Tuesday, May 10, 2016

Wind Energy Not Intended to Be Constant

Subtitle:  Wind Energy Supplements Other Forms

There is a massive misconception among the wind-energy detractors, one that should be readily apparent but is not.  The problem is the wind-energy detractors say that wind-turbines can never replace baseload, steady power plants such as nuclear, coal, or even gas-fired power plants.    That misses the point, entirely.   This post addresses this and provides a bit of history of wind power. 

Motor-sailer Yacht
Photo By David J. Shuler - Nordhavn Corporate Headquarters, CC BY 3.0,
The first point is that wind is not steady, at least not in most places where wind-turbines would and are being built.  This is nothing new and should be obvious.  From the earliest days of sailing, those in the boats knew that sometimes the wind blew nicely and sailing was easy, sometimes the wind stopped and either the ship stopped or sailors had to row, and sometimes the wind blew fiercely and at times capsized the ship.   On land, similar things occur with the wind, totally calm, a nice breeze, or a devastatingly strong force. 

Therefore, at least up until quite recently, electricity generated by wind-turbines has been a supplemental source of power, not a replacement for the baseload forms of generation.  More later on the innovations that have changed that.    Wind-turbines act to supplement the traditional forms of power generation. 

An analogy is to consider a a bicycle ridden at constant speed up a slight slope, as a load-following power plant of a gas-turbine design.  The power that the rider must input to the pedals corresponds to the fuel the power plant consumes.   However, when the bicycle reaches a point on the road where the slope is not quite as steep, less pedal-power is required to maintain speed.   The more gentle slope is analogous to the wind-turbines in operation, they make the gas-turbine power plant use less fuel.    A more exact analogy would be a bicycle being ridden on a road with a slope that changes from time to time.  The changes in slope correspond to changes in the wind speed.  A flatter or more gentle slope corresponds to stronger wind.  A steeper slope corresponds to a decrease in wind speed.  

The same analogy holds for solar energy, where strong sunshine produces less slope for the bicycle.  Clouds passing over the solar energy plant cause the gas-turbine plant to use more fuel as the solar plant's output falls.  This corresponds to a slightly greater slope the bicycle must ascend.  

Another analogy is a ship that has both an engine and sails.  The sails plus engine can be used to achieve a constant speed.  When the wind blows stronger, the engine throttle can be reduced, and vice-versa.  see photo above. 

Therefore, it can be seen that wind-turbines alone can not replace load-following or baseload power plants.  They can, however, reduce the fuel consumed.   Next, the options available to a utility grid-operator when wind-turbines or solar, or both, are supplying power to the grid. 

When the amount of wind-energy is small, under 5 percent, the grid operator typically does little more than he did before the wind-turbines existed.  The load-following capability of power plants designed to follow the load cope quite well.  However, when wind-energy reaches a substantial fraction of the grid's load, perhaps 30 percent or a bit higher, the grid operator must take steps to ensure grid stability when the wind suddenly stops, or the speed increases from almost zero to 25 or 30 miles per hour.   These issues are discussed at length in the electrical engineering professional journals.  

The key issue is response time, the time required for other generators to either reduce their output when the wind blows more strongly, or increase output when the wind dies.   This is where fast-response storage systems are valuable.  Technologies such as high-speed flywheels, batteries, and hydroelectric are fast-responding.  However, the first two are very expensive, or have been up to now.   A fourth technology was recently patented and obtained environmental permits to proceed, this technology is the ARES rail energy storage system.  see link.   

Also, improved batteries with lower cost are in development by BioSolar Inc, with prototypes for industrial testing due to be in service in second half of 2016.  see link 

Another option available to the grid operator is to de-energize some of the wind-turbines during high wind episodes, or gusts that give highly variable output.   However, where grid-scale storage is available, such as the above four technologies, the grid can be balanced by appropriately charging the storage systems.   Of course, the storage systems have a limit and once they are fully charged, some of the wind-turbines must be idled. 

Roger E. Sowell, Esq.
Marina del Rey, California

copyrignt © 2016 by Roger Sowell, all rights reserved

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