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✔ The capacity of the Grayson Repowering Project is driven to reliably serve the needs of the residents and businesses of Glendale. Without the Grayson repowering and after Units 1-8 are no longer capable of running, the available capacity through imports from outside sources and the one newer unit at Grayson Power Plant—Unit 9—is 287 MW. 

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GWP must have in place sufficient reserve sources of power to cover both the “loss of the single largest contingency,” which is referred to as its “N minus 1” or “N-1” “contingency” and its second largest contingency, which is referred to as its “N minus 1, minus 1” or “N-1-1” “contingency” and involves two contingencies – the loss of Glendale’s two largest resources -- happening consecutively. This means that we must maintain enough generating capacity to power the City even if there is an unexpected failure or loss of our largest two sources of power. For GWP, the largest single source of power is the DC Intertie line, which transmits 100 MW of power to the City. See image of GWP’s sources of power here. In fact, partial and complete loss of the DC Intertie line has occurred in the past, and some of the outages have been for extended periods of time. In addition, reserves must also be in place to re-establish reserves within one hour. With the loss of GWP’s single largest contingency, the City would have only 187 MW of supply available for meeting its obligations.  

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GWP’s next single largest contingency (N-1-1), after loss of the DC Intertie line, is assumed for planning purposes to be 71 MW, the loss of a unit at the power plant. If an N-1 event (the 100 MW loss of the Pacific DC Intertie) occurs, Glendale must plan and prepare for the loss of a 71 MW unit at the power plant (i.e., GWP’s N-1-1 contingency). This requires GWP to have 71 MW of replacement energy available within 10 minutes of the loss of the 71 MW generator. In this scenario, GWP has lost 100 MW of import capability on the Pacific DC Intertie and has subsequently lost 71 MW of local generation (before the 100 MW on the Pacific DC Intertie was restored).  Therefore, Glendale must replace 171 MW of “lost” energy supply on a potentially on-going basis (i.e., longer than one hour).  With the loss of GWP’s two largest single contingencies, the City would have only 116 MW of supply available for meeting its obligations.  

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GWP’s system load exceeds 187 MW more than 80 days a year and exceeds 116 MW daily. With respect to a peak day, GWP’s peak load is 350 MW (with no allowance for reserve margin) and there would be a shortfall of 163 MW associated with GWP’s N-1 contingency and a 234 MW shortfall if GWP had N-1 and N-1-1 contingencies.  Such shortfalls would have to be supplied by resources internal to the City. 

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The Grayson Power Plant, once repowered, would add a capacity of 262 MW at average annual conditions (64° F). On a hot day (95° F), that capacity would fall to 242 MW. On the peak load day (100°+ F), the available additional capacity would be slightly less.

With 242 MW available at Grayson Power Plant, the City would be able to cover both its N-1 and N-1-1 contingencies.  Thus, the Grayson Repower allows GWP to reliably serve Glendale by providing sufficient capacity to cover the loss of GWP’s two single largest contingencies and still meet load, as well as the non-operating reserve that could be started to provide the required spinning reserve.

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Additionally, as GWP imports increasing amounts of wind, solar and other variable sources of renewable energy into the City, and as more solar power is generated locally in Glendale, this creates increased fluctuations on the power grid. A steady, constant source of energy such as that from the Grayson Power Plant is needed to balance out (“firm and shape”) the energy so that that a smooth and steady supply of power can be delivered to GWP customers. The old units at the Grayson Power Plant do not have the ability to rapidly adjust up and down to account for variances in solar output, based upon weather patterns on a minute-per-minute basis. Modernizing Grayson will allow us to manage renewable energy flows dynamically, so that energy deliveries will continue to be reliable.