Texas turns to Gas-Fired Power Plants to meet Peak Electric Demand their Wind Power cannot Meet

Posted by PITHOCRATES - June 30th, 2012

Week in Review

Texas has more wind-generated electricity than any other state in the country.  According to the American Wind Energy Association’s U.S. Wind Industry Fourth Quarter 2011 Market Report Texas has a total installed nameplate capacity of 10,377 Mega Watts (MW).  Meaning these wind turbines can produce 10, 377 MW under ideal wind conditions.  But as wind conditions are rarely ideal these Texas wind farms will struggle to produce half of that nameplate capacity.

Wind power has a capacity factor of about 20-40%.  Wind turbines will only produce electricity for a range of winds.  They have to spin fast enough to produce electric power at 60 cycles per second so they can connect this power to the electric grid.  But not so fast that they could damage the turbines.  For that range of winds variable pitch blades on the ‘propeller’ adjust their angle of attack to produce 60 cycles per second in that wind range.  The ‘propellers’ won’t spin that fast.  But a gear box will gear up that constant rotational motion to spin an electric generator (or alternator) at 60 cycles per second.  Thus creating electric power that we can connect to the grid.

So, of that 10,377 Mega Watts Texas nameplate capacity it will provide at most 4,151 MW (40% capacity factor) of power to add to the electric grid.  Which explains why the state with the greatest amount of wind-generated electric power is turning to coal and natural gas to meet peak electric loads (see Texas prepares for soaring power demand, urges conservation by Eileen O’Grady and Scott DiSavino posted 6/25/2012 on Reuters).

Power demand reached 65,047 megawatts in the hour between 4 p.m. and 5 p.m. CDT (2200 GMT), surpassing the June record of 63,102 MW set last year, according to preliminary grid data…

ERCOT [Electric Reliability Council of Texas] said demand may top 66,000 MW on Tuesday. The state’s all-time peak use of 68,379 MW was set in August of last summer during a protracted heat wave and drought…

ERCOT warned that rolling outages could occur this summer given the state’s limited amount of surplus generation…

Several idled power plants have been returned to service to bolster the summer supply after a new coal-fired plant expected to be operational was delayed.

NRG Energy (NRG.N), the state’s second-largest power company, has more generation available this summer than last, after restarting a half dozen older, natural gas-fired units totaling 1,100 MW that were previously in mothball status.

The one thing conspicuous by its absence in the entire Reuter’s article is the mention of all that wind power in Texas.

Texas is the number one wind-power state.  Still, the useable power from all those windmills (about 4,000 turbines in total) is only 6.38% of that peak demand.  Some 4,000 wind turbines to produce about 4,151 MW.  The same amount of electric power some 23 older, moth-balled, gas-fired power plants can produce.  Which is probably why they’re talking about rolling outages.  Because they’ve been building wind farms instead of useful power generation plants.  Fueled by natural gas.  And coal. 

Incidentally the capacity factor for a coal-fired plant is about 90%.  Where the only thing limiting its output is maintenance or low demand.  A nuclear power plant can have a capacity factor exceeding 100%.  For these reasons coal and nuclear power provide a large percentage of reliable power.  During peak demands natural gas-fired ‘peaker plants’ come on line quickly to provide for the extra demand when people come home from work and turn up their air conditioners.  While wind and sun add into the mix as more a novelty than a reliable power source.  With the capacity factor of solar power coming in on average around 12-15%.  In the south they may attain as high a capacity factor as 20%.  Like wind.  Making both of these a poor choice to provide additional power during peak demand.  Which is why Texas is firing up gas-fired ‘peaker plants’ to meet that peak demand.  Because they can.  While they have no way to make the wind blow or the sun shine on demand.

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