Fake news !

[topspeed]

 

I started with somewhat loaded term, but forgive me....my matter is urgent !

Here you can see the formula that defines how to count the out put of any wind turbine when you know the right figures: https://thundersaidenergy.com/downloads/wind-power-impacts-of-larger-turbines/

I have come a cross few wind turbines that are sold as 5 KW and 7 KW...using the equation in the link I counted that in 10 m/s wind the former (5 KW) is able to produce 375 watts.....and latter 7 KW only 100 watts from the wind.


How is this even possible ?

5 KW is sold for people in the archipelago here (off grid) and other was pointed out to me by a dude who said where do I need your contraption as I can buy 7 KW system at 1250 USD. I noted him clarifying that most it can do is 100 watts...it was like abig blender...400 x 800 mm sized.

Then people get really angry as they think I am lying and pretend know things better than the professionals !

[Adriaan Kragten]

The electrical power of a wind turbine can be calculated with formula 4.2 of my public report KD 35. So even if someone has no aerodynamic knowledge, he can check if the power as specified by a supplier is realistic by putting realistic values of the Cp and the efficiency of generator and transmission in this formula. A big problem is that most suppliers only mention the peak power at a very high wind speed. This is especially the case for wind turbines which have no safety system which limits the power, the rotational speed and the thrust at high wind speeds. So this extremely high peak power has not only the disadvantage that it is supplied only for some hours a year but also that a wind turbine without a proper safety system can be very dangerous. A very high peak power also has as disadvantage that all electric components behind the generator like the rectifier, the cables, the voltage controller and the dumpload must be very large other wise they will be blown during a strong wind gust.

What you need to judge the usefulness of a wind turbine in a certain wind regime, is the Pel-V curve. This curve gives the electrical power as a function of the wind speed. This curve starts at the so called cut-in wind speed. The rotor starts rotating at the starting wind speed when the starting torque of the rotor is larger than the cogging torque of the generator. If the generator has a large peak on the cogging torque, the starting wind speed can be much higher than the cut-in wind speed resulting in hysteresis in the Pel-V curve. So if the cut-in wind speed is 3 m/s and if the starting wind speed is 5 m/s, you only get power at 4 m/s if the wind speed has been higher than 5 m/s in the recent past. This is another reason why people can be very disappointed about the power output of their wind turbine if they live in a region with rather low wind speeds.

All VIRYA wind turbines which I have designed have an effective safety system and for all public designs I give a Pel-V curve. These curves are given in folders which can be found at the menu VIRYA-folders at my website: www.kdwindturbines.nl. So if you want to buy a commercial wind turbine, be sure that the supplier supplies a Pel-V curve. If this curve isn't given, you will be disappointed.

[topspeed]

Check these out: Tesup Atlas 7 KW

https://www.tesup.fi/product-page/hera-wind-pro-tuuliturbiini-taloille?gclid=Cj0KCQjwho-lBhC_ARIsAMpgModeDiGPUxuyiFpFLS8A8hJYJwpZa4v0BVpJR810ONBokYVu4fP8KkEaAm5REALw_wcB

Adrian is right...this one says theorethical maximum 5 KW. It is only 2 x 2,5 meters in size...and savonius in principal.

https://verkkokauppa.saaristotekniikka.com/product/508/5-kw-pystytuulivoimala-silentmill

But if it only produces 375 watts at 10 m/s...what is it good for ?

[Adriaan Kragten]

A wind turbine without a safety system can produce a very high mechanical power at very high wind speeds. Formula 4.1 out of KD 35 shows that the mechanical power P increases with the cube of the wind speed. Formula 4.2 shows that the electrical power Pel also increases with the cube of the wind speed. However, this is only true if the Cp is maintained at the maximum value and so if the rotor is loaded strong enough. Formula 4.3 shows that the torque Q goes up with the square of the wind speed if the torque coefficient Cq is maintained at its optimum value. So this means that the torque level at V = 20 m/s is a factor four higher than at V = 10 m/s if Cq is maintained at its optimum value. So a very high maximum electrical power at very high wind speeds is only possible if the generator has a very high maximum torque level.

A PM-generator has a certain maximum torque level depending on the size and the construction. If this maximum torque level is reached at V = 10 m/s it will be the same for V = 20 m/s. So such a generator can't load the rotor strong enough at V = 20 m/s to make that the Cp is maximal. This means that at V = 20 m/s, the rotor will run at a much higher lambda than at V = 10 m/s and the Cp of the rotor will therefore be much lower than the maximum value. So the electrical power won't increase with the cube of the wind speed. So if the supplier of a small wind turbine specifies an extremly high maximum electrical power, often this high electrical power will not be supplied, even not at very high wind speeds because the maximum torque level of the generator is much to low. Generators with a high maximum torque level are big and therefore expensive. The generator will already be rather big if the maximum torque level is reached at V = 10 m/s. But even if the generator is that big that it can supply a very high electrical power at high rotational speeds, the heat losses will then also be very high which may result in burning of the winding. So limitation of the maximum rotational speed by a safety system is not only necessary to protect the rotor but also to protect the generator.

[topspeed]

A wind turbine without a safety system can produce a very high mechanical power at very high wind speeds. Formula 4.1 out of KD 35 shows that the mechanical power P increases with the cube of the wind speed. Formula 4.2 shows that the electrical power Pel also increases with the cube of the wind speed. However, this is only true if the Cp is maintained at the maximum value and so if the rotor is loaded strong enough. Formula 4.3 shows that the torque Q goes up with the square of the wind speed if the torque coefficient Cq is maintained at its optimum value. So this means that the torque level at V = 20 m/s is a factor four higher than at V = 10 m/s if Cq is maintained at its optimum value. So a very high maximum electrical power at very high wind speeds is only possible if the generator has a very high maximum torque level.

A PM-generator has a certain maximum torque level depending on the size and the construction. If this maximum torque level is reached at V = 10 m/s it will be the same for V = 20 m/s. So such a generator can't load the rotor strong enough at V = 20 m/s to make that the Cp is maximal. This means that at V = 20 m/s, the rotor will run at a much higher lambda than at V = 10 m/s and the Cp of the rotor will therefore be much lower than the maximum value. So the electrical power won't increase with the cube of the wind speed. So if the supplier of a small wind turbine specifies an extremly high maximum electrical power, often this high electrical power will not be supplied, even not at very high wind speeds because the maximum torque level of the generator is much to low. Generators with a high maximum torque level are big and therefore expensive. The generator will already be rather big if the maximum torque level is reached at V = 10 m/s. But even if the generator is that big that it can supply a very high electrical power at high rotational speeds, the heat losses will then also be very high which may result in burning of the winding. So limitation of the maximum rotational speed by a safety system is not only necessary to protect the rotor but also to protect the generator.

I took this topic up with one airplane mechanic yesterday.

He mentioned he had a 1,8 dia HAWT type chinese wind turbine on 6 meter pole on the coast here....and he claimed it used more energy than it produced.... battery was always empty.

I bet this has happened to many here.

5-10 KW wind turbine indeed is a big apparatus...at least 5 m wing and 4-5 m diameter on a VAWT. No one still should be selling a milk shake blender sized savonius systems as 5-7 KW systems...it is ridicilous...and fraudulent.

[electrondady1]

wow ! a toy windmill for 1600 bucks

[topspeed]

wow ! a toy windmill for 1600 bucks

Battery was supposed to charged by the windmill but the control unit used more than the windmill generated.

[Adriaan Kragten]

wow ! a toy windmill for 1600 bucks

Battery was supposed to charged by the windmill but the control unit used more than the windmill generated.

This is strange. Where is the wasted power used for? A battery charge controller for a wind turbine normally contains a voltage controller and a dump load. If this system is well designed, almost no power is used by the voltage controller if the wind turbine is producing no power. The dump load is only activated if the charging voltage is higher than the maximum charging voltage of the battery. It might be that the voltage at which the dump load is activated is adjusted too low for the nominal battery voltage or that the system contains an analogue volt meter which is always dissipating some power.

A free manual of a 27.6 V, 200 W battery charge controller is given at my website: www.kdwindturbines.nl at the bottom of the menu KD-reports. The wire diagram of the voltage controller is given in figure 1 of the manual. The battery voltage is available over the resistors R1, P1 and R2 which are connected in series. The total resistance is 26700 Ohm. So the current at a battery voltage of 24 V is 24 / 26700 = 0.0009 A. So the power loss is
24 * 0.0009 = 0.0216 W. It will take a very long time to empty a 24 V battery with this power.

The problem of heat generation in the generator at high rpm is especially large for battery charging. The battery charge controller makes that the voltage is kept at a constant value. The generator efficiency decreases strongly at increasing rotational speed if the voltage is kept constant (see measurements given in report KD 78). This makes that heat generated in the winding increases strongly at increasing rpm. So if the wind turbine has a low cut-in wind speed, the voltage at high rpm will be very much lower than the unloaded voltage. Wind turbines which are grid connected by an inverter are much better on this point because the inverter accepts a low voltage at low rpm and a high voltage at high rpm and this makes that the generator efficiency is also high at high rpm.

[topspeed]

wow ! a toy windmill for 1600 bucks

Battery was supposed to charged by the windmill but the control unit used more than the windmill generated.

This is strange. Where is the wasted power used for? A battery charge controller for a wind turbine normally contains a voltage controller and a dump load. If this system is well designed, almost no power is used by the voltage controller if the wind turbine is producing no power. The dump load is only activated if the charging voltage is higher than the maximum charging voltage of the battery. It might be that the voltage at which the dump load is activated is adjusted too low for the nominal battery voltage or that the system contains an analogue volt meter which is always dissipating some power.

A free manual of a 27.6 V, 200 W battery charge controller is given at my website: www.kdwindturbines.nl at the bottom of the menu KD-reports. The wire diagram of the voltage controller is given in figure 1 of the manual. The battery voltage is available over the resistors R1, P1 and R2 which are connected in series. The total resistance is 26700 Ohm. So the current at a battery voltage of 24 V is 24 / 26700 = 0.0009 A. So the power loss is
24 * 0.0009 = 0.0216 W. It will take a very long time to empty a 24 V battery with this power.

The problem of heat generation in the generator at high rpm is especially large for battery charging. The battery charge controller makes that the voltage is kept at a constant value. The generator efficiency decreases strongly at increasing rotational speed if the voltage is kept constant (see measurements given in report KD 78). This makes that heat generated in the winding increases strongly at increasing rpm. So if the wind turbine has a low cut-in wind speed, the voltage at high rpm will be very much lower than the unloaded voltage. Wind turbines which are grid connected by an inverter are much better on this point because the inverter accepts a low voltage at low rpm and a high voltage at high rpm and this makes that the generator efficiency is also high at high rpm.

I bet the weather condition in Finland can be detrimental on small ( and bigger turbine ) as the freezing conditions might start already in September.