In general, you dump load power consumption should be larger than you maximum generation power. It must of course also be less than what your controller's maximum current is as well. I would probably look for a dump load which would draw about 15 or 16 amps for your setup, in other words about 250 Watts at a typical dumping voltage in sustained high winds. My experience with dumping is more with solar, but the principles are the same.
from Ohm's law:
Resistance = square of voltage / power
If you wanted your dump to consume about 250 Watts at 15 volts then you would aim for about .9 Ohms total resistance.
If you are using resistors, then you can connect several resistors in parallel to achieve the desired total resistance.
Total Resistance = 1 / ((1/(1st resistance) + 1/(2nd resistance) + 1/(3rd resistance))
where the (1st resistance) represents the value in Ohms of the resistance of the 1st resistor. The example is for three resistors parallel, but it can be calculated for any number of parallel resistors in a similar manner.
For example four resistors each of a value of 4 Ohms in parallel would have a total resistance of one Ohm, which would be in the ball park of what you need.
Keep in mind that each of those resistors would have to be capable of dissipating (rated at or above) a sizable amount of power. If the maximum possible voltage was to be 16V or less this would be:
P = square of voltage / resistance = 16 squared / 4 Ohms = 64 Watts
That would give you a total power dissipation of 256 Watts at 16 Volts, and the current at this voltage, which would also be the maximum would be 16 Amps.
Hopefully I didn't make any basic math errors, and hopefully this helps a bit for calculations based upon whatever resistors you have available. Rich