Control is a key enabling technology for the deploy-ment of renewable energy systems. Solar and wind power require advanced control techniques for high-performance and reliable operation. Eduardo F. Camacho, Tariq Samad, Mario Garcia-Sanz, and Ian Hiskens Introduction The use of renewable energy increased greatly just after the first big oil crisis in the late seventies. At that time, economic issues were the most important factors, hence interest in such processes decreased when oil prices fell. The current resurgence of interest in the use of renewable energy is driven by the need to reduce the high environmental impact of fossil-based energy systems. Harvesting energy on a large scale is undoubtedly one of the main challenges of our time. Future energy sustainability depends heavily on how the renewable energy problem is addressed in the next few decades. Although in most power-generating systems, the main source of energy (the fuel) can be manipulated, this is not true for solar and wind energies. The main problems with these energy sources are cost and availability: wind and solar power are not always available where and when needed. Unlike conventional sources of electric power, these renewable sources are not “dispatchable”—the power output cannot be controlled. Daily and seasonal effects and limited predictability result in intermittent generation. Smart grids promise to facilitate the integration of renewable energy and will provide other benefits as well. Industry must overcome a number of technical issues to deliver renewable energy in significant quantities. Control is one of the key enabling technologies for the deployment of renewable energy systems. Solar and wind power require effective use of advanced control techniques. In addition, smart grids cannot be achieved without extensive use of control technologies at all levels. This section of the report will concentrate on two forms of renewable energy—wind and solar—and on the role of smart grids in addressing the problems associated with the efficient and reliable delivery and use of electricity and with the integration of renewable sources. Solar and wind power plants exhibit changing dynamics, nonlinearities, and uncertainties—challenges that require advanced control strategies to solve effectively. The use of more efficient control strategies would not only increase the performance of these systems, but would increase the number of operational hours of solar and wind plants and thus reduce the cost per kilowatt-hour (KWh) produced. Both wind and solar have tremendous potential for fulfilling the world’s energy needs. In the case of wind, if conventional onshore wind turbines with 80-m towers were installed on 13% of the earth’s surface, the estimated wind power that could be commercially viable is 72 terawatt (TW). That amounts to almost five times the global power consumption in all forms, which currently averages about 15 TW. With capacity that has tripled in the last five years, wind energy is the fastest growing energy source in the world. Using larger wind turbines to convert kinetic energy into electricity has significantly increased the average power output of a wind turbine unit; most major manufacturers have developed large turbines that produce 1.5 to 3.5 megawatts (MW) of electric power, even reaching 5 to 6 MW per Control for Renewable Energy and Smart Grids From: The Impact of Control Technology, T. Samad and A.M. Annaswamy (eds.), 2011. Available at www.ieeecss.org. turbine in some cases. At the end of 2009, with 159.2 gigawatt (GW) of wind-powered generators worldwide, primarily grouped together to create small wind farms, the global collective capacity was 340 terawatt-hour (TWh) of energy annually, or 2% of global electric energy consumption. Several countries have achieved relatively high levels of wind power penetration: about 19% in Denmark, 14% in Spain and Portugal, and 7% in Germany and Ireland. Government subsidies have been a key factor in increasing wind power generation. These subsidies, in turn, have often been justified by the renewable portfolio standards (RPSs) that several countries have adopted and that require increasing the production of energy from renewable sources. In particular, RPSs generally obligate utilities to produce a specified fraction of their electricity from renewable energy. The European Union has a regionwide RPS of 20% by 2020; the United States of 20% by 2030, with different targets and years depending on the state (for example, 15% by 2025 in Arizona and 20% by 2020 in Colorado). Although wind energy is a clean and renewable source of electric power, many challenges must be addressed. Wind turbines are complex machines, with large flexible structures working under turbulent and unpredictable environmental conditions, and are connected to a constantly varying electrical grid with changing voltages, frequency, power flow, and the like. Wind turbines have to adapt to those vari。