Harjeet Johal

Integrating high levels of wind in Island systems: Lessons from Hawaii

Variability of power generation from intermittent resources such as wind and solar plants presents an operational challenge for grid operators. The economic incentives and technical challenges that accompany large amounts of variable generation in island power systems are often much greater. The Hawaiian Electric Company and its subsidiaries, the Maui Electric Company and the Hawaii Electric Light Company have considerable experience in planning and operating power systems with relatively high levels of wind power. The islands of Hawaii and Maui operate power systems with high levels of wind power (more than 10% by energy) and have experienced and addressed challenges associated with the variability and uncertainty of wind power. The island of Maui is anticipating further wind plant deployments in the near future. Recent analyses of possible near-term deployment of large amounts of wind power on the Oahu power system (500MW of wind power; approximately 1200MW peak and 520MW minimum annual load) has shown the potential for this system to accept almost 25% of its energy from wind and solar power. This paper will identify some of the wind integration challenges and highlight the benefits of a variety of strategies that are expected to improve system economics and operational reliability, including proposed modifications to the baseload thermal fleet (deeper turndown, higher ramp rates, and tuned droop characteristics), advanced wind turbine grid support features, new operating strategies, wind forecasting and refinements to the up and down reserve requirements. This paper will present the key findings in the context of useful insights and lessons learned that are relevant to other island power systems considering very high levels of wind power.

Demand response as a strategy to support grid operation in different time scales

Demand Response has been conventionally used as a resource to support the grid under steady state operating conditions by peak shifting or leveling the electrical load. The characteristics of responsive demand resources can also be used to support the grid during emergency and contingency conditions. Demand resources can respond very fast to provide ancillary services such as frequency regulation and operating reserves for the bulk grid; while the distributed nature of the resource can help in better solving local feeder level problems such as phase balancing, cold load pick up, etc. This paper presents some of these applications of demand response to support the grid under different time scales of operation; ranging from seconds to hours. The analysis will compare before and after benefits from using demand response, a controls strategy for using demand response, and its interface with the legacy grid controls for the above mentioned demand response applications.

An integrated approach for controlling and optimizing the operation of a power distribution system

Electric distribution grid is operated under a number of constraints in order to deliver power at a certain quality and reliability level. Electrical devices, such as capacitor banks, voltage regulators, and load tap changers are employed by the utilities to facilitate and support the operation of the distribution grid, while respecting many constraints, such as maintaining an acceptable band of voltage magnitude and a certain level of power factor. Traditionally, these devices are operated under fixed schedules, based on time of day or some other local parameters, and their operations are disjointed from one another, resulting in a decreased overall effectiveness of operation. This paper presents an approach to realize an integrated control and operation of these devices that will enable a more optimal operation of the grid. Simulation studies are performed on the IEEE test feeder network and the results highlight increased efficiency of grid operation in terms of decreased line losses, increased power factor, and improved voltage profile.

Grid integration of energy storage

Electricity as a commodity is markedly different from other commodities in the sense that it must, in general, be consumed when it is produced. The capability to store energy for a later use can help to improve the flexibility of power system operation by providing control of power as and when required. With a strong push towards increasing the reliance on renewable energy resources, a flexible power system is desired; one that can accommodate increased variability and uncertainty of generating resources. Energy storage is one strategy for enhancing the flexibility of power system operation. The application for energy storage can be broadly classified into energy applications (bulk transfer of energy from one time to another) and power applications (fast injection/absorption of power). There is also a broad spectrum between energy and power applications. The selection of a storage system as a means of adding flexibility to the grid depends upon a number of factors: cost being an important one. Other strategies that can offer flexibility in todays power system include demand response and fast-start generation with high ramping potential.