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Discussion in 'General Electronics Discussion' started by kamalahmad, Sep 22, 2014.

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  1. kamalahmad

    kamalahmad

    8
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    Jun 3, 2013
    My project : WIND TURBINE
    My thought : I want to remove batteries i.e i will give direct supply from turbine to home appliances.

    I have googled about it. but i did not see any turbine like this.

    problem ; in Ac , the problem is frequency mainly, bcz when ever the wind varies the frequency will vary.
    but if I use a turbine which gives me direct current and then I use a DAC(digital to analog convertor) then i can get the desired frequency . what do you think ? is it good?

    another thing is that, how many watts is required for a home .
    let suppose a home with a refregerator, 3 fans, 5 incandecent lights, a laptop charger and mobile chargers.
    how much watts needed then?
     
  2. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Probably best to ditch this idea.
    Wind speed will vary like you have said. This does not merely change the frequency, it will also change the power output.
    Additionally, when a high demand is placed on an electric generator, the force required to turn it increases. This will further slow down the wind turbine.

    Use a battery in the middle as a 'buffer' to compensate. It will store excess energy when the demand is not there, and provide energy when the demand is more than the turbine can handle in the current weather.

    Look on your products to determine how many watts they draw, or how many Amps they draw. Voltage is important too. Are you using a low voltage system, or are you generating 110, or 220V?

    Are you talking about a large stand-up fridge? The peak power required when the compressor is running could be quite high...
     
  3. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    Hey kamalahmad!

    The biggest problem with wind turbines is that there are very few habitable places in the world that actually have enough prevailing wind to make a wind turbine a viable investment... Large Scale Commercial wind turbines do typically produce AC power that is synchronous with the grid they are designed to supply; however, this is NOT something that can be easily scaled down to a consumer sized wind turbine, so I will omit a discussion about HOW this is achieved....I will start with available power in the wind:

    Code:
    The theoretically available power in the wind can be expressed as
    
    P = 1/2 ρ A v3  (1)
    
    where
    
    P = power (W)
    
    ρ = density of air (kg/m3)
    
    A = area wind passing through perpendicular to the wind (m2)
    
    v = wind velocity (m/s)
    
    
    NOT TO BE CONFUSED WITH:

    Code:
    Actual available Power
    which can be expressed as
    
    Pa = 1/2 ξ ρ A v3  (2)
    
    where
    
    ξ = efficiency of the windmill (in general less than 0.4, or 40%)
    
    
    PLEASE NOTE That both the THEORETICAL AND ACTUAL available power are functions of the Velocity of the wind CUBED!

    FURTHERMORE PLEASE NOTE: Economically Viable Wind Turbines need an absolute minimum of 9m/s (~20mph) wind speed. This is NOT an OPINION, this is a mathematical reality. I don't care what various wind turbine MFGs CLAIM about performance @ lower wind speeds, the mathematical reality is that at below 9m/s there simply is not enough available power to justify the materials required to build the turbine.

    SOOOO. the first step is an assessment of the site. First verify that there are no restrictions or codes expressly forbidding a wind turbine installation, or if there are restrictions or codes, find out exactly what they are. Next you need to determine what the prevailing wind speeds are. While national weather service information can be used as a general suitability guide, typically a two-year site study with anemometers placed at various elevations and the data logged 24/7 is considered sufficient due-diligence. Once the data is collected an objective analysis will help determine the most cost efficient design and elevation that codes and regulations will allow.

    Having said all of that, a much more typical "DIY" approach is just to throw up a wind turbine and "hope for the best"....rarely are these installations cost effective.

    As to "How Much Power Do you Need".....that really shouldn't be a "question", that should be something that you KNOW long before you start looking at wind turbines....regardless of how much "peak" power you decide you need you need to establish "how important" the uninterrupted power from the wind turbine is. If your site evaluation shows that 70% of the time the wind speed is 20m/s or greater 20% of the time the wind speed is 10m/s to 20m/s and 10% of the time the wind speed is < 10m/s AND you have alternative sources of power then I would think you would be best off sizing your turbine so it met 90% to 100% of your power requirements when the wind speed was 20m/s or more. If the wind turbine is to be your ONLY source of power AND it is critical that it not only supply your real-time demand but it also "store energy" for use when the wind is less than 20m/s then I would size it so that it would supply 150% of your demand @ 10m/s....

    While it MIGHT seem like a "no brainer" to just go with, "the larger turbine", this will have a huge negative impact on the economic viability of the proposed wind turbine! Assuming an optimistic efficiency of 30% and average usage of 4.8kWh/day.....To supply 100% of the requisite power @ 20m/s would require a turbine with a swept area of:

    Code:
    Po = Power Output = 4.8kWh/day --> 200W
    Pa = Po
    200W = 1/2 * (0.30) * 1.127 * A * 20^3 ==> Area = 0.14789m^2 ==> ~43.4cm Diameter
    
    To supply 150% of your demand @ 10m/s would require a turbine with a swept area of:
    Code:
    Po = (4.8kWh * 1.5)/day --> 300W
    300W = 1/2 * (0.30) * 1.127 * A * 10^3 ==> Area = 1971m^2 ==> 50m Diameter
    
    Obviously a wind turbine with a blade diameter of of 43.4cm is going to cost a FRACTION of what a wind turbine with a blade diameter of 50m is going to cost. THIS is the reason a two year site assessment is considered an essential part of the evaluation process...wind speed cubed makes a HUGE difference in the potential economic viability of a wind turbine.

    To put things in perspective, if grid power were available @ $0.20/kWh then the cost of power per day would be ~ $1.00/day or $365 per year.....Even the installation of a 1/2M diameter wind turbine is going to cost over $1000 suggesting that a "best case" break-even point would be roughly three years, and this "break-even-point" makes a laundry list of optimistic assumptions.....A 50M Diameter wind turbine could NEVER reach a break-even point unless it were placed in a highly favorable location.


    Soooo, Back to the first step: Site Assessment. If you cannot 100% verify wind speed > 10m/s the VAST MAJORITY of the time then there is no economically viable solution.

    If you believe your site location to be one of the very few habitable places on earth where the prevailing wind speed > 10m/s then I will be HAPPY to help you assess the economic viability....if not then likely the best thing to do if you still feel the need for a wind turbine is order one and put it where ever you see fit; how you hook it up and what you do with the power it produces are of little consequence, lol.

    There are some things you can do with wind mills that make good economic sense in remote locations...even ones with less than ideal conditions for producing electricity...For instance replacing an electric or gas well pump with a wind-driven well pump and a water tower or elevated cistern can make great economic sense.....In areas w/o available grid service wind turbines can be used to produce electricity for charging batteries etc and can compare favorably to fuel driven generators in fiscal viability....In these special cases you are no longer comparing the cost per kWh with the cost of grid supplied power....If you are 600 miles from a fuel station then the cost of fuel generated electricity could easily exceed $10/kWh in which case the production of even 100 kWh per year could pay for itself very quickly....

    FWIW nearly All electricity produced by mechanical means is AC, and there is no "useful" conversion of mechanical energy directly to DC.....An example of DC generated by mechanical means would be the production of "static electricity" ie a potential difference relative to ground that accumulates over some period of time....but to date nothing particularly useful has been found for this type of electricity. Some might argue that the early "dynamos" were "DC GENERATORS", but in reality these machines were simply AC generators with synchronous rectifications achieved by mechanical commutation. The most efficient conversion of mechanical energy to AC electricity is a poly-phase alternator, typically actualized as a three-phase sinusoidal wave form. So to answer you question about how one might "match the grid frequency" the answer is typically with an "Inverter" designed specifically to convert a DC voltage to an AC voltage and in some cases synchronize it with the grid.....The flow diagram would go something like this: 1) Wind Blows--> Turbine Produces 3 phase AC Output @ some frequency 2) The AC output is routed to an inverter or charge controller where in either case it is rectified to DC. 3) In the case of an Inverter, the rectified AC is fed into the inverter and converted back into an AC voltage.....Each time energy is converted some percentage of the enrgy becomes "waste heat"....In several of the conversions the percentage can be quite large.....for instance the conversion from the AC generated by the turbine to DC is typically the Voltage Drop of the Diodes used multiplied by the current flowing through them...so if the Wind Turbine output 11.5V @ 10 Amps = 115Watts, then if it is rectified with diodes that have a 1.5V forward voltage then 1.5Vf * 10A = 15W is LOST to heat converting from AC to DC...if the inverter used to convert the DC back ot AC is 80% efficient then of the 100Ws still available @ the inverter's input, only 80Ws will be available @ the inverter's output, so. not counting other losses, in just these two conversions our 115W output has been lowered to 80W of "useful" energy....If you could find a way to directly use the output of the turbine (say to power "resistive heating elements" designed to work with ~ the nominal voltage/current of the turbine) then you would get ~30% more "useful output" than you might "converting the turbine output to a "standard AC wave form" and then powering resistive heating elements from the **twice** converted power.....The point here being, if you carefully analyze your power requirements you can potentially get far higher efficiency from your source than you can "converting it to a standard AC wave form and then using it..." For instance if you knew you had numerous devices that required a 12V input to "charge", you might be much better off charging those devices with "special chargers" designed to directly use the turbine's output rather than "plugging the chargers into a wall socket powered by an inverter using the wind turbine's output." In the previous example where we had 115W and saw that it was reduced to 80W of output from the inverter, if we had 5 "wall-wort" chargers that each output 12Vdc and had an average efficiency of 70% and an "Average" charging current of 1A each then the demand on the Inverter would be 12W/0.7 = 17.14W input to each charger * 5 Chargers = 85.71W......5.71W more than is available! BUT if we took the time to design and build equivalent chargers for the devices that were 90% Efficient and powered directly from the Turbine's output these chargers would only consume 12W/.9 = 13.33W ==> 13.33W * 5 = 66.67W so we would still charge all 5 devices but this way have ~48W available @ the inverter's rectifier input demonstrating HOW IMPORTANT it is to carefully examine how the turbine's output is utilized....

    In summary, attempting to "create grid compatible energy" from wind/solar is generally NOT a fiscally viable approach to individual production and utilization of renewable energy sources....a far better approach is to attempt to efficiently power devices directly from the renewable energy source thus eliminating "some grid demand" without attempting to produce grid compatible power.....

    All I have time for....lol.

    Fish
     
    kamalahmad, KrisBlueNZ and Gryd3 like this.
  4. kamalahmad

    kamalahmad

    8
    0
    Jun 3, 2013
    i thought about this varying wind and i thought about i will use a PLC which will switch on , when ever the power goes down to the needs. regardless of the wind speed because the back circuitry which the plc turn on will give power to wind turbine to turn fast and as the result desired power can be achieved.
    the wind is blowing and the back circuitry will only give the required power to generate the power needed for appliance.

    how about this?
     
  5. davenn

    davenn Moderator

    13,617
    1,881
    Sep 5, 2009
    kamalahmad

    did you read any of fish4fun's post ... I know it was a long one, but it has lots of valuable and important information that you need to carefully consider

    You also didn't answer any of the questions asked of you


    cheers
    Dave
     
  6. kamalahmad

    kamalahmad

    8
    0
    Jun 3, 2013
    i live in Karachi, Pakistan. Wind is not a problem here.
    I have read fish4fun's post. i fully agree with it.
    But I am not attempting to do what has already done. I have come up with a new idea. that is , I dont really depend upon the wind. it means that what i have replied to GRYD3. that I am planning to control the wind turbine . whenever i need more watts that I can turn the speed up of the wind turbine.

    Fish4fun has showed me what the wind turbine available these days will act on the available wind .
    though I really appreciate the reply of fish4fun and thanks to him that he spent alot of time writing that post.

    But my idea is completely different from these wind turbines.

    I want to remove the batteries and I want to control the wind turbine that means i don't rely on the wind.
     
    Last edited: Sep 24, 2014
  7. davenn

    davenn Moderator

    13,617
    1,881
    Sep 5, 2009
    That doesn't make too much sense
    You will need to explain more clearly what you want to achieve :)

    Dave
     
  8. kamalahmad

    kamalahmad

    8
    0
    Jun 3, 2013
    fish4fun

    thanks for your detailed post. I appreciate your work.
    I have learnt a lot of things from your post.
    you have given me things that I must know.
     
  9. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    Really?

    I think you might have missed this bit:

    Please understand that a site with an average wind speed that varies from 5mph to 13mph is NOT an economically viable site under NORMAL considerations. That being said, if grid power is 1) unavailable 2) unreliable 3) VERY expensive then the site **might** be considered suitable based on these mitigating factors. Following is a spreadsheet showing the Available Energy in a ~1m diameter wind turbine.....The calculated "Available Power" has the 59% betz limit ( http://en.wikipedia.org/wiki/Betz's_law ) incorporated, the "CP" = Coefficient of Power and is a "de-rating factor" to account for the deviation between "Theoretical Limit" and "Actual Extraction", that is: it is a measure of the blade/bearing efficiency.....NONE of these calculations include the efficiency of converting mechanical energy to electricity....typically an additional coefficient between 0.20 and 0.60.


    upload_2014-9-24_5-57-50.png


    So...if we assume the annual "average" wind speed is ~4.5m/s (10mph) then you could expect an "annual average" mechanical extraction rate of ~27W per m^2 of swept area. Converting 27W of mechanical energy to electricity might provide 16W of output from your turbine's alternator if your alternator is designed and built to maximize the efficiency at these very low nominal conditions. If we assume that the local cost of labor is negligible and that there are no codes/regulations/licenses/taxes to contend with and that engineering will be DIY AND that the majority of the construction materials will be locally obtained and "re-purposed" then it **MIGHT** be possible to build a turbine in the 3m^2 to 10m^2 swept area range for as little as $100.m^2. So...16W/m^2 * 24 * 365 => 140kWh/Year (per m^2). The cost per kWh for 1 year would be ~$2.15/kWh. Assuming the turbine had zero maintenance costs and had a useful lifespan of 10 years then the cost per kWh spread over 10 years would be $0.22/kWh....honestly a relatively reasonable cost, but ONLY because of the mitigating factors involving both the cost of the build AND the mitigating factors surrounding other available sources of power.

    But...to put things in perspective, a gallon of gasoline or diesel fuel has roughly 9.2kWh/liter of "available energy".....small-scale conversion (ie a small gas/diesel generator) can convert this to electricity at the rate of ~1/kWh/liter....So the "gasoline equivalent" would be roughly 140l/year/m^2 of swept area, or 0.38liter/day/m^2 of swept area or 16ml/hr/m^2 of swept area. Over the 10 year life of the turbine you might save the "gas equivalent" of 1400 liters (~380 US gallons) of gas per m^2 of swept area.....

    Anyway, if you believe that this is a viable project then I will be happy to help you with your design, but from my perspective this is a lot of work for a fairly trivial amount of energy.....but if there are no other viable energy sources then it may well be worth it....(Though it would take several m^2 of swept area at these wind speeds just to power laptop a few hours a day....)

    Fish
     
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