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The conventional wisdom is that hydraulic
or fossil fired plants can be operated at less than full power to
accommodate the wind generation.
From my reading, stable operation for a fired
thermal generator is normally from about 50% of the unit rating up to
full power. For reduced power operation some units add oil to supplement
the coal feed and maintain stable "firing" conditions. Thermal units range
in size, but are typically a few hundred MW.
EON Netz report that wind generation in excess of
20% of the grid demand can lead to instability conditions due to
variability. Another real condition arises on those occasions
when the total output of the installed wind generation is very
small. EON Netz, with 7000 MW of wind generation, rely on only
8% in their supply in planning. This means they can count on only 560
MW from the wind turbines, and must have sufficient "spinning reserve"
to accept rapid loss of wind generation capacity. Hence, there must
be a number of thermal units running at 50% of capacity (or more)
to be available to respond.
Alas, heat engines running at 50% are usually less
efficient than those running closer to their unit rating. (This is one
aspect where diesel engines perform well.)
From the point of view of meeting the power demand,
including the installed nameplate capacity of wind generators is
misleading. The Ontario supply plan had better include sufficient
energy import capacity to provide a real margin on the load demand rather
than a mythical one.
Another aspect of electrical generation that isn't
often mentioned is "VAR generation". The whole issue of managing reactive
power loading on the distribution system is handled better in Europe than in
North America. European standards require the owner of the load to control
their power factor (phase angle between voltage and current) and harmonic
characteristics. In North America these characteristics of loads
are less well regulated, leaving the utilities and the customers
in a confused state about whose equipment did what, and who pays to
condition the power.
Anyway, most wind generators aren't capable of
generating "reactive power". (It would be a cheap shot to say that they
are good at generating imaginary power, so I won't.) Some are being
equipped with solid state equipment to improve on this aspect.
The wind is free. Wind generated electricity
isn't. Not by a long shot.
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