Residential Wind by Way of Illustration - Wind Power for the World: The Rise of Modern Wind Energy - page 583

panel or wind turbine. Most of the time the customer craves for
energy, and wind controller does its best by peak power tracking.
But there are inevitably intervals of time when the wind is
plentiful while need for energy is low and the battery is already
fully charged. In such a case Turbine controller initially engages
a dump load. It does that gradually while maintaining optimal
battery voltage (most other controllers just apply full available
dump load at once, give it some time and disconnect it). If dump
load is not sufficient or totally absent, the controller turns to
something opposite to peak power tracking—it makes the blades
operate at such speed that the amount of power taken from the
given wind is small. For that it has yet another curve in its memory,
again voltage as a function of current, which provides a low flow
of power to the battery to keep it fully charged, but prevent over-
charge and damage. An additional benefit is that the blades
become slow and produce low audible noise. Company pioneered
this mode in Turbine controller. It has become a common feature
of turbine controllers throughout the industry since then.

26.7 Stop Mode

If you go to a driving school, the first thing they teach you is
braking. That seems counterintuitive; the name “driving” implies
diferent skills. Though the purpose of wind turbine is producing
power, it is frequently important to stop it. Slow mode not always
reaches its objective of preventing battery overcharge. In that
case, the controller stops the turbine. There is need to do that for
safety reasons or to prevent mechanical damage from very strong
winds as well. Savvy turbine owners sometimes install a shorting
switch to stop the turbine. But the controller “knows” better
than simple shorting, it is equipped to do that intelligently. The
turbine is stopped when the energy accumulated in its rotating
parts is taken away. The more power is taken, the faster the turbine
stopped. Sounds very similar to peak power tracking, doesn't
it? There is one significant diference: the goal is to take as much
energy as possible, not to produce maximal sustainable output of
electrical power for the given wind. Unlike peak power tracking,
losses are also useful in decelerating the turbine. If the turbine
is just shorted, the only real place where energy is dissipated is