (*). In each and any respect, water turbines are produced nowadays in the same way, as they have been 80 years ago.
So our first concern is, to simplify both the construction and production of conventional water turbines, making use of the general technical advancements of the last 80 years. A turbine of 100 kW should not cost 400.000 Euro, but rather 200.000, or maybe 100.000 Euro.
We would like to collaborate with interested companies for developing a new kind of low-cost water turbine for small heads (below 2 meter), and can provide a complete drawing of a small prototype turbine under non-disclosure agreement. Later on, water turbines with increased flow velocity will be constructed.
(*) we refer to turbines under low heads. For very large heads, the price of the turbine is small compared to the price of civil construction, for which reasons large overall savings are not possible.