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Integrating Renewables

Opportunity for advancement or exercise in futility?

Fortnightly Magazine - March 2010

competitive within the next three to five years.

• Non-Utility Generation: Possibly for the first time, major generation will be built by companies and people who don’t have a utility mindset. Many of them are property owners or developers. Utilities will need to understand regulatory requirements for accommodating non-utility renewables—such as net-metering arrangements and interconnection standards—and implement them where they’re needed instead of trying to apply them across the entire service territory, at an unnecessarily high cost. In addition, non-utility projects tend to get implemented much faster than conventional generation, which means interconnection processes need to speed up.

Key Mechanisms

There are several factors that need to be considered when identifying mechanisms for managing and operating renewable resources: The first factor is siting constraints and characteristics. The location of wind or solar farms is a significant factor regarding management and operation. Important aspects of siting include the ability to: appropriately locate generation facilities in areas of high-energy resource availability; provide transmission corridors to deliver energy from generation to load; and effectively forecast power generation levels and schedules.

Generation from solar, wind, geothermal, etc. , each have specific output characteristics. Even within solar, for example, the output characteristics of different types of solar cells operate differently under different conditions. When combined in large output modes ( i.e., as in a wind farm) behaviors will drive their impact to the grid under different conditions. This specific characteristic actually can be a benefit, in that it can smooth out the rapid fluctuations of wind-energy output to a certain extent. Mechanisms exist to model this information into the forecasting approach so that the variability in the source can be converted into variability in the delivery of power into the grid.

But a key sticking point in the integration of renewables is the availability and ability to build transmission lines and corridors to bring the power from renewable sources into the load centers. This problem has more of a policy aspect than a technical aspect to it. Policy mechanisms are being considered toward finding a solution.

Also, wind and solar energy forecasting has been the focus of much research at DOE laboratories and universities for several years now. The current focus is on forecast error and determining how these sources of generation will fit into the market models and support the balancing authority.

A key aspect of forecast error involves a concept called the “tail event.” A tail event happens when forecast errors for load and wind result in divergence of power demand and supply. Large wind power ramps in a power system (see Figure 1) can create significant imbalances between generation and load, resulting in grid instabilities. Such events occur infrequently but are much more substantial as the market penetration of wind increases.

A second major factor is the use of technology and automation. Two key areas of technology and automation under serious consideration for renewables integration include hardware and software systems.

Examples of hardware systems include synchro-phasor monitoring units (SPMUs), static VAR compensators (SVCs) and flexible AC transmission systems (FACTS). SVCs and FACTS devices