TODAY’S STUDY: GETTING MORE WIND AND SOLAR ON THE WEST’S GRID

An Analysis of the Impact of Balancing Area Cooperation on the Operation of WECC and the Compounding Effect of Wind and Solar Generation

Gary Jordan and Dick Piwko, February 2013 (National Renewable Energy Laboratory)

Introduction

One of the issues that arose in the Western Wind and Solar Integration Study, WWSIS, was the impact of Balancing Area (BA)size and the amount of coordination and cooperation necessary. Most of the production simulation cases in WWSIS assumed that the thermal and hydro generation in WECC would coordinate within the limits of the transmission system to best address variability and uncertainty imposed by wind and solar generation. This analysis uses a similar production simulation database, but with varyingBA sizes and hurdle rates to examine this question in greater detail. WWSIS used Western Electricity Coordinating Council (WECC) database developed from Ventyx data in 2008. The system was broken into 104 separate load and generation areas and used a simple “bubble model” to represent transmission constraints. This new database uses the November 2010 Ventyx version of a key source and uses a full transmission system representation. In both cases, the year 2017 was chosen for simulation. The average price assumed for natural gas was $7.50/Mbtu and carbon costs were ignored. The new version of the database models WECC with 41 load and generation areas that are largely aligned with the existing BAsin the WECC system.

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These areas were grouped into 28 companies and five large regions. These are defined in Table 1 and shown in Figure 1. Note that all the “areas” within the California Independent System Operator (CAISO) footprint were grouped into one “company” called CAISO.

It is not the intent of this analysis to exactly model the operation of the BAs within WECC. Rather, it is to examine the operational benefits of increased cooperation between a large number of operating regions. To that end, some approximations were taken with the data. Although they operate mostly independently, the separate companies do have remotely owned and jointly owned generation. Where that information was available, it was included in the analysis. In addition, each company was required to maintain a spinning reserve equal to 3% of the hourly load in this simulation…

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Results The total operating costs for the various cases are shown in Figure 2. The general trends are as expected. Increasing the boundaries between the companies, in either just the commitment or for both the commitment and dispatch, increases the total operating costs. The spinning reserve was held at 3% of load in all cases. In practice, the company-level spinning reserve may need to be higher than assumed here because 3% of the load may not be sufficient to cover generator contingencies in all hours. Increasing the penetration of renewable generation reduces the total operating costs, but shows the same general trends.

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Figure 3 shows the reduction from the high hurdle rate case for commitment and dispatch. This figure highlights the fact that increasing the coordination between the companies in both the commitment and dispatch will significantly increase the overall savings. (Note: Reducing the commitment and dispatch hurdle rate below the $5/MWh level did not have any significant impact on the operating costs. That indicates that it is the trade off of gas and coal energy that is providing the savings and not just the incremental value of slightly better heat rates.) Reducing the hurdle rate in the dispatch only and keeping the same level of commitment provides 20% to 40% of the total savings potential.

Another aspect of operation with renewables is the amount of spilled energy (i.e., wind or solar or hydro energy that could not be used). Figure 4 shows that low levels of cooperation in the company level dispatch results in higher levels of spilled energy. This shows that increasing the level of cooperation in the real time dispatch, even without modifying the commitment, will significantly reduce the amount of spilled energy. This result is even more important as the penetration levels increase.

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Figure 5 shows the impact on the level of generation by type for the company-level dispatch. For both levels of renewable penetration, increasing the hurdle rates for either just the commitment or for both the commitment and dispatch will reduce the operation of the base and intermediate generators (coal and combined cycle), and increases the generation from peaking units (gas turbines and gas steam units). Increasing the dispatch hurdle rate encourages companies to operate higher cost resources rather than taking advantage of cheaper resources available on neighboring systems. Having a high hurdle rate in the commitment makes a company less likely to turn on a low cost resource to sell to their neighbor.

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Conclusion

Increasing the cooperation between the many BAs within WECC can significantly reduce operating costs. Increased BA cooperation becomes more beneficial as levels of renewable generation increase. Maintaining existing commitment strategies, but increasing coordination in the real-time dispatch will significantly reduce the amount of spilled energy, but will only capture 20% to 40% of the total operating cost savings potential. The maximum savings result when both commitment and dispatch of generation is coordinated across the system.

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