<story><title>Why Wind Turbines Have Three Blades</title><url>http://www.cringely.com/2016/05/06/15262/</url></story><parent_chain><item><author>mapt</author><text>* I don&amp;#x27;t understand his explanation of starting torque.  You can jump-start that problem by other means in the alternator.  Torque and power should be decoupled anyway by blade pitch.&lt;p&gt;* There is such a huge difference between a 12m blade and a 60m blade that I don&amp;#x27;t see how the comparison is at all relevant.  We played with smaller turbines for &lt;i&gt;decades&lt;/i&gt; before we reached this sort of price efficiency.&lt;p&gt;* Betz&amp;#x27; law explicitly disavows picking a number of blades:  &amp;quot;Assumptions:  1. The rotor does not possess a hub and is ideal, with an infinite number of blades which have no drag. Any resulting drag would only lower this idealized value.  ...&amp;quot;&lt;p&gt;* Betz&amp;#x27; law is a three-dimensional consequence of convervation laws, not an observation about turbulent blade interactions.  &amp;quot;Consider that if all of the energy coming from wind movement through a turbine was extracted as useful energy the wind speed afterwards would drop to zero. If the wind stopped moving at the exit of the turbine, then no more fresh wind could get in - it would be blocked. In order to keep the wind moving through the turbine there has to be some wind movement, however small, on the other side with a wind speed greater than zero. Betz&amp;#x27; law shows that as air flows through a certain area, and when it slows from losing energy to extraction from a turbine, it must spread out to a wider area. As a result geometry limits any turbine efficiency to 59.3%.&amp;quot;&lt;p&gt;* We already have a good idea what a moderate redesign of the fundamentals of a wind turbine looks like;  It points downwind, it&amp;#x27;s huge like the existing turbines, and its two blades bend.  They just need to solve the tower strike problem. &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;401583&amp;#x2F;wind-power-for-pennies&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;401583&amp;#x2F;wind-power-for-pen...&lt;/a&gt;  &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;528581&amp;#x2F;two-bladed-wind-turbines-make-a-comeback&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;528581&amp;#x2F;two-bladed-wind-tu...&lt;/a&gt;</text></item></parent_chain><comment><author>drostie</author><text>Furthermore, this idea that nobody&amp;#x27;s studying the number-of-blades problem is bogus too. When I worked abroad as a research assistant in the Wind Energy Project Group at the TU Delft (biggest tech university in the Netherlands), one of the researchers showed me a very interesting wind turbine that had a massive, elegantly curved blade on the one side and a big blob on the other. He explained, &amp;quot;We&amp;#x27;ve been doing some simulations on these one-blade designs, even though they look goofy. This blob is just a counterweight, it is very cheap to produce because you don&amp;#x27;t need any advanced materials to use it. So the question is, if you had three times the budget to spend on just one blade, could you make it so good that it would outclass the three-blade model completely?&amp;quot;&lt;p&gt;In fact I asked why he wasn&amp;#x27;t going with 5 or 7 or 9 blades (he explained that even numbers tend to be Bad News) and he explained that the big problem was, as you increase the number of blades, the proportion of the rotor disk that consists of blade gets higher, which means the force on the  tower component gets larger -- it goes something like the third power of wind-speed. Every few years or so, hurricane-force winds batter parts of Europe, and therefore there is a massively important design requirement that the wind turbine not completely be obliterated during these violent storms. An airplane with a funky propeller can of course be stored indoors when this happens; a turbine would require maintenance technicians to disassemble each one the day that the high-wind forecast was received.&lt;p&gt;Googling some of these related issues brings me to the page:&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;mstudioblackboard.tudelft.nl&amp;#x2F;duwind&amp;#x2F;Wind%20energy%20online%20reader&amp;#x2F;Static_pages&amp;#x2F;blades_number.htm&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;mstudioblackboard.tudelft.nl&amp;#x2F;duwind&amp;#x2F;Wind%20energy%20o...&lt;/a&gt;&lt;p&gt;However I cannot say with great certainty whether this is the same person that I heard these things from, or just a peer in the same field with the same general conclusions.</text></comment>
<story><title>Why Wind Turbines Have Three Blades</title><url>http://www.cringely.com/2016/05/06/15262/</url></story><parent_chain><item><author>mapt</author><text>* I don&amp;#x27;t understand his explanation of starting torque.  You can jump-start that problem by other means in the alternator.  Torque and power should be decoupled anyway by blade pitch.&lt;p&gt;* There is such a huge difference between a 12m blade and a 60m blade that I don&amp;#x27;t see how the comparison is at all relevant.  We played with smaller turbines for &lt;i&gt;decades&lt;/i&gt; before we reached this sort of price efficiency.&lt;p&gt;* Betz&amp;#x27; law explicitly disavows picking a number of blades:  &amp;quot;Assumptions:  1. The rotor does not possess a hub and is ideal, with an infinite number of blades which have no drag. Any resulting drag would only lower this idealized value.  ...&amp;quot;&lt;p&gt;* Betz&amp;#x27; law is a three-dimensional consequence of convervation laws, not an observation about turbulent blade interactions.  &amp;quot;Consider that if all of the energy coming from wind movement through a turbine was extracted as useful energy the wind speed afterwards would drop to zero. If the wind stopped moving at the exit of the turbine, then no more fresh wind could get in - it would be blocked. In order to keep the wind moving through the turbine there has to be some wind movement, however small, on the other side with a wind speed greater than zero. Betz&amp;#x27; law shows that as air flows through a certain area, and when it slows from losing energy to extraction from a turbine, it must spread out to a wider area. As a result geometry limits any turbine efficiency to 59.3%.&amp;quot;&lt;p&gt;* We already have a good idea what a moderate redesign of the fundamentals of a wind turbine looks like;  It points downwind, it&amp;#x27;s huge like the existing turbines, and its two blades bend.  They just need to solve the tower strike problem. &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;401583&amp;#x2F;wind-power-for-pennies&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;401583&amp;#x2F;wind-power-for-pen...&lt;/a&gt;  &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;528581&amp;#x2F;two-bladed-wind-turbines-make-a-comeback&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.technologyreview.com&amp;#x2F;s&amp;#x2F;528581&amp;#x2F;two-bladed-wind-tu...&lt;/a&gt;</text></item></parent_chain><comment><author>Pxtl</author><text>&amp;gt; They just need to solve the tower strike problem.&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;c2.com&amp;#x2F;cgi&amp;#x2F;wiki?JustIsaDangerousWord&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;c2.com&amp;#x2F;cgi&amp;#x2F;wiki?JustIsaDangerousWord&lt;/a&gt;</text></comment>