Thursday, 10 May 2012

The LE-600 48v wind turbine is designed to charge a nominal 48v battery bank

The LE-600 48v wind turbine is designed to charged a nominal 48v battery bank. The way this works is that once the turbine begins to turn, voltage is generated as the turbine speed increases. At this stage, the turbine is off-load and has not yet 'cut-in'. When the LE-600 reaches approximately 290rpm at 3m/s (its designed cut-in speed) the turbine voltage will have increased to level of the battery voltage, in this case 48v nominal. This cut-in speed is by design as the turbine blades need to be rotating fast enough to generate lift before any load is drawn from them. As the turbine speed and voltage continues to increase with windspeed, the batteries 'hold' the turbine voltage down and the turbine instead delivers current to the batteries.

Charging batteries is very simple for the wind turbine. The batteries are effectively a resistance and current is delivered from the turbine and into the batteries following the principles of ohms law.

Using any grid-tie inverter is far more complicated as the simplicity of ohms law is not present.
Instead, the inverter has to be programmed with a MPPT curve which tells the inverter how much power to draw from the turbine judging by the turbines speed. Draw too much power to soon, and the turbine will stall. Draw too little power and the turbine will run very fast and noisily and will not generate much power. The inverter monitors the turbines output voltage and uses that as an analogy for speed. To further complicate the situation, once the turbine is 'on-load' and doing work, its output voltage is no longer proportional to the speed. Thus the MPPT curve that is programmed into the inverter is quite important!

The Windmaster 500 has a voltage range of 25-125 volts in which the MPPT can be programmed. When using a Windmaster 500 with the LE-600, the MPPT curve is programmed between 25-65v.
We have found in our testing, that a LE-600 neither a 48v or 24v are quite right for use with the Windmaster and thus we developed the GT1 variant. In a way you could describe the GT1 variant as a '30v' variant. It puts the voltage characteristics of the turbine in-line with the aerodynamic characteristics of the turbine blades and the electrical characteristics of the Windmaster 500 and the MPPT curve that is programmed into it.

Turbines of different manufacture have different aerodynamic / electrical characteristics and some use 48v turbines with the Windmaster 500. There are a lot of variables and this might be ok with other turbines, but we weren’t quite happy with that and so developed the GT1 variant.

It would be possible to use a 24v or 48v LE-600 with the Windmaster, but the performance would be sub-optimal  and in any case we have developed the GT1 variant especially for the Windmaster 500.

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