Optimizing The Wind Energy Resource

February 22, 2014 by  
Filed under Green Energy News

Much has been written concerning the difficulty of integrating wind power into the electric grid. Of significant note was last year’s New York Times article that highlighted the issue of curtailment – the practice of reducing the amount of wind energy produced because it cannot be integrated into the power grid.

However, while integration and curtailment can be real issues, they need not be that significant, if the proper planning occurs and if systems and transmission infrastructure are put in place. And real economic gains can occur as a consequence.

In discussing the issues of getting more wind power onto the system, it is important to distinguish between the issues of curtailment and intermittency. As noted above, curtailment is the practice of reducing the wind output. Wind gets curtailed because turbines in remote locations lack the transmission routes to market.  Intermittency is an unrelated issue having to do with the fact that the wind constantly changes and turbines produce varying amounts of electricity as a result. That problem can be addressed through better planning and forecasting approaches.

In the past few years, considerable progress has been made in both these areas. In fact, the American Wind Energy Association (AWEA) reports that as the number of wind turbines has ramped up, the amount of wind energy curtailed has fallen considerably, from 9.7% in 2009 to 4.9% in 2011, down to 2.7% in 2012 (2013 numbers for the nation are not yet available). Meanwhile, integration costs have also fallen in certain markets.

Texas Gets Wind Right

The example of Texas shows how this can be done on a broad scale, with significant economic benefits as a result. In fact, curtailments in Texas have declined from over 17% in 2009 to 3.8% in 2012 and only 1.2% In 2013.  The first thing Texas did was to look at the big picture. They recognized the economic value of wind, took a proactive and integrated approach to developing their wind resource, and committed to building the requisite transmission capabilities. In 2005, the Texas Legislature directed the Public Utilities Commission (PUC) to designate geographic areas for wind farms, called Competitive Renewable Energy Zones (CREZs).  In 2008, the PUC designated five CREZs, and laid out the transmission requirements necessary to deliver wind energy to the market.  This infrastructure has now been completed and the newly added 3,600 miles of transmission lines increase the state’s wind capacity to a total of almost 18,500 MW.

Between 2008 and the end of 2013, the Electric Reliability Council Of Texas (ERCOT) had signed interconnection agreements with almost 9,000 MW of new wind resources. Almost 7,000 MW of this capacity are expected to be installed between now and 2016. This represents nearly all of the additional capacity established by the CREZ lines.

However, the availability of transmission lines represents only part of the story. The other piece has to do with how ERCOT manages the transmission lines, as well as its improved approach to forecasting and integration of the wind resource.

In the past, conservative assumptions were used concerning line loads and risk of system collapse. Today, better computers allow ERCOT to recalculate the related information on an hourly basis.  In particular, ERCOT adopted a new tool (real time stability analysis), which explicitly manages the West to North interface on the Texas power grid. The process allows operators to monitor Real-Time conditions for generation and “continuously inform operations which limit is currently effective.”  While this tool does not explicitly focus on the wind resource, it improves the ability to move more wind energy out of West Texas while maintaining reliability of the grid. As such, it helps to further reduce the amount of wind energy curtailed.

Not surprisingly, this more granular forecasting approach allows for more precision – with the result that hundreds of additional megawatts of power can be moved out of West Texas. And this improves the overall economics considerably, by tens of millions of dollars.

Better forecasting further improves wind economics by reducing the integration costs of this intermittent resource. ERCOT’s forecasting occurs every five minutes, with regulation (generation facilities that can quickly start or stop) helping to smooth out the variability. On top of that, there is forecasting for uncertainty on a day-ahead basis. This uncertainty must be addressed by other generating resources call non-spin reserves (they have to be ready to start up with longer lead times in order to balance out bigger variations in wind output).  According to one analysis, the total annual costs for the 2011 period were on the order of $16.6 million, compared with the total value of the wind resource at $1.3 billion.  Put another way, those integration costs work out to as low as $.50 per megawatt-hour, far below the commonly assumed costs (which can sometimes be estimated as high as $5/MWh according to AWEA). A report cited by the DOE put this number at $1.2/MWh – still significant lower than earlier estimates.

Other Regions Follow Suit

With energy in the best wind regimes coming in at $20-30/MWh (two to three cents per kilowatt-hour), there is a growing incentive to get this right.   Other regions, such as the Midcontinent Independent System Operator (MISO) which covers 15 states in the middle of the U.S., as well as Manitoba), are adopting an approach similar to that of Texas.

MISO began its investigation in 2002, and after much study, established a policy of cost allocation to support construction of transmission lines that would link up to 15,000 MW of new wind supplying up to 41 million MWh annually into the system.  This transmission capability would also help member states meet their internally established renewable portfolio standards. Like Texas, MISO created a wind development portfolio “based upon a set of energy zones, developed to provide a low-cost approach to wind siting when both generation and transmission capital costs are considered.”

MISO also utilizes a similar fast resource dispatch system so they can stay on top of variability associated with the intermittent wind resource. The approach has been successful to date, with MISO noting in a 2012 presentation that, “the Impact of intermittent generation in general is little to none.” MISO further notes that ‘the impact of short term wind forecast error in net load uncertainty is low.” The impact of intermittent generation is “none” and only a potential issue where a single wind farm were to exceed 2,000 MW.

The Southwest Power Pool (SPP) is also getting into the act, with a similar policy to allocate the costs of new transmission. The SPP is also switching to a nodal 5-minute market (similar to ERCOT), which will facilitate improved integration of the wind resource.

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