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A World Bank Study
generation can be integrated if grid operators, policy makers, and regulators are willing to take the necessary steps of undertaking mitigating actions, incorporating forecasting, and procuring additional reserves if necessary. Furthermore, variable generation integration studies are not substitutes for detailed transmission studies and plans, nor are they substitutes for the interconnection studies that are done to determine the reliability impacts of hooking a proposed generator to the grid. Those detailed transmission and interconnection studies evaluate specific individual transmission projects or generation plants, while a variable generation integration study examines potential scenarios of higher levels of wind and solar capacity from an aggregate, systemwide perspective. Variable generation integration studies are typically data and labor intensive and can take a year or more to compile. There are several components to a variable generation study: • Production cost modeling for hourly simulations of power flows, costs, and dispatch • Statistical analysis for determining hourly deviations in net load from adding wind and subhourly variations • Capacity value and reliability analysis for assessing the capacity value of wind and solar generation • Load-flow analysis for determining the transmission flows that occur with higher levels of variable generation, evaluating congested transmission flowgates, and determining the transmission additions that are needed. The transmission system is studied both unconstrained (under a “copper sheet” analysis) and constrained • Sensitivity studies, such as assessing the impacts of different fossil fuel prices, different fuel mixes, higher or lower projected electricity demand, different operating levels of coal plants (more flexible versus less flexible), different levels of hydro flexibility (again, more flexible versus less flexible), and varying accuracy of forecasts of variable generation. Figure C.1 illustrates how a typical variable generation study is structured and sequenced. Variable generation studies are data and time intensive, involve multiple organizations, and can typically take a year or more to do. Ideally, a single organization organizes and leads the study, with help from other organizations and a study technical review committee as needed. Although variable generation studies can be conducted in-house, they are often contracted out to multiple consultants with expertise in power systems, transmission load flows, and variable resource production and forecasting. Data to be included in a variable generation study are for at least one year and preferably multiple years. The study includes time-synchronized wind, solar, and load data to capture interannual variability of load and wind. Load