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Forum Index : Windmills : Total possible watts? Why so low?
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arpolis Newbie  Joined: 04/08/2010 Location: United StatesPosts: 26 |
Hello to every one! I am trying to learn a lot befor I get into any harry larger scale wind turbins but I find all this so exciting and can't wait to go full scale. I was looking arround and found a site with a calculator that figures what the total amount of possible watts are available from the wind. "http://eduhosting.org/windpics/wgwatts.html#doit" I looked up my areas average wind speed and all year round it is close to 10mph. I figured I would use 3.5ft blades. With that in mind I put in the #s and total watts are 60.831 and Amps are 1.26725 with a 48V windmill. Does that sound right? No matter the altenator used or cunstructed could affect this? From the same site to generate a 1kw wind turbin in my area, I would need a blade diameter of 25 - 30ft across. I am not turned off of wind but it seems that wind power will barely put a dent in my bill unless I go huge!  Any ideas?Will it work? Well lick your fingers and touch the two leeds. PZZZZZZZT |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi arpolis Afraid so, you need to go big to get any reasonable power from wind. See this thread http://www.thebackshed.com/windmill/forum1/forum_posts.asp?T ID=2860&PN=1 The small roof top wind turbines you see advertised wont live up to expectations, and a lot of people have been bitten. Fact is you need to go big to make significant power from the wind. But once you get up over 3 meters in diameter, you can start to make good power and it becomes a financially worth while exercise. It doesn't matter how efficient the turbine is, or the alternator, there is only so much power that can be extracted from a column of wind. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
arpolis While there are mathematical formulas to determine the "potential" power in a stream of wind (Power in Watts = Air Density / 2 X Swept Area X Velocity^3 -- Thanks, Gizmo), a lot of it comes right down to design. Think of it as if you were surfing and get caught in a rip current, taking you out to sea. You can paddle straight black to shore until your arms fall off and still wind up two miles off shore. On the other hand, you can realize what's up and paddle somewhat leisurely across the current and be out of it in no time at all with very little extra effort if any. My point here is this: If you know your wind speed, you can build a set of blades and an alternator that will match your needs. Granted, if you want to light the entire city, you'll have to jump through some pretty large hoops, but still, it is "possible". My advice to you would be to read through several topics covered here on the forum and when you have digested some of what's here, then decide on what your "real" intentions are and go for it. A windmill with a 7-foot diameter prop as you have eluded to here is more than capable of producing way more than 1.26 amps at 48 volts. While it is true that the blades and the alternator must be matched for optimum performance, 60 watts is nothing. I think I'd stay away from that power calculator you're using and stick to what's presented here on the 4m. Everyone here is in somewhat the same boat, though some are true "experts" (I not being one, by the way), everyone is trying to turn the afternoon breeze into useable electric (mostly) power. Here is another fellow just starting out; maybe follow his lead, eh? Edit: Added link . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| arpolis Newbie Joined: 04/08/2010 Location: United StatesPosts: 26 |
TY all for the comments. Now on the equation for the watts I guess I am a bit lost. maybee its in some conversion or somthin. You have "(Power in Watts = Air Density / 2 X Swept Area X Velocity^3 -- Thanks, Gizmo)" SO I calculated 1.23kg * .5 * "Swept area" * Wind Velocity ^3. "Swept area" I just calculated a circles area. 3.141592*3.5ft^2 = 38.484502 Velocity was 10MPH Cubed which is 1000MPH So we have 1.23*.5*38.484502*1000=23667.96873 ??????? I think I missed somthing some where lol. Also both links in the thread dont work for me. says I am not connected to internets but I can brows normally. I even copied and pasted the first link and still same problem. Weird! Will it work? Well lick your fingers and touch the two leeds. PZZZZZZZT |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi arpolis All figures in metric. 3.5feet is 1.066m. Your area would be 3.568m2. 10MPH is 16kmh. Convert that to meters per second is 16khm * 1000 / 60 / 60 = 4.44ms So, 1.23 * 0.5 * 3.568 * 4.44^3 = 192W Knock off 60% for turbine efficiency, we get 76 watts shaft power. Knock off 30% alternator efficiency, we get about 53 watts. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Actually looking at the figures in your first post, its pretty close to what the calculator said. Increase the diameter and or wind speed and see what the figures do, the power goes through the roof. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Hmmm . . . My apologies; apparently your calculator is okay and I was mistaken. After posting I got to thinking about it and was sorry I'd said 60 watts was no big deal. Unfortunately, the "edit" feature magically disappeared and I was stuck with my foot stuck squarely in my mouth (not the first time). I'll try to be more careful in the future. At any rate, I'd suggest you do a little studying and then build something. Even if what you build doesn't work right off the bat exactly as you'd planned, you'll gain some valuable building experience and learn a lot along the way. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| arpolis Newbie Joined: 04/08/2010 Location: United StatesPosts: 26 |
Wow TYVM Gizmo. I knew it was a matter of metric/standard conversions. I went to weatherunderground.com and pulled some data for the last 12 months and came up with this. For the 3.5ft blades, each month has a 5 mile per hour average and a peak average of 25. If I do some math right I have an average hourly power input into the grid "assuming turbin produces for all wind speeds" 6.81 watts and the average gust of wind getting up to 857.43 watts at a time. Also looks that I need to figure how to properly furl for wind past 25MPH because last January there was one recorded wind gust of 60MPH so I can see the disaster waiting there. Thanks again every one. Another thing to spend some spare time on. 
Oh wanted to add that the calculator read the 5MPH speed at 7.67 watts and the 25MPH wind at 952.147 watts so I think I will stick with the pen and paper because it gives me a little less and I am sure is accurate so if I get more I will be surprized. Will it work? Well lick your fingers and touch the two leeds. PZZZZZZZT |
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