24 May 2011: The International Energy Agency (IEA) has published a book titled “Harnessing Variable Renewables: A Guide to the Balancing Challenge,” which presents a method of assessing resources needed to balance supply and demand in power systems utilizing large shares of variable renewable energy (VRE), such as solar photovoltaic, wind and tidal energy.

The book contains sections on, among others: why variability is a challenge; why flexibility is the right response; key distinguishing features of power systems; the Flexibility Assessment Method; identifying the flexible source; how much of the flexible resource is available and how much is needed; the costs of balancing VRE; and case studies of eight geographic regions with different power attributes that show greater technical potential for balancing variable renewable energy output than is commonly assumed.

The Flexibility Assessment Method to identify VRE potential to balance increasingly variable supply and demand presented in the book includes four steps: step one assesses the maximum technical ability of flexible resources to ramp up and down over the balancing time frame; step two captures the extent to which certain attributes of the power area in question will constrain the availability of the technical resource; step three calculates the maximum flexibility requirement of the system, which is a combination of fluctuations in demand and VRE output, and contingencies; and step four brings together the requirement for flexibility and the available flexible resource to establish the Present VRE Penetration Potential (PVP) of the system.

Among the main conclusions of the book are that balancing variable renewables is possible, although planning is required, and that avoiding price pressure on conventional plants during peak times of variable renewable electricity production remains a major challenge. [Executive Summary] [IEA Press Release] [Publication: Harnessing Variable Renewables: A Guide to the Balancing Challenge]