Wind Power

1. 3 Responses to “What would create more power from wind or water energy? Multiple small generators or one large one?”

2. By Robbie S on Dec 2, 2009 | Reply

   Just think of which system will enable the most outside forces to impede on the overall output.

   In a theoretical world w/o wind drag, friction, etc, the two solutions should behave equally. However, with many generators, there is the rotational friction (as the motional part spins around and around), air resistance as the moving parts move, etc. These forces take away some of the overall output, so minimizing these forces will maximize output. Having one big generator is more efficient because a smaller percentage of it’s energy is lost to the world.

   Do you know what kinetic energy is? it is the equation used to describe the amount of energy a moving object has. it is:
   kinetic energy = 1/2mv^2
   where m = mass and v = velocity.

   It is difficult to do anything useful w/ generators w/o calculus but just know that the kinetic energy of the moving water (or wind) get’s directly converted into electrical energy when it cycles through the generator.

   By looking at that equation you can see that if the water (wind) moves faster, the kinetic energy increases, which means the generator output increases.

   It takes more energy to move bigger sized revolutions, so by increasing the size of a revolution it would only slow down.

   If you sped up or slowed down the revolutions (which would happen with greater velocity of water or wind), the kinetic energy would increase so the output would increase.

3. By monophoto on Dec 6, 2009 | Reply

   Its probably possible to produce the same amount of energy from water and wind. However, the individual unit sizes might be quite different.

   In the hydroelectric world, the two factors that determine the potential amount of power to be generated are the design of the turbine and head/flow of the water. The greater the head/flow, the more power that can be produced. It is not unusual to see individual units that are several hundred megawatts in rating in hydroelectric plants.

   Fundamentally, the same factors are present in the case of wind. However, wind tends to be limited in its availablity. Therefore, the issue becomes that the diameter of the turbine becomes the limiting factor in determining the rating that is possible. The largest wind turbines today are around 5-6MW, and it is unlikely that we will see anything much larger than perhaps 8-10MW in our lifetime.

4. By Ryan Z on Dec 6, 2009 | Reply

   I think the easiest way to explain this is to start at the beginning. Think of the flowing water (or air) as a momentum-carrying body that has kinetic energy that can be captured by your generators. The larger the area covered by your rotor (the blades of your wind or hydro generator), the more energy that can theoretically be produced. The swept area of the rotor is a circle - as you know from math, the area of a circle is pi multiplied by the radius squared. Therefore, the energy you can extract from generator increases proportionally to the square of the blade length (the radius). Therefore, it is generally much more efficient to have one large generator than it is to have multiple small ones. This is playing out in the wind industry today - 20 years ago the most cost-effective wind turbines were around 10-50 kW each, 10 years ago they were around 100-500 kW each, and today they are 1000-3000 kW each!

   The output of a generator is dependent on the amount of torque that is applied to it and the speed at which it rotates. The generator needs to be sized appropriately according to the size of the rotor - you could but a 3000 kW generator onto a 50 m rotor diameter but it wouldn’t be very efficient. a 500 kW generator would be better sized to a 50 m rotor, just as a 3000 kW generator is appropriate for a much larger 100 m rotor diameter.

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