Recent results on the integration of variable renewable electric power into the US grid
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REVIEW Recent results on the integration of variable renewable electric power into the US grid
Jay Apt, Tepper School of Business and Department of Engineering & Public Policy, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA Address all correspondence to Jay Apt at [email protected] (Received 11 September 2014; accepted 11 May 2015)
ABSTRACT New research results in several areas that can help to facilitate the large-scale integration of variable renewable power sources into the electric power system are reviewed. Increasing the market share of variable renewable electric power generation in the United States from the present 4% is eminently feasible, and can be facilitated by recent research. The amplitude of variability of wind and solar power is much less at high frequencies than at low frequencies, so that slow-ramping generators such as combined-cycle natural gas and coal can compensate for most of the variability. The interannual variability of wind power is beginning to be understood, as are the biases in its day-ahead forecasts. Geographic aggregation of wind and solar power has been proposed as a method to smooth their variability; for wind power, it has been shown that there is little smoothing at timescales where the magnitude of variability is strongest. It has also been shown that the point of diminishing returns is reached after a relatively few wind plants have been interconnected. While good prospects for lower cost electric storage for grid applications exist, the profitability of storage for integration of renewable power is likely to remain a difficult issue. New extremely efficient, low pollution, and fast-ramping natural gas plants have come on the market. It is now possible to predict the amount of additional capacity of this sort that must be procured by system operators to cover the uncertainty in wind forecasts. Keywords: energy, renewables, electricity
DISCUSSION POINTS • The variability of wind and solar electric power is a consideration when integrating increasing amounts of renewable electric power. • Interconnecting many wind plants with large transmission lines is not a cost-effective method to smooth variability, but other methods are available. • While electric energy storage is helpful in smoothing out variability so that transmission lines can be more fully utilized, storage is unlikely to be profitable at large scale.
Introduction Air pollution from the generation of electric power degrades human health1,2 and is a major source of greenhouse gas.3 Low-pollution sources such as some renewable electric energy generators are one option for reducing such emissions. Renewable energy as a percentage of electricity generation in the United States fell from 30% in 1950, when hydroelectric
power was the only significant renewable, to a low of 8% in 2001, as the market share of hydroelectric power was eroded by fossil fuel generation that was built to keep up with rapidly increasing demand for electricity* (Fig. 1). By 2013, renewables' market share had increased to 13%, primaril
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