Wind power from low speed

The maximum power that can be extracted from the wind is proportional to the cube of the wind speed. So, to use your example speeds of 5 and 6.9 mph wind speed - even though it's a small difference, a turbine operating at the higher speed delivers 2.5X the power. You can also increase the power by increasing the swept area of the blade, but that's only a linear relationship.

Below some minimum wind speed, it just isn't economical to build a turbine because the energy available to be harvested is too small.

There's a good discussion of the principles of wind power generation on the British Wind Energy Association website

Sorry, I meant m/s not mph, though it doesn't change anything.

I think that you missed my point. Using your reasoning then we should use the next level of wind above the 6.9 because it provides more power. This is not what I am suggesting or asking. I want to know if anyone is working on developing a blade or a multiable bladed system that will capture the power from the lower speed winds. Remember the old windmills had lots of blades so they could capture the wind and turn it into work. Not many of then exceded 10 or 15 meters high and the winds probably didn't reach the 5 m/s mark. There are a lot more of the lower wind areas available and lots of them provide these winds for a greater percentage of the year.

>I think you missed my point

I don't think so, although I've been known to be wrong before :-)

>I want to know if anyone is working on developing a blade or multiable bladed system that will capture the power from lower speed winds.

My point in the previous post was:
Below some minimum wind speed, it just isn't economical to build a turbine because the energy available to be harvested is too small.

The only real way to increase the power significantly is by increasing the swept area, but that means larger structures and higher cost. It just isn't worth it for the amount of energy you get back.

Let me explain it in a different way.
First I agree with you that the swept area at 6.9 m/s gives you 2.5 times more power than the 5 m/s. But, "The power efficiency of the rotor is the fraction of the total power available which the blades are able to convert. The theoretical maximum is 0.59. This is known as the Betz limit."

Next lets assume that our wind generators have equal operating swept areas. Yours has 250 units of power available and mine only has 100. Your system has three blades and mine will have six, and if you understand Betz limit then using rounded numbers yours will extract 30% of the available power and mine will extract 60%. (This is because the 6 blade system is the point where, if there were more blades they would begin to interfere with the efficiency of the others and the efficiency actually goes down not up, unless it is ducted.) Your unit will provide 75 units of power per hour of operation and mine will provide 60 units per hour.

Your availability is some where around 50% of the time so out of the 8,760 hrs in a year you only get 4,380 hours of power or 328,500 units of power. My availability is closer to the 80% so I get 7,008 hours of power or 420,480 units of power. That is 28% more power than you.

From what I have read about the industry, they claim that they can pay for each tower in three years of operation. Using this information, my tower can cost 28% more than yours and at the end of the three years I will then start to have a 28% greater profit than you. To take this a little further I will have 10 times as many sites available to use as you, which makes my potential profit 280% more than yours.

Increasing the swept area is not the only way to increase the power; we can increase blade efficiency, increase the number of blades or maybe even change the design to a ducted system. So I cannot agree with your economics of the best way is to go to the next higher classification of wind.

Again I will ask if anyone is working on developing a blade or multiple bladed system that will capture the power from lower speed winds.

Why am I persistent on this? Well I live in Peru and I know the area that is on the World Map previously mentioned. I know exactly where the weather station is located and a lot about missing information. I don't have the financial capability at this time to set up the necessary towers to collect the more accurate information requires to show that it is very possibly the next higher wind area classification, which would make it more lucrative to investors. I need to start with the lower wind system development and if I can help to start promoting this or encouraging its entrance into the wind farm community. Then I will have a place to test it, and possibly have made a difference for the People of Peru and all of those other 5 m/s sites in the world.

Dear Friend, As one who works in this R&D area, along the studies about efficiencies of the wind-blades systems I am working on the generators output efficiencies improvements and I think I can help you. But to answer imediately at your question I will copy below part of a website which in may oppinion will make "light" in your peoples homes. "Despite the excellent testing results, the strongest qualities of the (vertical shaft, n.r.)turbine were discovered in the actual production usage. The strongest advantage of Windside lies in its ability to take advantage of even the lowest wind speeds. The electricity production of Windside begins even with the wind speeds as low as 2-3 m/s, and the bigger the turbine is, the lower wind speed it requires to start. According to measured results, the 3 m/s winds blew during 100 days per year in inland areas. The propeller models based on the traditional aeroplane engineering cannot take advantage of these light winds, usually their production begins at wind speeds of 4-5 m/s, from moving wind. The wind direction is not a significant factor for Windside, either, since the wind catches the spiral-shaped vanes always from the right angle. No automatic, easily braking turning mechanisms will be needed" So, take a look on www.windside.com and tell me if is not you are looking for. Feel free and contact me for any further questions. Regards, Dumitru